Formerly known as Earth Viewer, Google Earth was developed by Keyhole, Inc., a company acquired by Google in 2004. The product was renamed Google Earth in 2005 and is currently available for use on personal computers running Microsoft Windows 2000, XP, or Vista; Mac OS X 10.3.9 and above; Linux (released on June 12, 2006); and FreeBSD. In addition to releasing an updated Keyhole based client, Google also added the imagery from the Earth database to their web based mapping software. The release of Google Earth caused a more than tenfold increase in media coverage on virtual globes between 2005 and 2006,[3] driving public interest in geospatial technologies and applications.
Denver, Colorado, viewed in Google Earth, now almost completely modeled with high-quality 3D models.
The viewer will show houses, the color of cars, and even the shadows of people and street signs. The degree of resolution available is based somewhat on the points of interest, but most land (except for some islands) is covered in at least 15 meters of resolution[4]. Las Vegas, Nevada and Cambridge, Massachusetts include examples of the highest resolution, at 15 cm (6 inches). Google Earth allows users to search for addresses (for some countries only), enter coordinates, or simply use the mouse to browse to a location.
Google Earth also has digital elevation model (DEM) data collected by NASA's Shuttle Radar Topography Mission. This means one can view the Grand Canyon or Mount Everest in three dimensions, instead of 2D like other map programs/sites. Since 23 November 2006, the 3D views of many mountains, including Mount Everest, have been improved by the use of supplementary DEM data to fill the gaps in SRTM coverage[5]. In addition, Google has provided a layer allowing one to see 3D buildings for many major cities in the US and Japan.
Many people using the applications are adding their own data and making them available through various sources, such as the BBS or blogs mentioned in the link section below. Google Earth is able to show all kinds of images overlaid on the surface of the earth and is also Web Map Service client.
Google Earth supports managing three-dimensional geospatial data through Keyhole Markup Language (KML). It is available in a free version, and in licensed versions for commercial use.
Downtown Los Angeles, using the 3D Warehouse feature.
Google Earth has the capability to show 3D buildings and structures (such as bridges), which consist of users' submissions using SketchUp, a 3D modeling program. In prior versions of Google Earth (before Version 4), 3D buildings were limited to a few cities, and had poorer rendering with no textures.
Many buildings and structures from around the world now have detailed 3D structures; including (but not limited to) those in the countries, the United States, Canada, India, Japan, United Kingdom,[6] Germany, Pakistan and the cities, Amsterdam and Alexandria[7]. Three-dimensional renderings are available for certain buildings and structures around the world via Google's 3D Warehouse[8] and other websites.
[edit] Sky mode
In version 4.2, released August 22, 2007, Google Earth added a Sky tool for viewing stars and astronomical images.[9] Google Sky is produced by Google through a partnership with the Space Telescope Science Institute in Baltimore, the science operations center for Hubble. Dr. Alberto Conti and his co-developer Dr. Carol Christian of the Space Telescope Science Institute, plan to add the public images from 2007,[10] as well as color images of all of the archived data from Hubble's Advanced Camera for Surveys. Newly released Hubble pictures will be added to the Google Sky program as soon as they are issued. Also visible on Sky mode are constellations, stars, galaxies and animations depicting the planets on their orbits.
[edit] Wikipedia and Panoramio integration
In December 2006 Google Earth added a new layer called "Geographic Web" that includes integration with Wikipedia and Panoramio. In Wikipedia, entries are scraped for coordinates via the Coord templates. If the options to show Wikipedia or Panoramio entries are selected, users will be presented with clickable dots in their current Google Earth view. When any of these dots are selected, the user will be shown the Wikipedia or Panoramio entry right in Google Earth. There is also a community-layer from the project Wikipedia-World. More coordinates are used, different types are in the display and different languages are supported than the built-in Wikipedia layer. See: *dynamic resp. static layer. Google announced on May 30th, 2007 that it is acquiring Panoramio.[11]
[edit] Influences
The Google Earth interface bears a noted similarity to the ‘Earth’ program described in Neal Stephenson’s sci-fi classic Snow Crash. Indeed, a Google Earth co-founder claimed that Google Earth was modeled after Snow Crash, while another co-founder said it was inspired by Powers of Ten.[12]
[edit] Specifications
Google Earth comes with atmosphere effects and seabed
Coordinate System and Projection
The internal coordinate system of Google Earth is geographic coordinates (latitude/longitude) on the World Geodetic System of 1984 (WGS84) datum.
Google Earth shows the earth as it looks from an elevated platform such as an airplane or orbiting satellite. The projection used to achieve this effect is called the General Perspective. This is similar to the Orthographic projection, except that the point of perspective is a finite (near earth) distance rather than an infinite (deep space) distance.[13]
Baseline resolutions
U.S.: 15 m (some states are completely in 1 m or better)
Germany, Switzerland, Netherlands, Denmark, England, Andorra, Luxembourg, Liechtenstein, San Marino, Vatican City: 1 m or better
Global: Generally 15 m (some areas, such as Antarctica, are in extremely low resolution), but this depends on the quality of the satellite/aerial photograph uploaded.
Typical high resolutions
U.S.: 1 m, 0.6 m, 0.3 m, 0.15 m (extremely rare; e.g. Cambridge and Google Campus, or Glendale)
Europe : 0.3 m, 0.15 m (e.g. Berlin, Zürich, Hamburg)
Altitude resolution:
Surface: varies by country
Seabed: Not applicable (a colorscale approximating sea floor depth is "printed" on the spherical surface).
Age: Images are usually less than 3 years old. The date next to the copyright information is often cited as the date the picture was taken, but this practice is incorrect.
Google Earth is unlikely to operate on older hardware configurations. The most recent downloads available document these minimum configurations:
Pentium 3, 500 MHz
128 MB RAM
400 MB free disk space
Network speed: 128 kb/s
16MB 3D-capable graphics card
Resolution of 1024x768, 16-bit High Color
Windows XP or Windows 2000 (not Windows ME compatible), Linux, Mac OS X
The most likely mode of failure is insufficient video RAM: the software is designed to warn the user if their graphics card is not able to support Earth (this often occurs due to insufficient Video RAM or buggy graphics card drivers). The next most likely mode of failure is Internet access speed. Except for the very patient, broadband Internet (Cable, DSL, T1, etc.) is required.
[edit] Mac version
Google Earth (Mac OS X)
A version for Mac OS X was released on January 10, 2006, and is available for download from the Google Earth website. With a few exceptions noted below, the Mac version appears to be stable and complete, with virtually all the same functionality as the original Windows version.
Screenshots and an actual binary of the Mac version had been leaked to the Internet a month previously, on December 8, 2005. The leaked version was significantly incomplete. Among other things, neither the Help menu nor its "Display License" feature worked, indicating that this version was intended for Google's internal use only. Google released no statement regarding the leak.
Currently, the Mac version runs only under Mac OS X versions 10.4 and 10.3.9. There is no embedded browser and no direct interface to Gmail. There are a few bugs concerning the menu bar when switching between applications and a few bugs concerning annotation balloons and printing.
The latest version, 4.1.7076.4558, released on May 9, 2007, features, among other things, a new user interface and the option for Mac OS X users to upgrade to the "Plus" version.[14] Some users reported difficulties with Google Earth crashing in the latest version when zooming in.[15]
[edit] Linux version
Google Earth 4(beta) Running on Ubuntu 6.06
Starting with the version 4 beta, Google Earth functions under Linux, as a native port using the Qt-toolkit.
Minimum System Requirements[16]
Kernel: 2.4 or later
CPU: Pentium 3, 500 MHz
System Memory (RAM): 128 MB
Hard Disk: 400 MB free space
Network Speed: 128 kbit/s
Screen: 1024x768, 16 bit color
Tested and works on the following distributions:
Ubuntu 5.10/6.06/6.10/7.04
SUSE 10.1/10.2
Fedora Core 4/5/6/7
Linspire 5.1
Gentoo 2006.0
Debian 3.1/4
Red Hat 9
Slackware 11.0
FreeBSD 6.1/7.0 with Linux Emulation
Arch Linux 0.7.2 Duke
Xandros 3.0.3 Business Edition
Mandriva 2007
Sabayon Linux 3.26
PCLinuxOS 5.0
[edit] Resolution and accuracy
The Isles of Scilly, showing the very low resolution of some islands. The islands (green area) are about 10 km across.
The west side of Gibraltar, tilted view showing the sea rising up the Rock of Gibraltar - claimed altitude of the sea just off the beach at Elliots Memorial, 252 m.
Google Earth is a complex application representing two and three dimensional data, vector data, integer and real numbers, and a variety of geometric projections. The imagery comes from a variety of sources and the processing of the imagery is done both by machine and humans. In addition, there are many terabytes of information from a variety of sources involving many people. As a result, there are bound to be inaccuracies in the data. Google is continuously taking input and improving the existing data.
Most land areas are covered in satellite imagery with a resolution of about 15 m per pixel. Some population centers are also covered by aircraft imagery (orthophotography) with several pixels per meter. Oceans are covered at a much lower resolution, as are a number of islands; most notably, Tórshavn, the capital of the Faroe Islands, and the Isles of Scilly off southwest England, are at a resolution of about 500 m or less. These pictures are provided by Terrametrics.
Google has resolved many inaccuracies in the vector mapping since the original public release of the software, without requiring an update to the program itself. An example of this was the absence from Google Earth's map boundaries of the Nunavut territory in Canada, a territory that had been created on April 1, 1999; this mistake was corrected by one of the data updates in early 2006. Recent updates have also increased the coverage of detailed aerial photography, particularly in certain areas of western Europe, though not including Ireland where imagery remains extremely limited.
Greenland with an odd black line and cut off fire.
An error causing part of Paris to appear as a hill due to the height of the Eiffel Tower.
The images are not all taken at the same time, but are generally current to within three years. Image sets are sometimes not correctly stitched together. Updates to the photographic database can occasionally be noticed when drastic changes take place in the appearance of the landscape, like for example Google Earth's incomplete updates of New Orleans following Hurricane Katrina, or when placemarks appear to shift unexpectedly across the Earth's surface. Though the placemarks have not in fact moved, the imagery is composed and stitched differently. Such an update to London's photography in early 2006 created shifts of 15-20 metres in many areas, noticeable because the resolution is so high.
Place name and road detail vary greatly from place to place. They are most accurate in the North America and Europe, but regular mapping updates are improving coverage elsewhere.
Errors sometimes occur due to the technology used to measure the height of terrain; for example, tall buildings in Adelaide cause one part of the city to be rendered as a small mountain, when it is in fact flat. The height of the Eiffel Tower creates a similar effect in the rendering of Paris. Also, elevations below sea level are presented as sea level; i.e. Salton City, California; Death Valley; and the Dead Sea are all listed as 0 ft when Salton City is approx −200 ft; Death Valley is −286 ft; and the Dead Sea is −1,378 ft.
Where no 3 arc second digital elevation data was available, the three dimensional images covering some areas of high relief are not at all accurate, but most mountain areas are now well mapped. The underlying digital elevation model has been placed 3 arc seconds too far north and up to 3 arc seconds too far west. This means that some steep mountain ridges incorrectly appear to have shadows extending over onto their south facing sides. Some high resolution images have also been misplaced, an example is the image covering Annapurna, which is misplaced by about 12 arc seconds.
The "Measure" function shows that the length of equator is about 40,030.24 km, giving an error of −0.112% compared with the actual value of 40,075.02 km Earth; for the meridional circumference, it shows a length of about 39,963.13 km, also giving an error of −0.112% compared with the actual value of 40,007.86 km.
The Arctic polar ice caps are completely absent from the current version of Google Earth, as are waves in the oceans. The geographic North Pole is found hovering over the Arctic Ocean. There is very low resolution coverage of the Antarctic continent (1m resolution images of some parts of Antarctica were added in June 2007 for the first time). The tiling system produces artifacts near the poles as the tiles become 'infinitely' small and rounding errors accumulate.
Cloud cover and shadows can make it difficult or impossible to see details in some land areas, including the shadow side of mountains.
The atmosphere in Google Earth is greatly exaggerated. Comparisons with actual photographs show the Google Earth atmosphere to be 20 times thicker.[citation needed]
The stars in the background are not random. Google Earth uses a real star map to render the background. [verification needed]
[edit] National security and privacy issues
The software has been criticized by a number of special groups, including national officials, as being an invasion of privacy and even posing a threat to national security. The typical argument is that the software provides information about military or other critical installations that could be used by terrorists. The following is a selection of such concerns:
Former Indian president APJ Abdul Kalam has expressed concern over the availability of high-resolution pictures of sensitive locations in India.[17] Google subsequently agreed to censor such sites.[18]
The Indian Space Research Organisation has said Google Earth poses a security threat to India, and seeks dialogue with Google officials.[19]
The South Korean government has expressed concern that the software offers images of the presidential palace and various military installations that could possibly be used by their hostile neighbor North Korea.[20]
In 2006, one user spotted a large topographical replica in a remote region of China. The model is a small-scale (1/500) version of the Karakoram Mountain Range, currently under the control of China but claimed by India. When later confirmed as a replica of this region, spectators began entertaining military implications.[21][22]
The Area 51 base in the Nevada desert is clearly visible, with no evidence of intentional obstruction or blurring. The base's runways and even a number of planes are visible, but sources confirm that the government has knowledge of all nearby photography satellites, and personnel are instructed to cover any vital technology and stay within the buildings at all times when one is within range.
Morocco's main Internet provider Maroc Telecom has been blocking Google Earth[23] since August 2006 without giving any justification for it.
Operators of the Lucas Heights nuclear reactor in Sydney, New South Wales asked Google to censor high resolution pictures of the facility.[24] However, they later withdrew the request.[25]
In July 2007, it was reported that a new Chinese navy Jin-class nuclear ballistic missile submarine was photographed at the Xiaopingdao Submarine Base south of Dalian[26].
Blurred out image of the Royal Stables in The Hague, Netherlands.
Some citizens may express concerns over aerial information depicting their properties and residences being disseminated freely. As relatively few jurisdictions actually guarantee the individual's right to privacy, as opposed to the state's right to secrecy, this is an evolving, but minor, point. Perhaps aware of these critiques, for a time, Google had Area 51 (which is highly visible and easy to find) in Nevada as a default placemark when Google Earth is first installed.
As a result of pressure from the United States government, the residence of the Vice President at Number One Observatory Circle is obscured through pixelization in Google Earth and Google Maps. The usefulness of this downgrade is questionable, as high-resolution photos and aerial surveys of the property are readily available on the Internet elsewhere.[27] Capitol Hill used to also be pixelized in this way but this was lifted.
Critics have expressed concern over the willingness of Google to cripple their dataset to cater to special interests, believing that intentionally obscuring any land goes against its stated goal of letting the user "point and zoom to any place on the planet that you want to explore".
[edit] Google Earth Community
The Google Earth Community is an online forum[28] which is dedicated to producing placemarks of interesting or educational perspectives. It may be found on the Google Earth webpage or under the Help section on the program itself. After downloading a placemark, it will automatically run Google Earth (if not opened), and fly to the area specified by the person who placed it. Once there, you can add it to your "My Places" by right clicking on the icon and selecting "Save to My Places". Additionally, anyone can post a placemark for others to download; as long as you have an account.
Google earth also can be used to locate "disasters". Currently a user can find these items within the google earth community. An example is a capsized ship off of the shore (69°15′32.22″N 33°14′17.11″E / 69.25895, 33.2380861) or a burning car, on A3 autobahn near Gieslenberg, N of Leverkusen, Germany (51°4′47.04″N 6°59′17.77″E / 51.0797333, 6.9882694).
[edit] Copyright
Currently, every image created from Google Earth using satellite data provided by Google Earth is a copyrighted map. Any derivative from Google Earth is made from copyrighted data which, under United States Copyright Law, may not be used except under the licenses Google provides. Google allows non-commercial personal use of the images (e.g. on a personal website or blog) as long as copyrights and attributions are preserved[29]. By contrast, images created with NASA's globe software World Wind using Blue Marble, Landsat or USGS layer, each of which is a terrain layer in the public domain. Works created by an agency of the United States government are public domain at the moment of creation. This means that those images can be freely modified, re-distributed and used for commercial purposes.
[edit] Google Earth Pro
For a $400 annual subscription fee, Google Earth Pro is a business-oriented upgrade to Google Earth that has more features than the "Plus" version. The Pro version includes add-on software such as:
Movie making.
GIS data importer.
Advanced printing modules.
These used to cost extra in addition to the $400 fee but have recently been included in the package.[30]
[edit] See also
[edit] Related information
Web mapping
Geoweb
NASA World Wind
Yinchuan - subject to an Internet phenomenon originating on Google Earth forum.
[edit] Google mapping services
List of Google services and tools
Google Maps
Google Moon
Google Mars
[edit] Other providers
DigitalGlobe — the provider of high resolution imagery to Google Earth
EarthSat
GeoEye
GlobeXplorer
Pictometry
Spot Image
ViewGL - updated aerial imagery for Google Earth
Saturday, August 25, 2007
GOOGLE EARTH
Formerly known as Earth Viewer, Google Earth was developed by Keyhole, Inc., a company acquired by Google in 2004. The product was renamed Google Earth in 2005 and is currently available for use on personal computers running Microsoft Windows 2000, XP, or Vista; Mac OS X 10.3.9 and above; Linux (released on June 12, 2006); and FreeBSD. In addition to releasing an updated Keyhole based client, Google also added the imagery from the Earth database to their web based mapping software. The release of Google Earth caused a more than tenfold increase in media coverage on virtual globes between 2005 and 2006,[3] driving public interest in geospatial technologies and applications.
Denver, Colorado, viewed in Google Earth, now almost completely modeled with high-quality 3D models.
The viewer will show houses, the color of cars, and even the shadows of people and street signs. The degree of resolution available is based somewhat on the points of interest, but most land (except for some islands) is covered in at least 15 meters of resolution[4]. Las Vegas, Nevada and Cambridge, Massachusetts include examples of the highest resolution, at 15 cm (6 inches). Google Earth allows users to search for addresses (for some countries only), enter coordinates, or simply use the mouse to browse to a location.
Google Earth also has digital elevation model (DEM) data collected by NASA's Shuttle Radar Topography Mission. This means one can view the Grand Canyon or Mount Everest in three dimensions, instead of 2D like other map programs/sites. Since 23 November 2006, the 3D views of many mountains, including Mount Everest, have been improved by the use of supplementary DEM data to fill the gaps in SRTM coverage[5]. In addition, Google has provided a layer allowing one to see 3D buildings for many major cities in the US and Japan.
Many people using the applications are adding their own data and making them available through various sources, such as the BBS or blogs mentioned in the link section below. Google Earth is able to show all kinds of images overlaid on the surface of the earth and is also Web Map Service client.
Google Earth supports managing three-dimensional geospatial data through Keyhole Markup Language (KML). It is available in a free version, and in licensed versions for commercial use.
Downtown Los Angeles, using the 3D Warehouse feature.
Google Earth has the capability to show 3D buildings and structures (such as bridges), which consist of users' submissions using SketchUp, a 3D modeling program. In prior versions of Google Earth (before Version 4), 3D buildings were limited to a few cities, and had poorer rendering with no textures.
Many buildings and structures from around the world now have detailed 3D structures; including (but not limited to) those in the countries, the United States, Canada, India, Japan, United Kingdom,[6] Germany, Pakistan and the cities, Amsterdam and Alexandria[7]. Three-dimensional renderings are available for certain buildings and structures around the world via Google's 3D Warehouse[8] and other websites.
[edit] Sky mode
In version 4.2, released August 22, 2007, Google Earth added a Sky tool for viewing stars and astronomical images.[9] Google Sky is produced by Google through a partnership with the Space Telescope Science Institute in Baltimore, the science operations center for Hubble. Dr. Alberto Conti and his co-developer Dr. Carol Christian of the Space Telescope Science Institute, plan to add the public images from 2007,[10] as well as color images of all of the archived data from Hubble's Advanced Camera for Surveys. Newly released Hubble pictures will be added to the Google Sky program as soon as they are issued. Also visible on Sky mode are constellations, stars, galaxies and animations depicting the planets on their orbits.
[edit] Wikipedia and Panoramio integration
In December 2006 Google Earth added a new layer called "Geographic Web" that includes integration with Wikipedia and Panoramio. In Wikipedia, entries are scraped for coordinates via the Coord templates. If the options to show Wikipedia or Panoramio entries are selected, users will be presented with clickable dots in their current Google Earth view. When any of these dots are selected, the user will be shown the Wikipedia or Panoramio entry right in Google Earth. There is also a community-layer from the project Wikipedia-World. More coordinates are used, different types are in the display and different languages are supported than the built-in Wikipedia layer. See: *dynamic resp. static layer. Google announced on May 30th, 2007 that it is acquiring Panoramio.[11]
[edit] Influences
The Google Earth interface bears a noted similarity to the ‘Earth’ program described in Neal Stephenson’s sci-fi classic Snow Crash. Indeed, a Google Earth co-founder claimed that Google Earth was modeled after Snow Crash, while another co-founder said it was inspired by Powers of Ten.[12]
[edit] Specifications
Google Earth comes with atmosphere effects and seabed
Coordinate System and Projection
The internal coordinate system of Google Earth is geographic coordinates (latitude/longitude) on the World Geodetic System of 1984 (WGS84) datum.
Google Earth shows the earth as it looks from an elevated platform such as an airplane or orbiting satellite. The projection used to achieve this effect is called the General Perspective. This is similar to the Orthographic projection, except that the point of perspective is a finite (near earth) distance rather than an infinite (deep space) distance.[13]
Baseline resolutions
U.S.: 15 m (some states are completely in 1 m or better)
Germany, Switzerland, Netherlands, Denmark, England, Andorra, Luxembourg, Liechtenstein, San Marino, Vatican City: 1 m or better
Global: Generally 15 m (some areas, such as Antarctica, are in extremely low resolution), but this depends on the quality of the satellite/aerial photograph uploaded.
Typical high resolutions
U.S.: 1 m, 0.6 m, 0.3 m, 0.15 m (extremely rare; e.g. Cambridge and Google Campus, or Glendale)
Europe : 0.3 m, 0.15 m (e.g. Berlin, Zürich, Hamburg)
Altitude resolution:
Surface: varies by country
Seabed: Not applicable (a colorscale approximating sea floor depth is "printed" on the spherical surface).
Age: Images are usually less than 3 years old. The date next to the copyright information is often cited as the date the picture was taken, but this practice is incorrect.
Google Earth is unlikely to operate on older hardware configurations. The most recent downloads available document these minimum configurations:
Pentium 3, 500 MHz
128 MB RAM
400 MB free disk space
Network speed: 128 kb/s
16MB 3D-capable graphics card
Resolution of 1024x768, 16-bit High Color
Windows XP or Windows 2000 (not Windows ME compatible), Linux, Mac OS X
The most likely mode of failure is insufficient video RAM: the software is designed to warn the user if their graphics card is not able to support Earth (this often occurs due to insufficient Video RAM or buggy graphics card drivers). The next most likely mode of failure is Internet access speed. Except for the very patient, broadband Internet (Cable, DSL, T1, etc.) is required.
[edit] Mac version
Google Earth (Mac OS X)
A version for Mac OS X was released on January 10, 2006, and is available for download from the Google Earth website. With a few exceptions noted below, the Mac version appears to be stable and complete, with virtually all the same functionality as the original Windows version.
Screenshots and an actual binary of the Mac version had been leaked to the Internet a month previously, on December 8, 2005. The leaked version was significantly incomplete. Among other things, neither the Help menu nor its "Display License" feature worked, indicating that this version was intended for Google's internal use only. Google released no statement regarding the leak.
Currently, the Mac version runs only under Mac OS X versions 10.4 and 10.3.9. There is no embedded browser and no direct interface to Gmail. There are a few bugs concerning the menu bar when switching between applications and a few bugs concerning annotation balloons and printing.
The latest version, 4.1.7076.4558, released on May 9, 2007, features, among other things, a new user interface and the option for Mac OS X users to upgrade to the "Plus" version.[14] Some users reported difficulties with Google Earth crashing in the latest version when zooming in.[15]
[edit] Linux version
Google Earth 4(beta) Running on Ubuntu 6.06
Starting with the version 4 beta, Google Earth functions under Linux, as a native port using the Qt-toolkit.
Minimum System Requirements[16]
Kernel: 2.4 or later
CPU: Pentium 3, 500 MHz
System Memory (RAM): 128 MB
Hard Disk: 400 MB free space
Network Speed: 128 kbit/s
Screen: 1024x768, 16 bit color
Tested and works on the following distributions:
Ubuntu 5.10/6.06/6.10/7.04
SUSE 10.1/10.2
Fedora Core 4/5/6/7
Linspire 5.1
Gentoo 2006.0
Debian 3.1/4
Red Hat 9
Slackware 11.0
FreeBSD 6.1/7.0 with Linux Emulation
Arch Linux 0.7.2 Duke
Xandros 3.0.3 Business Edition
Mandriva 2007
Sabayon Linux 3.26
PCLinuxOS 5.0
[edit] Resolution and accuracy
The Isles of Scilly, showing the very low resolution of some islands. The islands (green area) are about 10 km across.
The west side of Gibraltar, tilted view showing the sea rising up the Rock of Gibraltar - claimed altitude of the sea just off the beach at Elliots Memorial, 252 m.
Google Earth is a complex application representing two and three dimensional data, vector data, integer and real numbers, and a variety of geometric projections. The imagery comes from a variety of sources and the processing of the imagery is done both by machine and humans. In addition, there are many terabytes of information from a variety of sources involving many people. As a result, there are bound to be inaccuracies in the data. Google is continuously taking input and improving the existing data.
Most land areas are covered in satellite imagery with a resolution of about 15 m per pixel. Some population centers are also covered by aircraft imagery (orthophotography) with several pixels per meter. Oceans are covered at a much lower resolution, as are a number of islands; most notably, Tórshavn, the capital of the Faroe Islands, and the Isles of Scilly off southwest England, are at a resolution of about 500 m or less. These pictures are provided by Terrametrics.
Google has resolved many inaccuracies in the vector mapping since the original public release of the software, without requiring an update to the program itself. An example of this was the absence from Google Earth's map boundaries of the Nunavut territory in Canada, a territory that had been created on April 1, 1999; this mistake was corrected by one of the data updates in early 2006. Recent updates have also increased the coverage of detailed aerial photography, particularly in certain areas of western Europe, though not including Ireland where imagery remains extremely limited.
Greenland with an odd black line and cut off fire.
An error causing part of Paris to appear as a hill due to the height of the Eiffel Tower.
The images are not all taken at the same time, but are generally current to within three years. Image sets are sometimes not correctly stitched together. Updates to the photographic database can occasionally be noticed when drastic changes take place in the appearance of the landscape, like for example Google Earth's incomplete updates of New Orleans following Hurricane Katrina, or when placemarks appear to shift unexpectedly across the Earth's surface. Though the placemarks have not in fact moved, the imagery is composed and stitched differently. Such an update to London's photography in early 2006 created shifts of 15-20 metres in many areas, noticeable because the resolution is so high.
Place name and road detail vary greatly from place to place. They are most accurate in the North America and Europe, but regular mapping updates are improving coverage elsewhere.
Errors sometimes occur due to the technology used to measure the height of terrain; for example, tall buildings in Adelaide cause one part of the city to be rendered as a small mountain, when it is in fact flat. The height of the Eiffel Tower creates a similar effect in the rendering of Paris. Also, elevations below sea level are presented as sea level; i.e. Salton City, California; Death Valley; and the Dead Sea are all listed as 0 ft when Salton City is approx −200 ft; Death Valley is −286 ft; and the Dead Sea is −1,378 ft.
Where no 3 arc second digital elevation data was available, the three dimensional images covering some areas of high relief are not at all accurate, but most mountain areas are now well mapped. The underlying digital elevation model has been placed 3 arc seconds too far north and up to 3 arc seconds too far west. This means that some steep mountain ridges incorrectly appear to have shadows extending over onto their south facing sides. Some high resolution images have also been misplaced, an example is the image covering Annapurna, which is misplaced by about 12 arc seconds.
The "Measure" function shows that the length of equator is about 40,030.24 km, giving an error of −0.112% compared with the actual value of 40,075.02 km Earth; for the meridional circumference, it shows a length of about 39,963.13 km, also giving an error of −0.112% compared with the actual value of 40,007.86 km.
The Arctic polar ice caps are completely absent from the current version of Google Earth, as are waves in the oceans. The geographic North Pole is found hovering over the Arctic Ocean. There is very low resolution coverage of the Antarctic continent (1m resolution images of some parts of Antarctica were added in June 2007 for the first time). The tiling system produces artifacts near the poles as the tiles become 'infinitely' small and rounding errors accumulate.
Cloud cover and shadows can make it difficult or impossible to see details in some land areas, including the shadow side of mountains.
The atmosphere in Google Earth is greatly exaggerated. Comparisons with actual photographs show the Google Earth atmosphere to be 20 times thicker.[citation needed]
The stars in the background are not random. Google Earth uses a real star map to render the background. [verification needed]
[edit] National security and privacy issues
The software has been criticized by a number of special groups, including national officials, as being an invasion of privacy and even posing a threat to national security. The typical argument is that the software provides information about military or other critical installations that could be used by terrorists. The following is a selection of such concerns:
Former Indian president APJ Abdul Kalam has expressed concern over the availability of high-resolution pictures of sensitive locations in India.[17] Google subsequently agreed to censor such sites.[18]
The Indian Space Research Organisation has said Google Earth poses a security threat to India, and seeks dialogue with Google officials.[19]
The South Korean government has expressed concern that the software offers images of the presidential palace and various military installations that could possibly be used by their hostile neighbor North Korea.[20]
In 2006, one user spotted a large topographical replica in a remote region of China. The model is a small-scale (1/500) version of the Karakoram Mountain Range, currently under the control of China but claimed by India. When later confirmed as a replica of this region, spectators began entertaining military implications.[21][22]
The Area 51 base in the Nevada desert is clearly visible, with no evidence of intentional obstruction or blurring. The base's runways and even a number of planes are visible, but sources confirm that the government has knowledge of all nearby photography satellites, and personnel are instructed to cover any vital technology and stay within the buildings at all times when one is within range.
Morocco's main Internet provider Maroc Telecom has been blocking Google Earth[23] since August 2006 without giving any justification for it.
Operators of the Lucas Heights nuclear reactor in Sydney, New South Wales asked Google to censor high resolution pictures of the facility.[24] However, they later withdrew the request.[25]
In July 2007, it was reported that a new Chinese navy Jin-class nuclear ballistic missile submarine was photographed at the Xiaopingdao Submarine Base south of Dalian[26].
Blurred out image of the Royal Stables in The Hague, Netherlands.
Some citizens may express concerns over aerial information depicting their properties and residences being disseminated freely. As relatively few jurisdictions actually guarantee the individual's right to privacy, as opposed to the state's right to secrecy, this is an evolving, but minor, point. Perhaps aware of these critiques, for a time, Google had Area 51 (which is highly visible and easy to find) in Nevada as a default placemark when Google Earth is first installed.
As a result of pressure from the United States government, the residence of the Vice President at Number One Observatory Circle is obscured through pixelization in Google Earth and Google Maps. The usefulness of this downgrade is questionable, as high-resolution photos and aerial surveys of the property are readily available on the Internet elsewhere.[27] Capitol Hill used to also be pixelized in this way but this was lifted.
Critics have expressed concern over the willingness of Google to cripple their dataset to cater to special interests, believing that intentionally obscuring any land goes against its stated goal of letting the user "point and zoom to any place on the planet that you want to explore".
[edit] Google Earth Community
The Google Earth Community is an online forum[28] which is dedicated to producing placemarks of interesting or educational perspectives. It may be found on the Google Earth webpage or under the Help section on the program itself. After downloading a placemark, it will automatically run Google Earth (if not opened), and fly to the area specified by the person who placed it. Once there, you can add it to your "My Places" by right clicking on the icon and selecting "Save to My Places". Additionally, anyone can post a placemark for others to download; as long as you have an account.
Google earth also can be used to locate "disasters". Currently a user can find these items within the google earth community. An example is a capsized ship off of the shore (69°15′32.22″N 33°14′17.11″E / 69.25895, 33.2380861) or a burning car, on A3 autobahn near Gieslenberg, N of Leverkusen, Germany (51°4′47.04″N 6°59′17.77″E / 51.0797333, 6.9882694).
[edit] Copyright
Currently, every image created from Google Earth using satellite data provided by Google Earth is a copyrighted map. Any derivative from Google Earth is made from copyrighted data which, under United States Copyright Law, may not be used except under the licenses Google provides. Google allows non-commercial personal use of the images (e.g. on a personal website or blog) as long as copyrights and attributions are preserved[29]. By contrast, images created with NASA's globe software World Wind using Blue Marble, Landsat or USGS layer, each of which is a terrain layer in the public domain. Works created by an agency of the United States government are public domain at the moment of creation. This means that those images can be freely modified, re-distributed and used for commercial purposes.
[edit] Google Earth Pro
For a $400 annual subscription fee, Google Earth Pro is a business-oriented upgrade to Google Earth that has more features than the "Plus" version. The Pro version includes add-on software such as:
Movie making.
GIS data importer.
Advanced printing modules.
These used to cost extra in addition to the $400 fee but have recently been included in the package.[30]
[edit] See also
[edit] Related information
Web mapping
Geoweb
NASA World Wind
Yinchuan - subject to an Internet phenomenon originating on Google Earth forum.
[edit] Google mapping services
List of Google services and tools
Google Maps
Google Moon
Google Mars
[edit] Other providers
DigitalGlobe — the provider of high resolution imagery to Google Earth
EarthSat
GeoEye
GlobeXplorer
Pictometry
Spot Image
ViewGL - updated aerial imagery for Google Earth
Denver, Colorado, viewed in Google Earth, now almost completely modeled with high-quality 3D models.
The viewer will show houses, the color of cars, and even the shadows of people and street signs. The degree of resolution available is based somewhat on the points of interest, but most land (except for some islands) is covered in at least 15 meters of resolution[4]. Las Vegas, Nevada and Cambridge, Massachusetts include examples of the highest resolution, at 15 cm (6 inches). Google Earth allows users to search for addresses (for some countries only), enter coordinates, or simply use the mouse to browse to a location.
Google Earth also has digital elevation model (DEM) data collected by NASA's Shuttle Radar Topography Mission. This means one can view the Grand Canyon or Mount Everest in three dimensions, instead of 2D like other map programs/sites. Since 23 November 2006, the 3D views of many mountains, including Mount Everest, have been improved by the use of supplementary DEM data to fill the gaps in SRTM coverage[5]. In addition, Google has provided a layer allowing one to see 3D buildings for many major cities in the US and Japan.
Many people using the applications are adding their own data and making them available through various sources, such as the BBS or blogs mentioned in the link section below. Google Earth is able to show all kinds of images overlaid on the surface of the earth and is also Web Map Service client.
Google Earth supports managing three-dimensional geospatial data through Keyhole Markup Language (KML). It is available in a free version, and in licensed versions for commercial use.
Downtown Los Angeles, using the 3D Warehouse feature.
Google Earth has the capability to show 3D buildings and structures (such as bridges), which consist of users' submissions using SketchUp, a 3D modeling program. In prior versions of Google Earth (before Version 4), 3D buildings were limited to a few cities, and had poorer rendering with no textures.
Many buildings and structures from around the world now have detailed 3D structures; including (but not limited to) those in the countries, the United States, Canada, India, Japan, United Kingdom,[6] Germany, Pakistan and the cities, Amsterdam and Alexandria[7]. Three-dimensional renderings are available for certain buildings and structures around the world via Google's 3D Warehouse[8] and other websites.
[edit] Sky mode
In version 4.2, released August 22, 2007, Google Earth added a Sky tool for viewing stars and astronomical images.[9] Google Sky is produced by Google through a partnership with the Space Telescope Science Institute in Baltimore, the science operations center for Hubble. Dr. Alberto Conti and his co-developer Dr. Carol Christian of the Space Telescope Science Institute, plan to add the public images from 2007,[10] as well as color images of all of the archived data from Hubble's Advanced Camera for Surveys. Newly released Hubble pictures will be added to the Google Sky program as soon as they are issued. Also visible on Sky mode are constellations, stars, galaxies and animations depicting the planets on their orbits.
[edit] Wikipedia and Panoramio integration
In December 2006 Google Earth added a new layer called "Geographic Web" that includes integration with Wikipedia and Panoramio. In Wikipedia, entries are scraped for coordinates via the Coord templates. If the options to show Wikipedia or Panoramio entries are selected, users will be presented with clickable dots in their current Google Earth view. When any of these dots are selected, the user will be shown the Wikipedia or Panoramio entry right in Google Earth. There is also a community-layer from the project Wikipedia-World. More coordinates are used, different types are in the display and different languages are supported than the built-in Wikipedia layer. See: *dynamic resp. static layer. Google announced on May 30th, 2007 that it is acquiring Panoramio.[11]
[edit] Influences
The Google Earth interface bears a noted similarity to the ‘Earth’ program described in Neal Stephenson’s sci-fi classic Snow Crash. Indeed, a Google Earth co-founder claimed that Google Earth was modeled after Snow Crash, while another co-founder said it was inspired by Powers of Ten.[12]
[edit] Specifications
Google Earth comes with atmosphere effects and seabed
Coordinate System and Projection
The internal coordinate system of Google Earth is geographic coordinates (latitude/longitude) on the World Geodetic System of 1984 (WGS84) datum.
Google Earth shows the earth as it looks from an elevated platform such as an airplane or orbiting satellite. The projection used to achieve this effect is called the General Perspective. This is similar to the Orthographic projection, except that the point of perspective is a finite (near earth) distance rather than an infinite (deep space) distance.[13]
Baseline resolutions
U.S.: 15 m (some states are completely in 1 m or better)
Germany, Switzerland, Netherlands, Denmark, England, Andorra, Luxembourg, Liechtenstein, San Marino, Vatican City: 1 m or better
Global: Generally 15 m (some areas, such as Antarctica, are in extremely low resolution), but this depends on the quality of the satellite/aerial photograph uploaded.
Typical high resolutions
U.S.: 1 m, 0.6 m, 0.3 m, 0.15 m (extremely rare; e.g. Cambridge and Google Campus, or Glendale)
Europe : 0.3 m, 0.15 m (e.g. Berlin, Zürich, Hamburg)
Altitude resolution:
Surface: varies by country
Seabed: Not applicable (a colorscale approximating sea floor depth is "printed" on the spherical surface).
Age: Images are usually less than 3 years old. The date next to the copyright information is often cited as the date the picture was taken, but this practice is incorrect.
Google Earth is unlikely to operate on older hardware configurations. The most recent downloads available document these minimum configurations:
Pentium 3, 500 MHz
128 MB RAM
400 MB free disk space
Network speed: 128 kb/s
16MB 3D-capable graphics card
Resolution of 1024x768, 16-bit High Color
Windows XP or Windows 2000 (not Windows ME compatible), Linux, Mac OS X
The most likely mode of failure is insufficient video RAM: the software is designed to warn the user if their graphics card is not able to support Earth (this often occurs due to insufficient Video RAM or buggy graphics card drivers). The next most likely mode of failure is Internet access speed. Except for the very patient, broadband Internet (Cable, DSL, T1, etc.) is required.
[edit] Mac version
Google Earth (Mac OS X)
A version for Mac OS X was released on January 10, 2006, and is available for download from the Google Earth website. With a few exceptions noted below, the Mac version appears to be stable and complete, with virtually all the same functionality as the original Windows version.
Screenshots and an actual binary of the Mac version had been leaked to the Internet a month previously, on December 8, 2005. The leaked version was significantly incomplete. Among other things, neither the Help menu nor its "Display License" feature worked, indicating that this version was intended for Google's internal use only. Google released no statement regarding the leak.
Currently, the Mac version runs only under Mac OS X versions 10.4 and 10.3.9. There is no embedded browser and no direct interface to Gmail. There are a few bugs concerning the menu bar when switching between applications and a few bugs concerning annotation balloons and printing.
The latest version, 4.1.7076.4558, released on May 9, 2007, features, among other things, a new user interface and the option for Mac OS X users to upgrade to the "Plus" version.[14] Some users reported difficulties with Google Earth crashing in the latest version when zooming in.[15]
[edit] Linux version
Google Earth 4(beta) Running on Ubuntu 6.06
Starting with the version 4 beta, Google Earth functions under Linux, as a native port using the Qt-toolkit.
Minimum System Requirements[16]
Kernel: 2.4 or later
CPU: Pentium 3, 500 MHz
System Memory (RAM): 128 MB
Hard Disk: 400 MB free space
Network Speed: 128 kbit/s
Screen: 1024x768, 16 bit color
Tested and works on the following distributions:
Ubuntu 5.10/6.06/6.10/7.04
SUSE 10.1/10.2
Fedora Core 4/5/6/7
Linspire 5.1
Gentoo 2006.0
Debian 3.1/4
Red Hat 9
Slackware 11.0
FreeBSD 6.1/7.0 with Linux Emulation
Arch Linux 0.7.2 Duke
Xandros 3.0.3 Business Edition
Mandriva 2007
Sabayon Linux 3.26
PCLinuxOS 5.0
[edit] Resolution and accuracy
The Isles of Scilly, showing the very low resolution of some islands. The islands (green area) are about 10 km across.
The west side of Gibraltar, tilted view showing the sea rising up the Rock of Gibraltar - claimed altitude of the sea just off the beach at Elliots Memorial, 252 m.
Google Earth is a complex application representing two and three dimensional data, vector data, integer and real numbers, and a variety of geometric projections. The imagery comes from a variety of sources and the processing of the imagery is done both by machine and humans. In addition, there are many terabytes of information from a variety of sources involving many people. As a result, there are bound to be inaccuracies in the data. Google is continuously taking input and improving the existing data.
Most land areas are covered in satellite imagery with a resolution of about 15 m per pixel. Some population centers are also covered by aircraft imagery (orthophotography) with several pixels per meter. Oceans are covered at a much lower resolution, as are a number of islands; most notably, Tórshavn, the capital of the Faroe Islands, and the Isles of Scilly off southwest England, are at a resolution of about 500 m or less. These pictures are provided by Terrametrics.
Google has resolved many inaccuracies in the vector mapping since the original public release of the software, without requiring an update to the program itself. An example of this was the absence from Google Earth's map boundaries of the Nunavut territory in Canada, a territory that had been created on April 1, 1999; this mistake was corrected by one of the data updates in early 2006. Recent updates have also increased the coverage of detailed aerial photography, particularly in certain areas of western Europe, though not including Ireland where imagery remains extremely limited.
Greenland with an odd black line and cut off fire.
An error causing part of Paris to appear as a hill due to the height of the Eiffel Tower.
The images are not all taken at the same time, but are generally current to within three years. Image sets are sometimes not correctly stitched together. Updates to the photographic database can occasionally be noticed when drastic changes take place in the appearance of the landscape, like for example Google Earth's incomplete updates of New Orleans following Hurricane Katrina, or when placemarks appear to shift unexpectedly across the Earth's surface. Though the placemarks have not in fact moved, the imagery is composed and stitched differently. Such an update to London's photography in early 2006 created shifts of 15-20 metres in many areas, noticeable because the resolution is so high.
Place name and road detail vary greatly from place to place. They are most accurate in the North America and Europe, but regular mapping updates are improving coverage elsewhere.
Errors sometimes occur due to the technology used to measure the height of terrain; for example, tall buildings in Adelaide cause one part of the city to be rendered as a small mountain, when it is in fact flat. The height of the Eiffel Tower creates a similar effect in the rendering of Paris. Also, elevations below sea level are presented as sea level; i.e. Salton City, California; Death Valley; and the Dead Sea are all listed as 0 ft when Salton City is approx −200 ft; Death Valley is −286 ft; and the Dead Sea is −1,378 ft.
Where no 3 arc second digital elevation data was available, the three dimensional images covering some areas of high relief are not at all accurate, but most mountain areas are now well mapped. The underlying digital elevation model has been placed 3 arc seconds too far north and up to 3 arc seconds too far west. This means that some steep mountain ridges incorrectly appear to have shadows extending over onto their south facing sides. Some high resolution images have also been misplaced, an example is the image covering Annapurna, which is misplaced by about 12 arc seconds.
The "Measure" function shows that the length of equator is about 40,030.24 km, giving an error of −0.112% compared with the actual value of 40,075.02 km Earth; for the meridional circumference, it shows a length of about 39,963.13 km, also giving an error of −0.112% compared with the actual value of 40,007.86 km.
The Arctic polar ice caps are completely absent from the current version of Google Earth, as are waves in the oceans. The geographic North Pole is found hovering over the Arctic Ocean. There is very low resolution coverage of the Antarctic continent (1m resolution images of some parts of Antarctica were added in June 2007 for the first time). The tiling system produces artifacts near the poles as the tiles become 'infinitely' small and rounding errors accumulate.
Cloud cover and shadows can make it difficult or impossible to see details in some land areas, including the shadow side of mountains.
The atmosphere in Google Earth is greatly exaggerated. Comparisons with actual photographs show the Google Earth atmosphere to be 20 times thicker.[citation needed]
The stars in the background are not random. Google Earth uses a real star map to render the background. [verification needed]
[edit] National security and privacy issues
The software has been criticized by a number of special groups, including national officials, as being an invasion of privacy and even posing a threat to national security. The typical argument is that the software provides information about military or other critical installations that could be used by terrorists. The following is a selection of such concerns:
Former Indian president APJ Abdul Kalam has expressed concern over the availability of high-resolution pictures of sensitive locations in India.[17] Google subsequently agreed to censor such sites.[18]
The Indian Space Research Organisation has said Google Earth poses a security threat to India, and seeks dialogue with Google officials.[19]
The South Korean government has expressed concern that the software offers images of the presidential palace and various military installations that could possibly be used by their hostile neighbor North Korea.[20]
In 2006, one user spotted a large topographical replica in a remote region of China. The model is a small-scale (1/500) version of the Karakoram Mountain Range, currently under the control of China but claimed by India. When later confirmed as a replica of this region, spectators began entertaining military implications.[21][22]
The Area 51 base in the Nevada desert is clearly visible, with no evidence of intentional obstruction or blurring. The base's runways and even a number of planes are visible, but sources confirm that the government has knowledge of all nearby photography satellites, and personnel are instructed to cover any vital technology and stay within the buildings at all times when one is within range.
Morocco's main Internet provider Maroc Telecom has been blocking Google Earth[23] since August 2006 without giving any justification for it.
Operators of the Lucas Heights nuclear reactor in Sydney, New South Wales asked Google to censor high resolution pictures of the facility.[24] However, they later withdrew the request.[25]
In July 2007, it was reported that a new Chinese navy Jin-class nuclear ballistic missile submarine was photographed at the Xiaopingdao Submarine Base south of Dalian[26].
Blurred out image of the Royal Stables in The Hague, Netherlands.
Some citizens may express concerns over aerial information depicting their properties and residences being disseminated freely. As relatively few jurisdictions actually guarantee the individual's right to privacy, as opposed to the state's right to secrecy, this is an evolving, but minor, point. Perhaps aware of these critiques, for a time, Google had Area 51 (which is highly visible and easy to find) in Nevada as a default placemark when Google Earth is first installed.
As a result of pressure from the United States government, the residence of the Vice President at Number One Observatory Circle is obscured through pixelization in Google Earth and Google Maps. The usefulness of this downgrade is questionable, as high-resolution photos and aerial surveys of the property are readily available on the Internet elsewhere.[27] Capitol Hill used to also be pixelized in this way but this was lifted.
Critics have expressed concern over the willingness of Google to cripple their dataset to cater to special interests, believing that intentionally obscuring any land goes against its stated goal of letting the user "point and zoom to any place on the planet that you want to explore".
[edit] Google Earth Community
The Google Earth Community is an online forum[28] which is dedicated to producing placemarks of interesting or educational perspectives. It may be found on the Google Earth webpage or under the Help section on the program itself. After downloading a placemark, it will automatically run Google Earth (if not opened), and fly to the area specified by the person who placed it. Once there, you can add it to your "My Places" by right clicking on the icon and selecting "Save to My Places". Additionally, anyone can post a placemark for others to download; as long as you have an account.
Google earth also can be used to locate "disasters". Currently a user can find these items within the google earth community. An example is a capsized ship off of the shore (69°15′32.22″N 33°14′17.11″E / 69.25895, 33.2380861) or a burning car, on A3 autobahn near Gieslenberg, N of Leverkusen, Germany (51°4′47.04″N 6°59′17.77″E / 51.0797333, 6.9882694).
[edit] Copyright
Currently, every image created from Google Earth using satellite data provided by Google Earth is a copyrighted map. Any derivative from Google Earth is made from copyrighted data which, under United States Copyright Law, may not be used except under the licenses Google provides. Google allows non-commercial personal use of the images (e.g. on a personal website or blog) as long as copyrights and attributions are preserved[29]. By contrast, images created with NASA's globe software World Wind using Blue Marble, Landsat or USGS layer, each of which is a terrain layer in the public domain. Works created by an agency of the United States government are public domain at the moment of creation. This means that those images can be freely modified, re-distributed and used for commercial purposes.
[edit] Google Earth Pro
For a $400 annual subscription fee, Google Earth Pro is a business-oriented upgrade to Google Earth that has more features than the "Plus" version. The Pro version includes add-on software such as:
Movie making.
GIS data importer.
Advanced printing modules.
These used to cost extra in addition to the $400 fee but have recently been included in the package.[30]
[edit] See also
[edit] Related information
Web mapping
Geoweb
NASA World Wind
Yinchuan - subject to an Internet phenomenon originating on Google Earth forum.
[edit] Google mapping services
List of Google services and tools
Google Maps
Google Moon
Google Mars
[edit] Other providers
DigitalGlobe — the provider of high resolution imagery to Google Earth
EarthSat
GeoEye
GlobeXplorer
Pictometry
Spot Image
ViewGL - updated aerial imagery for Google Earth
Monday, August 13, 2007
Radio Activity And Various Radiations
Radioactivity, spontaneous disintegration of atomic nuclei by the emission of subatomic particles called alpha particles and beta particles, or of electromagnetic rays called X rays and gamma rays. The phenomenon was discovered in 1896 by the French physicist Antoine Henri Becquerel when he observed that the element uranium can blacken a photographic plate, although separated from it by glass or black paper. He also observed that the rays that produce the darkening are capable of discharging an electroscope, indicating that the rays possess an electric charge. In 1898 the French chemists Marie Curie and Pierre Curie deduced that radioactivity is a phenomenon associated with atoms, independent of their physical or chemical state. They also deduced that because the uranium-containing ore pitchblende is more intensely radioactive than the uranium salts that were used by Becquerel, other radioactive elements must be in the ore. They carried through a series of chemical treatments of the pitchblende that resulted in the discovery of two new radioactive elements, polonium and radium. Marie Curie also discovered that the element thorium is radioactive, and in 1899 the radioactive element actinium was discovered by the French chemist André Louis Debierne. In that same year the discovery of the radioactive gas radon was made by the British physicists Ernest Rutherford and Frederick Soddy, who observed it in association with thorium, actinium, and radium.
Pierre Curie French physicist Pierre Curie won the 1903 Nobel Prize in physics for his discovery of radioactive elements. © The Nobel Foundation Radioactivity was soon recognized as a more concentrated source of energy than had been known before. The Curies measured the heat associated with the decay of radium and established that 1 g (0.035 oz) of radium gives off about 100 cal of energy every hour. This heating effect continues hour after hour and year after year, whereas the complete combustion of a gram of coal results in the production of a total of only about 8000 cal of energy. Radioactivity attracted the attention of scientists throughout the world following these early discoveries. In the ensuing decades many aspects of the phenomenon were thoroughly investigated.
sidebar SIDEBAR Thyroid Cancers Linked to Atomic Bomb Tests During the 1940s and 1950s the United States government conducted above-ground nuclear bomb tests in Nevada. In 1982 Congress directed the National Cancer Institute (NCI) to investigate the health effects of radioactive fallout from those tests. The study was the most comprehensive look ever at radioactive exposure. It took 14 years to complete: 100,000 pages of data, statistics, and research were finally compiled into a 1000-page report. The results, which focus on the correlation between milk consumption and thyroid cancer, are summarized in this article from the 1997 Encarta Yearbook. open sidebar
II TYPES OF RADIATIONS
Alpha Particles Alpha particles consist of two protons and two neutrons that act as a single particle. An alpha particle is identical to the nucleus of a Helium atom. When alpha particles are emitted from an unstable radioactive nucleus, the atom is transmuted into a different element.© Microsoft Corporation. All Rights Reserved. Expand
Gamma Rays Gamma rays, or high energy photons, are emitted from the nucleus of an atom when it undergoes radioactive decay. The energy of the gamma ray accounts for the difference in energy between the original nucleus and the decay products. Gamma rays typically can have about the same energy as a high energy X ray. Each radioactive isotope has a characteristic gamma-ray energy.© Microsoft Corporation. All Rights Reserved. Expand
Beta Decay Beta decay can occur in two ways. As shown on the left, a neutron turns into a proton by emitting an antineutrino and a negatively charged beta particle. As shown on the right, a proton turns into a neutron by emitting a neutrino and a positively charged beta particle. Positive beta particles are called positrons and negative beta particles are called electrons. After the decay, the nucleus of the atom contains either one less or one more proton. Beta decay changes an atom of one element into an atom of a new element.© Microsoft Corporation. All Rights Reserved. Expand Rutherford discovered that at least two components are present in the radioactive radiations: alpha particles, which penetrate into aluminum only a few thousandths of a centimeter, and beta particles, which are nearly 100 times more penetrating. Subsequent experiments in which radioactive radiations were subjected to magnetic and electric fields revealed the presence of a third component, gamma rays, which were found to be much more penetrating than beta particles. In an electric field the path of the beta particles is greatly deflected toward the positive electric pole, that of the alpha particles to a lesser extent toward the negative pole, and gamma rays are not deflected at all. Therefore, the beta particles are negatively charged, the alpha particles are positively charged and are heavier than beta particles, and the gamma rays are uncharged.
dynamic timeline Radioactivity Discovered
The discovery that radium decayed to produce radon proved conclusively that radioactive decay is accompanied by a change in the chemical nature of the decaying element. Experiments on the deflection of alpha particles in an electric field showed that the ratio of electric charge to mass of these particles is about twice that of the hydrogen ion. Physicists supposed that the particles could be doubly charged ions of helium (helium atoms with two electrons removed). This supposition was proved by Rutherford when he allowed an alpha-emitting substance to decay near an evacuated thin-glass vessel. The alpha particles were able to penetrate the glass and were then trapped in the vessel, and within a few days the presence of elemental helium was demonstrated by use of a spectroscope. Beta particles were subsequently shown to be electrons, and gamma rays to consist of electromagnetic radiation of the same nature as X rays but of considerably greater energy.
A The Nuclear Hypothesis
In 1911 Rutherford proved the existence of a nucleus within the atom by experiments with alpha particles.
At the time of the discovery of radioactivity physicists believed that the atom was the ultimate, indivisible building block of matter. The recognition of alpha and beta particles as discrete units of matter and of radioactivity as a process by means of which atoms are transformed into new kinds of atoms possessing new chemical properties because of the emission of one or the other of these particles brought with it the realization that atoms themselves must have structure and that they are not the ultimate, fundamental particles of nature. In 1911 Rutherford proved the existence of a nucleus within the atom by experiments in which alpha particles were scattered by thin metal foils (see Atom). The nuclear hypothesis has since grown into a refined and fully accepted theory of atomic structure, in terms of which the entire phenomenon of radioactivity can be explained. Briefly, the atom is thought to consist of a dense central nucleus surrounded by a cloud of electrons. The nucleus, in turn, is composed of protons equal in number to the electrons (in an electrically neutral atom), and neutrons. An alpha particle, or doubly charged helium ion, consists of two neutrons and two protons, and hence can be emitted only from the nucleus of an atom. Loss of an alpha particle by a nucleus results in the formation of a new nucleus, lighter than the original by four mass units (the masses of the neutron and of the proton are about one unit each). An atom of the uranium isotope of mass 238, upon emitting an alpha particle, becomes an atom of another element of mass 234. Each of the two protons that form part of the alpha particle emitted from an atom of uranium-238 possesses a unit of positive electric charge. The number of positive charges in the nucleus, balanced by the same number of negative electrons in the orbits outside the nucleus, determines the chemical nature of the atom. Because the charge on the uranium-238 nucleus decreases by two units as a result of alpha emission, the atomic number of the resultant atom is 2 less than that of the original, which was 92. The new atom has an atomic number of 90 and hence is an isotope of the element thorium. See Elements, Chemical; Nuclear Chemistry; Periodic Law.
web center Ä Find the best online information about Radioactivity. Encarta Editors' PicksHow Nuclear Radiation Works more...
Thorium-234 emits beta particles, which are electrons. According to current theory, beta emission is accomplished by the transformation of a neutron into a proton, thus resulting in an increase in nuclear charge (or atomic number) of one unit. The mass of the electron is negligible, thus the isotope that results from thorium-234 decay has mass number 234 but atomic number 91 and is, therefore, a protactinium isotope.
B Gamma Radiation
Gamma emission is usually found in association with alpha and beta emission. Gamma rays possess no charge or mass; thus emission of gamma rays by a nucleus does not result in a change in chemical properties of the nucleus but merely in the loss of a certain amount of radiant energy. The emission of gamma rays is a compensation by the atomic nucleus for the unstable state that follows alpha and beta processes in the nucleus. The primary alpha or beta particle and its consequent gamma ray are emitted almost simultaneously. A few cases are known of pure alpha and beta emission, however, that is, alpha and beta processes unaccompanied by gamma rays; a number of pure gamma-emitting isotopes are also known. Pure gamma emission occurs when an isotope exists in two different forms, called nuclear isomers, having identical atomic numbers and mass numbers, but different in nuclear-energy content. The emission of gamma rays accompanies the transition of the higher-energy isomer to the lower-energy form. An example of isomerism is the isotope protactinium-234, which exists in two distinct energy states with the emission of gamma rays signaling the transition from one to the other.
Alpha, beta, and gamma radiations are all ejected from their parent nuclei at tremendous speeds. Alpha particles are slowed down and stopped as they pass through matter, primarily through interaction with the electrons present in that matter. Furthermore, most of the alpha particles emitted from the same substance are ejected at very nearly the same velocity. Thus nearly all the alpha particles from polonium-210 travel 3.8 cm through air before being completely stopped, and those of polonium-212 travel 8.5 cm under the same conditions. Measurement of distance traveled by alpha particles is used to identify isotopes. Beta particles are ejected at much greater speeds than alpha particles, and thus will penetrate considerably more matter, although the mechanism by means of which they are stopped is essentially similar. Unlike alpha particles, however, beta particles are emitted at many different speeds, and beta emitters must be distinguished from one another through the existence of the characteristic maximum and average speeds of their beta particles. The distribution in the beta-particle energies (speeds) necessitates the hypothesis of the existence of an uncharged, massless particle called the neutrino, and neutrino emission is now thought to accompany all beta decays. Gamma rays have ranges several times greater than those of beta particles and can in some cases pass through several inches of lead. Alpha and beta particles, when passing through matter, cause the formation of many ions; this ionization is particularly easy to observe when the matter is gaseous. Gamma rays are not charged, and hence cannot cause such ionization directly, but when they interact with matter they cause the ejection of electrons from atoms; the atoms minus some of their electrons are thereby ionized (see Radiation Effects, Biological). Beta rays produce t to z of the ionization generated by alpha rays per centimeter of their path in air. Gamma rays produce about t of the ionization of beta rays. The Geiger-Müller counter and other ionization chambers (see Particle Detectors), which are based on these principles, are used to detect the amounts of individual alpha, beta, and gamma rays, and hence the absolute rates of decay of radioactive substances. One unit of radioactivity, the curie, is based on the decay rate of radium-226, which is 37 billion disintegrations per second. The newer and preferred unit for measuring radioactivity in the International System of Units is called the becquerel. It is equal to one disintegration per second.
Modes of radioactive decay, other than the three above mentioned, exist. Some isotopes are capable of emitting positrons, which are identical with electrons but opposite in charge. The positron-emission process is usually classified as a beta decay and is termed beta-plus emission to distinguish it from the more common negative-electron emission. Positron emission is thought to be accomplished through the conversion, in the nucleus, of a proton into a neutron, resulting in a decrease of the atomic number by one unit. Another mode of decay, known as K-electron capture, consists of the capture of an electron by the nucleus, followed by the transformation of a proton to a neutron. The net result is thus also a decrease of the atomic number by one unit. The process is observable only because the removal of the electron from its orbit results in the emission of an X ray. In recent years it has been shown that a number of isotopes, notably uranium-235 and several isotopes of the artificial transuranium elements, are capable of decaying by a spontaneous-fission process, in which the nucleus is split into two fragments. In the mid-1980s a unique decay mode was observed, in which isotopes of radium of masses 222, 223, and 224 emit carbon-14 nuclei rather than decaying in the usual way by emitting alpha radiation.
III HALF-LIFE
The decay of some substances, such as uranium-238 and thorium-232, appears to continue indefinitely without detectable diminution of the decay rate per unit mass of the isotope (specific-decay rate). Other radioactive substances show a marked decrease in specific-decay rate with time. Among these is the isotope thorium-234 (originally called uranium X), which, after isolation from uranium, decays to half its original radioactive intensity within 25 days. Each individual radioactive substance has a characteristic decay period or half-life; because their half-lives are so long that decay is not appreciable within the observation period, the diminution of the specific-decay rate of some isotopes is not observable under present methods. Thorium-232, for example, has a half-life of 14 billion years.
IV RADIOACTIVE DECAY SERIES
The uranium-radium [decay] series continues until a nonradioactive isotope of lead is reached.
When uranium-238 decays by alpha emission, thorium-234 is formed; thorium-234 is a beta emitter and decays to form protactinium-234. Protactinium-234 in turn is a beta emitter, forming a new isotope of uranium, uranium-234. Uranium-234 decays by alpha emission to form thorium-230, which decays in turn by alpha emission to yield the predominant isotope, radium-226. This radioactive decay series, called the uranium-radium series, continues similarly through five more alpha emissions and four more beta emissions until the end product, a nonradioactive (stable) isotope of lead (element 82) of mass 206 is reached. Every element in the periodic table between uranium and lead is represented in this series, and each isotope is distinguishable by its characteristic half-life. The members of the series all share a common characteristic: Their mass numbers can be made exactly divisible by four if the number 2 is subtracted from them, that is, their mass numbers can be expressed by the simple formula 4n + 2, in which n is a whole number. Other natural radioactive series are the thorium series, called the 4n series, because the mass numbers of all its members are exactly divisible by four, and the actinium series, or 4n + 3 series. The parent of the thorium series is the isotope thorium-232, and its final product is the stable isotope lead-208. The actinium series begins with uranium-235 (named actinouranium by early investigators) and ends with lead-207. A fourth series, the 4n + 1 series, all the members of which are artificially radioactive, has in recent years been discovered and thoroughly characterized. Its initial member is an isotope of the synthetic element curium, curium-241. It contains the longest-lived isotope of the element neptunium, and its final product is bismuth-209.
An interesting application of knowledge of radioactive elements is made in determining the age of the earth. One method of determining geologic time is based on the fact that in many uranium and thorium ores, all of which have been decaying since their formation, the alpha particles have been trapped (as helium atoms) in the interior of the rock. By accurately determining the relative amounts of helium, uranium, and thorium in the rock, the length of time during which the decay processes have been going on (the age of the rock) can be calculated. Another method is based on the determination of the ratio of uranium-238 to lead-206 or of thorium-232 to lead-208 in the rocks (that is, the ratios of concentration of the initial and final members of the decay series). These and other methods give values for the age of the earth of between 3 billion and 5 billion years. Similar values are obtained for meteorites that have fallen to the surface of the earth, as well as samples of the moon brought back by Apollo 11 in July 1969, indicating the possibility that the entire solar system could be about the same age as the earth.
V ARTIFICIAL RADIOACTIVITY
sidebar SCIENTIFIC DISCOVERIES The Discovery of Fission German chemist and Nobel laureate Otto Hahn and Austrian-Swedish physicist Lise Meitner are credited with roles in discovering nuclear fission, the process of splitting an atom into two or more smaller parts. By the 1930s, Hahn and Meitner had experimented with radioactive materials for some time. After Meitner left Germany in 1938, Hahn and German chemist Fritz Strassmann made a breakthrough in their experimentation methods that enabled them to collect physical data showing that an atom of uranium would “burst” under certain conditions. They announced their finding in 1939. Shortly thereafter, Meitner and British physicist Otto Robert Frisch published a paper that provided a theoretical explanation for the process, and named it “fission.” This article by Hahn, which appeared in Scientific American in 1958, describes how, through a number of twists and turns in the road, he and his colleagues discovered the fission process in uranium. open sidebar
All the naturally occurring isotopes above bismuth in the periodic table are radioactive and in addition naturally radioactive isotopes of bismuth, thalium, vanadium, indium, neodymium, gadolinium, hafnium, platinum, lead, rhenium, lutetium, rubidium, potassium, hydrogen, carbon, lanthanum, and samarium exist. In 1919 Rutherford carried out the first nuclear reaction when he bombarded ordinary nitrogen gas (nitrogen-14) with alpha particles and found that the nitrogen nuclei captured alpha particles and emitted protons very rapidly, forming a stable isotope of oxygen, oxygen-17. This reaction can be written symbolically as
¨N + ¸He →©O + §Hin which the atomic numbers of the participating nuclei are conventionally written below and to the left of the chemical symbols and their mass numbers above and to the left. In the above reaction the alpha particle is shown as a helium nucleus and the proton as a hydrogen nucleus.
Not until 1933 was it demonstrated that such nuclear reactions could sometimes result in the formation of new radioactive nuclei. The French chemists Irène and Frédéric Joliot-Curie prepared the first artificially radioactive substance in that year when they bombarded aluminum with alpha particles. The aluminum nuclei captured alpha particles and then emitted neutrons with the consequent formation of an isotope of phosphorus, which decayed by positron emission with a short half-life. They also produced an isotope of nitrogen from boron and one of aluminum from magnesium. Since that time a great many nuclear reactions have been discovered, and the nuclei of elements throughout the periodic table have been bombarded with different particles, including alpha particles, protons, neutrons, and deuterons (ions of the hydrogen isotope of mass 2). As a result of this intensive investigation, more than 400 artificial radioactivities are now known. This research has been aided immeasurably by the development of particle accelerators that accelerate the bombarding particles to enormous speeds, thus in many cases increasing the probability of their capture by the target nuclei.
The vigorous investigation of nuclear reactions and the search for new artificial radioactivities, especially in connection with the search for such activities among the heavier elements, was responsible for the discovery of nuclear fission and the subsequent development of the atomic bomb (see Nuclear Energy; Nuclear Weapons). The investigations have also resulted in the discovery of several new elements that do not exist in nature. The development of nuclear reactors has made possible the production on a large scale of radioactive isotopes of nearly all the elements of the periodic table, and the availability of these isotopes is an incalculable aid to chemical research and to biological and medical research (see Isotopic Tracers). Of great importance among the artificially produced radioactive isotopes is an isotope of carbon, carbon-14, which has a half-life of about 5730 ± 40 years. The availability of this substance has made possible the investigation of numerous aspects of life processes, such as the process of photosynthesis, in a more fundamental manner than hitherto considered possible.
Estimates of the ages of objects such as bones and mummies have been made by carbon-14 measurements.
Scientists have recently shown that a very minute but unchanging amount of carbon-14 is present in the atmosphere of the earth and that all living organisms assimilate traces of this isotope during their lifetime. After death this assimilation ceases and the radioactive carbon, constantly decaying, is no longer maintained at a steady concentration. Estimation of the ages of a number of objects, such as bones and mummies, of historical and archaeological interest have been made possible by carbon-14 measurements. See Dating Methods.
further reading These sources provide additional information on Radioactivity.
In neutron-activation analysis, a sample of a substance is made radioactive in a nuclear reactor. A number of impurities that cannot be detected by other means can then be found by detecting the particular types of radioactivity that are associated with radioisotopes of these impurities. Other applications of radioactive isotopes are in medical therapy, industrial radiography, and specific devices such as phosphorescent light sources, static eliminators, thickness gauges, and nuclear batteries
© 1993-2003 Microsoft Corporation. All rights reserved.
Pierre Curie French physicist Pierre Curie won the 1903 Nobel Prize in physics for his discovery of radioactive elements. © The Nobel Foundation Radioactivity was soon recognized as a more concentrated source of energy than had been known before. The Curies measured the heat associated with the decay of radium and established that 1 g (0.035 oz) of radium gives off about 100 cal of energy every hour. This heating effect continues hour after hour and year after year, whereas the complete combustion of a gram of coal results in the production of a total of only about 8000 cal of energy. Radioactivity attracted the attention of scientists throughout the world following these early discoveries. In the ensuing decades many aspects of the phenomenon were thoroughly investigated.
sidebar SIDEBAR Thyroid Cancers Linked to Atomic Bomb Tests During the 1940s and 1950s the United States government conducted above-ground nuclear bomb tests in Nevada. In 1982 Congress directed the National Cancer Institute (NCI) to investigate the health effects of radioactive fallout from those tests. The study was the most comprehensive look ever at radioactive exposure. It took 14 years to complete: 100,000 pages of data, statistics, and research were finally compiled into a 1000-page report. The results, which focus on the correlation between milk consumption and thyroid cancer, are summarized in this article from the 1997 Encarta Yearbook. open sidebar
II TYPES OF RADIATIONS
Alpha Particles Alpha particles consist of two protons and two neutrons that act as a single particle. An alpha particle is identical to the nucleus of a Helium atom. When alpha particles are emitted from an unstable radioactive nucleus, the atom is transmuted into a different element.© Microsoft Corporation. All Rights Reserved. Expand
Gamma Rays Gamma rays, or high energy photons, are emitted from the nucleus of an atom when it undergoes radioactive decay. The energy of the gamma ray accounts for the difference in energy between the original nucleus and the decay products. Gamma rays typically can have about the same energy as a high energy X ray. Each radioactive isotope has a characteristic gamma-ray energy.© Microsoft Corporation. All Rights Reserved. Expand
Beta Decay Beta decay can occur in two ways. As shown on the left, a neutron turns into a proton by emitting an antineutrino and a negatively charged beta particle. As shown on the right, a proton turns into a neutron by emitting a neutrino and a positively charged beta particle. Positive beta particles are called positrons and negative beta particles are called electrons. After the decay, the nucleus of the atom contains either one less or one more proton. Beta decay changes an atom of one element into an atom of a new element.© Microsoft Corporation. All Rights Reserved. Expand Rutherford discovered that at least two components are present in the radioactive radiations: alpha particles, which penetrate into aluminum only a few thousandths of a centimeter, and beta particles, which are nearly 100 times more penetrating. Subsequent experiments in which radioactive radiations were subjected to magnetic and electric fields revealed the presence of a third component, gamma rays, which were found to be much more penetrating than beta particles. In an electric field the path of the beta particles is greatly deflected toward the positive electric pole, that of the alpha particles to a lesser extent toward the negative pole, and gamma rays are not deflected at all. Therefore, the beta particles are negatively charged, the alpha particles are positively charged and are heavier than beta particles, and the gamma rays are uncharged.
dynamic timeline Radioactivity Discovered
The discovery that radium decayed to produce radon proved conclusively that radioactive decay is accompanied by a change in the chemical nature of the decaying element. Experiments on the deflection of alpha particles in an electric field showed that the ratio of electric charge to mass of these particles is about twice that of the hydrogen ion. Physicists supposed that the particles could be doubly charged ions of helium (helium atoms with two electrons removed). This supposition was proved by Rutherford when he allowed an alpha-emitting substance to decay near an evacuated thin-glass vessel. The alpha particles were able to penetrate the glass and were then trapped in the vessel, and within a few days the presence of elemental helium was demonstrated by use of a spectroscope. Beta particles were subsequently shown to be electrons, and gamma rays to consist of electromagnetic radiation of the same nature as X rays but of considerably greater energy.
A The Nuclear Hypothesis
In 1911 Rutherford proved the existence of a nucleus within the atom by experiments with alpha particles.
At the time of the discovery of radioactivity physicists believed that the atom was the ultimate, indivisible building block of matter. The recognition of alpha and beta particles as discrete units of matter and of radioactivity as a process by means of which atoms are transformed into new kinds of atoms possessing new chemical properties because of the emission of one or the other of these particles brought with it the realization that atoms themselves must have structure and that they are not the ultimate, fundamental particles of nature. In 1911 Rutherford proved the existence of a nucleus within the atom by experiments in which alpha particles were scattered by thin metal foils (see Atom). The nuclear hypothesis has since grown into a refined and fully accepted theory of atomic structure, in terms of which the entire phenomenon of radioactivity can be explained. Briefly, the atom is thought to consist of a dense central nucleus surrounded by a cloud of electrons. The nucleus, in turn, is composed of protons equal in number to the electrons (in an electrically neutral atom), and neutrons. An alpha particle, or doubly charged helium ion, consists of two neutrons and two protons, and hence can be emitted only from the nucleus of an atom. Loss of an alpha particle by a nucleus results in the formation of a new nucleus, lighter than the original by four mass units (the masses of the neutron and of the proton are about one unit each). An atom of the uranium isotope of mass 238, upon emitting an alpha particle, becomes an atom of another element of mass 234. Each of the two protons that form part of the alpha particle emitted from an atom of uranium-238 possesses a unit of positive electric charge. The number of positive charges in the nucleus, balanced by the same number of negative electrons in the orbits outside the nucleus, determines the chemical nature of the atom. Because the charge on the uranium-238 nucleus decreases by two units as a result of alpha emission, the atomic number of the resultant atom is 2 less than that of the original, which was 92. The new atom has an atomic number of 90 and hence is an isotope of the element thorium. See Elements, Chemical; Nuclear Chemistry; Periodic Law.
web center Ä Find the best online information about Radioactivity. Encarta Editors' PicksHow Nuclear Radiation Works more...
Thorium-234 emits beta particles, which are electrons. According to current theory, beta emission is accomplished by the transformation of a neutron into a proton, thus resulting in an increase in nuclear charge (or atomic number) of one unit. The mass of the electron is negligible, thus the isotope that results from thorium-234 decay has mass number 234 but atomic number 91 and is, therefore, a protactinium isotope.
B Gamma Radiation
Gamma emission is usually found in association with alpha and beta emission. Gamma rays possess no charge or mass; thus emission of gamma rays by a nucleus does not result in a change in chemical properties of the nucleus but merely in the loss of a certain amount of radiant energy. The emission of gamma rays is a compensation by the atomic nucleus for the unstable state that follows alpha and beta processes in the nucleus. The primary alpha or beta particle and its consequent gamma ray are emitted almost simultaneously. A few cases are known of pure alpha and beta emission, however, that is, alpha and beta processes unaccompanied by gamma rays; a number of pure gamma-emitting isotopes are also known. Pure gamma emission occurs when an isotope exists in two different forms, called nuclear isomers, having identical atomic numbers and mass numbers, but different in nuclear-energy content. The emission of gamma rays accompanies the transition of the higher-energy isomer to the lower-energy form. An example of isomerism is the isotope protactinium-234, which exists in two distinct energy states with the emission of gamma rays signaling the transition from one to the other.
Alpha, beta, and gamma radiations are all ejected from their parent nuclei at tremendous speeds. Alpha particles are slowed down and stopped as they pass through matter, primarily through interaction with the electrons present in that matter. Furthermore, most of the alpha particles emitted from the same substance are ejected at very nearly the same velocity. Thus nearly all the alpha particles from polonium-210 travel 3.8 cm through air before being completely stopped, and those of polonium-212 travel 8.5 cm under the same conditions. Measurement of distance traveled by alpha particles is used to identify isotopes. Beta particles are ejected at much greater speeds than alpha particles, and thus will penetrate considerably more matter, although the mechanism by means of which they are stopped is essentially similar. Unlike alpha particles, however, beta particles are emitted at many different speeds, and beta emitters must be distinguished from one another through the existence of the characteristic maximum and average speeds of their beta particles. The distribution in the beta-particle energies (speeds) necessitates the hypothesis of the existence of an uncharged, massless particle called the neutrino, and neutrino emission is now thought to accompany all beta decays. Gamma rays have ranges several times greater than those of beta particles and can in some cases pass through several inches of lead. Alpha and beta particles, when passing through matter, cause the formation of many ions; this ionization is particularly easy to observe when the matter is gaseous. Gamma rays are not charged, and hence cannot cause such ionization directly, but when they interact with matter they cause the ejection of electrons from atoms; the atoms minus some of their electrons are thereby ionized (see Radiation Effects, Biological). Beta rays produce t to z of the ionization generated by alpha rays per centimeter of their path in air. Gamma rays produce about t of the ionization of beta rays. The Geiger-Müller counter and other ionization chambers (see Particle Detectors), which are based on these principles, are used to detect the amounts of individual alpha, beta, and gamma rays, and hence the absolute rates of decay of radioactive substances. One unit of radioactivity, the curie, is based on the decay rate of radium-226, which is 37 billion disintegrations per second. The newer and preferred unit for measuring radioactivity in the International System of Units is called the becquerel. It is equal to one disintegration per second.
Modes of radioactive decay, other than the three above mentioned, exist. Some isotopes are capable of emitting positrons, which are identical with electrons but opposite in charge. The positron-emission process is usually classified as a beta decay and is termed beta-plus emission to distinguish it from the more common negative-electron emission. Positron emission is thought to be accomplished through the conversion, in the nucleus, of a proton into a neutron, resulting in a decrease of the atomic number by one unit. Another mode of decay, known as K-electron capture, consists of the capture of an electron by the nucleus, followed by the transformation of a proton to a neutron. The net result is thus also a decrease of the atomic number by one unit. The process is observable only because the removal of the electron from its orbit results in the emission of an X ray. In recent years it has been shown that a number of isotopes, notably uranium-235 and several isotopes of the artificial transuranium elements, are capable of decaying by a spontaneous-fission process, in which the nucleus is split into two fragments. In the mid-1980s a unique decay mode was observed, in which isotopes of radium of masses 222, 223, and 224 emit carbon-14 nuclei rather than decaying in the usual way by emitting alpha radiation.
III HALF-LIFE
The decay of some substances, such as uranium-238 and thorium-232, appears to continue indefinitely without detectable diminution of the decay rate per unit mass of the isotope (specific-decay rate). Other radioactive substances show a marked decrease in specific-decay rate with time. Among these is the isotope thorium-234 (originally called uranium X), which, after isolation from uranium, decays to half its original radioactive intensity within 25 days. Each individual radioactive substance has a characteristic decay period or half-life; because their half-lives are so long that decay is not appreciable within the observation period, the diminution of the specific-decay rate of some isotopes is not observable under present methods. Thorium-232, for example, has a half-life of 14 billion years.
IV RADIOACTIVE DECAY SERIES
The uranium-radium [decay] series continues until a nonradioactive isotope of lead is reached.
When uranium-238 decays by alpha emission, thorium-234 is formed; thorium-234 is a beta emitter and decays to form protactinium-234. Protactinium-234 in turn is a beta emitter, forming a new isotope of uranium, uranium-234. Uranium-234 decays by alpha emission to form thorium-230, which decays in turn by alpha emission to yield the predominant isotope, radium-226. This radioactive decay series, called the uranium-radium series, continues similarly through five more alpha emissions and four more beta emissions until the end product, a nonradioactive (stable) isotope of lead (element 82) of mass 206 is reached. Every element in the periodic table between uranium and lead is represented in this series, and each isotope is distinguishable by its characteristic half-life. The members of the series all share a common characteristic: Their mass numbers can be made exactly divisible by four if the number 2 is subtracted from them, that is, their mass numbers can be expressed by the simple formula 4n + 2, in which n is a whole number. Other natural radioactive series are the thorium series, called the 4n series, because the mass numbers of all its members are exactly divisible by four, and the actinium series, or 4n + 3 series. The parent of the thorium series is the isotope thorium-232, and its final product is the stable isotope lead-208. The actinium series begins with uranium-235 (named actinouranium by early investigators) and ends with lead-207. A fourth series, the 4n + 1 series, all the members of which are artificially radioactive, has in recent years been discovered and thoroughly characterized. Its initial member is an isotope of the synthetic element curium, curium-241. It contains the longest-lived isotope of the element neptunium, and its final product is bismuth-209.
An interesting application of knowledge of radioactive elements is made in determining the age of the earth. One method of determining geologic time is based on the fact that in many uranium and thorium ores, all of which have been decaying since their formation, the alpha particles have been trapped (as helium atoms) in the interior of the rock. By accurately determining the relative amounts of helium, uranium, and thorium in the rock, the length of time during which the decay processes have been going on (the age of the rock) can be calculated. Another method is based on the determination of the ratio of uranium-238 to lead-206 or of thorium-232 to lead-208 in the rocks (that is, the ratios of concentration of the initial and final members of the decay series). These and other methods give values for the age of the earth of between 3 billion and 5 billion years. Similar values are obtained for meteorites that have fallen to the surface of the earth, as well as samples of the moon brought back by Apollo 11 in July 1969, indicating the possibility that the entire solar system could be about the same age as the earth.
V ARTIFICIAL RADIOACTIVITY
sidebar SCIENTIFIC DISCOVERIES The Discovery of Fission German chemist and Nobel laureate Otto Hahn and Austrian-Swedish physicist Lise Meitner are credited with roles in discovering nuclear fission, the process of splitting an atom into two or more smaller parts. By the 1930s, Hahn and Meitner had experimented with radioactive materials for some time. After Meitner left Germany in 1938, Hahn and German chemist Fritz Strassmann made a breakthrough in their experimentation methods that enabled them to collect physical data showing that an atom of uranium would “burst” under certain conditions. They announced their finding in 1939. Shortly thereafter, Meitner and British physicist Otto Robert Frisch published a paper that provided a theoretical explanation for the process, and named it “fission.” This article by Hahn, which appeared in Scientific American in 1958, describes how, through a number of twists and turns in the road, he and his colleagues discovered the fission process in uranium. open sidebar
All the naturally occurring isotopes above bismuth in the periodic table are radioactive and in addition naturally radioactive isotopes of bismuth, thalium, vanadium, indium, neodymium, gadolinium, hafnium, platinum, lead, rhenium, lutetium, rubidium, potassium, hydrogen, carbon, lanthanum, and samarium exist. In 1919 Rutherford carried out the first nuclear reaction when he bombarded ordinary nitrogen gas (nitrogen-14) with alpha particles and found that the nitrogen nuclei captured alpha particles and emitted protons very rapidly, forming a stable isotope of oxygen, oxygen-17. This reaction can be written symbolically as
¨N + ¸He →©O + §Hin which the atomic numbers of the participating nuclei are conventionally written below and to the left of the chemical symbols and their mass numbers above and to the left. In the above reaction the alpha particle is shown as a helium nucleus and the proton as a hydrogen nucleus.
Not until 1933 was it demonstrated that such nuclear reactions could sometimes result in the formation of new radioactive nuclei. The French chemists Irène and Frédéric Joliot-Curie prepared the first artificially radioactive substance in that year when they bombarded aluminum with alpha particles. The aluminum nuclei captured alpha particles and then emitted neutrons with the consequent formation of an isotope of phosphorus, which decayed by positron emission with a short half-life. They also produced an isotope of nitrogen from boron and one of aluminum from magnesium. Since that time a great many nuclear reactions have been discovered, and the nuclei of elements throughout the periodic table have been bombarded with different particles, including alpha particles, protons, neutrons, and deuterons (ions of the hydrogen isotope of mass 2). As a result of this intensive investigation, more than 400 artificial radioactivities are now known. This research has been aided immeasurably by the development of particle accelerators that accelerate the bombarding particles to enormous speeds, thus in many cases increasing the probability of their capture by the target nuclei.
The vigorous investigation of nuclear reactions and the search for new artificial radioactivities, especially in connection with the search for such activities among the heavier elements, was responsible for the discovery of nuclear fission and the subsequent development of the atomic bomb (see Nuclear Energy; Nuclear Weapons). The investigations have also resulted in the discovery of several new elements that do not exist in nature. The development of nuclear reactors has made possible the production on a large scale of radioactive isotopes of nearly all the elements of the periodic table, and the availability of these isotopes is an incalculable aid to chemical research and to biological and medical research (see Isotopic Tracers). Of great importance among the artificially produced radioactive isotopes is an isotope of carbon, carbon-14, which has a half-life of about 5730 ± 40 years. The availability of this substance has made possible the investigation of numerous aspects of life processes, such as the process of photosynthesis, in a more fundamental manner than hitherto considered possible.
Estimates of the ages of objects such as bones and mummies have been made by carbon-14 measurements.
Scientists have recently shown that a very minute but unchanging amount of carbon-14 is present in the atmosphere of the earth and that all living organisms assimilate traces of this isotope during their lifetime. After death this assimilation ceases and the radioactive carbon, constantly decaying, is no longer maintained at a steady concentration. Estimation of the ages of a number of objects, such as bones and mummies, of historical and archaeological interest have been made possible by carbon-14 measurements. See Dating Methods.
further reading These sources provide additional information on Radioactivity.
In neutron-activation analysis, a sample of a substance is made radioactive in a nuclear reactor. A number of impurities that cannot be detected by other means can then be found by detecting the particular types of radioactivity that are associated with radioisotopes of these impurities. Other applications of radioactive isotopes are in medical therapy, industrial radiography, and specific devices such as phosphorescent light sources, static eliminators, thickness gauges, and nuclear batteries
© 1993-2003 Microsoft Corporation. All rights reserved.
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