A quarter moon is visible in this oblique view of Earth's horizon and airglow, recorded with a digital still camera on the final mission of the Space Shuttle Columbia. Columbia's crew was killed on Feb. 1, 2003 when the shuttle broke up on re-entry into Earth's atmosphere. NASA
Red and green colors predominate in this view of the Aurora Australis photographed from the Space Shuttle in May 1991 at the peak of the last geomagnetic maximum. The payload bay and tail of the Shuttle can be seen on the right hand side of the picture. NASA
Four hundred bridges cross the labyrinth of canals that form the 120 islands of Venice, situated in a saltwater lagoon between the mouths of the Po and Piave rivers in northeast Italy. All traffic in the city moves by boat. Venice is connected to the mainland, 2.5 miles away, by ferries as well as a causeway for road and rail traffic. NASA/GSFC/METI/ERSDA C/JAROS, and U.S./Japan ASTER Science Team
The Channel Tunnel is a 30 mile-long rail tunnel beneath the English Channel, here seen from space. It connects Dover, Kent in England with Calais, northern France. The undersea section of the tunnel is unsurpassed in length in the world. A proposal for a Channel tunnel was first put forward by a French engineer in 1802. NASA/GSFC/METI/ERSDA C/JAROS, and U.S./Japan ASTER Science Team
This image from the ASTER instrument on NASA's Terra satellite covers an area of 34 by 25 miles over the southwest part of the Malaspina Glacier and Icy Bay in Alaska. The composite of infrared and visible bands results in the snow and ice appearing light blue, dense vegetation is yellow-orange and green, and less vegetated, gravelly areas are in orange. NASA/GSFC/METI/ERSDA C/JAROS, and U.S./Japan ASTER Science Team
During its flight, the Galileo spacecraft returned images of the Earth and Moon. Separate images of the Earth and Moon were combined to generate this view. The Galileo spacecraft took the images in 1992 on its way to explore the Jupiter system in 1995-97. NASA
The shadow of the moon falls on Earth as seen from the International Space Station, 230 miles above the planet, during a total solar eclipse. This digital photo was taken by the Expedition 12 crew, who are wrapping up a six-month mission on the ISS. Visible near the shadow are portions of Cyprus in the Mediterranean Sea and the coast of Turkey. NASA
Small cumulus clouds in this natural-color view from the Multi-angle Imaging SpectroRadiometer have formed a distinctive series of quasi-circular arcs. Clues regarding the formation of these arcs can be found by noting that larger clouds exist in the interior of each arc. The interior clouds are thicker and likely to be more convectively active than the other clouds, causing much of the air near the centers of the arcs to rise. NASA/GSFC/LaRC/JPL, MISR Team
Iceberg B-15A was the largest iceberg in the world (measuring about 11,000 square kilometers) when it broke away from Western Antarctica's Ross Ice Shelf in March 2000. It held that distinction for over three years until splitting into two pieces in early October, 2003. The Multi-angle Imaging SpectroRadiometer (MISR) acquired these views of the new iceberg B-15J (resting against Ross Island) and B-15A (now free to drift into the Southern Ocean). NASA/GSFC/LaRC/JPL, MISR Team
This view of the rising Earth greeted the Apollo 8 astronauts as they came from behind the Moon after the lunar orbit insertion burn. The unnamed surface features in the foreground are near the eastern limb of the Moon as viewed from Earth. On the Earth, 240,000 miles away, the sunset terminator bisects Africa. NASA
This image shows the Arctic sea ice on September 21, 2005, the date at which Earth's sea ice was at its minimum extent in the northern hemisphere. The color of the sea ice is derived from the AMSR-E 89 GHz brightness temperature, while the extent of the sea ice was determined by the AMSR-E sea ice concentration. Over the continents, the terrain shows the average landcover for September, 2004. NASA/Goddard Space Flight Center Scientific Visualization Studio The Blue Marble data is courtesy of Reto Stockli (NASA/GSFC).
The thin line of Earth's atmosphere and the setting sun are featured in this image photographed by the crew of the International Space Station while the space shuttle Atlantis on the STS-129 mission was docked with the station. NASA
From his vantage point high above the earth in the International Space Station, Astronaut Ed Lu captured this broad view of Hurricane Isabel. The image was taken with a 50mm lens on a digital camera. Mike Trenchard/Earth Sciences & Image Analysis Laboratory/Johnson Space Center/NASA
Apollo 9 Command/Service Modules (CSM) nicknamed "Gumdrop" and Lunar Module (LM), nicknamed "Spider" are shown docked together as Command Module pilot David R. Scott stands in the open hatch. Lunar Module pilot Russell L. Schweickart took this photograph of Scott during his EVA as Schweickart stood on the porch outside the Lunar Module. Apollo 9 was an Earth orbital mission designed to test docking procedures between the CSM and LM as well as test fly the Lunar Module in the relatively safe confines of Earth's orbit. NASA
The morning sun reflects on the Gulf of Mexico and the Atlantic Ocean as seen from the Apollo 7 spacecraft during its 134th orbit of the Earth on Oct. 20, 1968. NASA
This composite image, which has become a popular poster, shows a global view of Earth at night, compiled from over 400 satellite images. NASA researchers have used these images of nighttime lights to study weather around urban areas. NASA
Ancient lava flows dating back 2,000 to 15,000 years are shown in light green and red on the left side of this space radar image of the Craters of the Moon National Monument area in Idaho. The volcanic cones that produced these lava flows are the dark points shown within the light green area. NASA/JPL-Caltech
Ames Earth Resources project U-2 aircraft shot this oblique image off the coast of California in 1972. The Golden Gate is in the foreground. As the image looks out across California, the blue spot at the top enter is Lake Tahoe in the Sierra Nevada. NASA Ames Research Center
Backdropped by a blue and white Earth and the blackness of space, Space Shuttle Discovery's docking mechanism (top foreground), payload bay, Remote Manipulator System Orbiter Boom Sensor System, vertical stabilizer, and orbital maneuvering system pods are featured in this image photographed by a STS-119 crewmember in March 2009. NASA
The Hubble Space Telescope hovers at the boundary of Earth and space in this picture, taken after Hubble's second servicing mission in 1997. Hubble drifts 353 miles above the Earth's surface, where it can avoid the atmosphere and clearly see objects in space. NASA
During the first 500 million years after the formation of the Earth, meteors pummeled rained down from the sky, transforming the surface into molten rock. Yet the planet may have been more hospitable than previously thought.
Asteroids and comets that repeatedly smashed into the early Earth covered the planet's surface with molten rock during its earliest days, but still may have left oases of water that could have supported the evolution of life, scientists say.