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 in November 2009. NASA
Gamma-ray bursts are the universe's biggest explosions, capable of producing so much light that ground-based telescopes easily detect it billions of light-years away, as in this shot from NASA. NASA
NASA's Moon Mineralogy Mapper, an instrument on the Indian Space Research Organization's Chandrayaan-1 mission, took this image of Earth's moon. It is a three-color composite of reflected near-infrared radiation from the sun, and illustrates the extent to which different materials are mapped across the side of the moon that faces Earth. Small amounts of water were detected on the surface of the moon at various locations. ISRO/NASA/JPL-Caltec/Brown Univ./USGS
Astronaut Robert Satcher uses a digital still camera to take a self-portrait during the STS-129 mission's first spacewalk. During the six-hour and 37-minute spacewalk in November 2009, Satcher and astronaut Mike Foreman (not shown) installed a spare S-band antenna structural assembly to the Z1 segment of the station's truss, or backbone. Satcher and Foreman also installed a set of cables for a future space-to-ground antenna on the Destiny laboratory. NASA
On Nov. 3, 1973, the Mariner Venus/Mercury 1973 spacecraft, also known as Mariner 10, was launched from NASA's Kennedy Space Center, becoming the first spacecraft designed to use gravity assist. Three months after launch it flew by Venus, changed speed and trajectory, then crossed Mercury's orbit in March 1974. This photo identifies the spacecraft's science instruments, which were used to study the atmospheric, surface and physical characteristics of Venus and Mercury. This was the sixth in the series of Mariner spacecraft that explored the inner planets beginning in 1962. NASA/JPL
NASA's Ares I-X rocket is seen on Launch Pad 39B at the Kennedy Space Center in Cape Canaveral, Fla., on Oct. 26, 2009. NASA/Bill Ingalls
Arp 274, also known as NGC 5679, is a system of three galaxies that appear to be partially overlapping in the image, although they may be at somewhat different distances. The spiral shapes of two of these galaxies appear mostly intact. The third galaxy (to the far left) is more compact, but shows evidence of star formation. Two of the three galaxies are forming new stars at a high rate. This is evident in the bright blue knots of star formation that are strung along the arms of the galaxy on the right and along the small galaxy on the left. STScI/AURA/NASA
The boosters of the Soyuz rocket that transported Expedition 19 to the space station are shown here as the Soyuz TMA-14 spacecraft and boosters are assembled on March 23, 2009, at the Baikonur Cosmodrome in Kazakhstan. The Soyuz successfully launched on March 26, carrying Expedition 19 Commander Gennady Padalka and Flight Engineer Mike Barratt, as well as a US spaceflight participant. NASA/Bill Ingalls
Backdropped by the blackness of space and the thin line of Earth's atmosphere, space shuttle Atlantis' payload bay and Canadian-built remote manipulator arms are seen in May 2009. NASA
This is an image of a far-off galaxy taken from the Wide Field Planetary Camera 2 (WFPC2) onboard the Hubble Space Telescope. NASA
NASA pilots Jack Nickel (in the jet with tail number 62) and Charles Justiz fly over for a bird's eye view of two shuttles on the launch pad. Shuttle Atlantis is in the foreground and Endeavour can be seen in the distance on the launch pad at NASA's Kennedy Space Center. The two are flying T-38 jet trainer aircraft in April 2009. NASA/Robert Markowitz
Fewer than 7,000 votes separated El Salvador's ruling party candidate and his rival. Both men claimed victory, fueling worries in a country whose democracy is hard-won.
Seth Robbins, Correspondent /
March 10, 2014
Ruling party candidate Salvador Sánchez-Cerén led by the thinnest of margins over his right-wing rival in the second round of presidential elections, raising tensions in this tiny Central American country where democratic institutions have gained a hard-won footing.