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View the top otherworldly images from the last year.
Which pictures struck a cosmic chord in 2013? Check out the year's top images from the outer-space beat.
A halo appears around the moon in Kvæfjord, Troms, Norway, on Feb. 19, 2013. Such halos occur when moonlight is refracted by ice crystals in the atmosphere.
•More photos by Steve Nilsen
The Horsehead Nebula takes on an eerie glow in an infrared image from the Hubble Space Telescope. This picture, released on April 21, marked the 23rd anniversary of the famous observatory's launch in 1990 aboard the space shuttle Discovery.
A witch appears to be screaming out into space in this image from NASA's Wide-field Infrared Survey Explorer, released Oct. 31. The infrared portrait shows the Witch Head nebula, named after its resemblance to the profile of a wicked witch. (Can't see the resemblance? Her nose points to the right, halfway up the frame.) Astronomers say the billowy clouds of the nebula are being lit up by massive stars.
Members of the Mars Desert Research Station's Crew 125 EuroMoonMars B mission return after collecting geological samples in the Utah desert on March 2. To simulate the conditions that future explorers will face on Mars, the crew members put on simulated spacesuts every time they venture outside the research station during a mission.
An enlarged portion of this image shows an unfortunate frog flying in the air as NASA's Lunar Atmosphere and Dust Environment Explorer, or LADEE, blasted off from NASA's Wallops Flight Facility in Virginia on Sept. 6. LADEE went into lunar orbit to study the moon's thin atmosphere and surface dust.
•Frog pops up in NASA photo
Saturn is surrounded by planets and moons in a mosaic assembled from images captured by NASA's Cassini probe on July 19. The backlit picture of the ringed planet includes Earth's tiny speck and the even tinier speck representing our moon. But that's not all: A full-resolution image also reveals Mars and Venus, as well as seven of Saturn's moons.
•Saturn probe's big pic finally unveiled
The spinning vortex of Saturn's north polar storm resembles a deep red rose in this color-coded infrared image from NASA's Cassini spacecraft. Measurements have sized the eye at a staggering 1,250 miles across. This image was taken from a distance of 261,000 miles on Nov. 27, 2012, and distributed by NASA on April 29, 2013.
Usually, the European Space Agency sends astronauts to outer space, but these astronauts, in an image released Oct. 4, are in a cave on the island of Sardinia, Italy. Six astronauts from around the world spent six days underground to learn how to work together under extreme conditions.
A close-up of the dying star NGC 6302 nebula is seen in this image released by NASA on June 7. The picture was produced from data acquired by the Hubble Space Telescope's Wide Field Camera 3 in 2009. With an estimated surface temperature of about 250,000 degrees C (450,032 degrees F), the dying central star of this particular planetary nebula has become exceptionally hot, shining brightly in ultraviolet light but hidden from direct view by a dense torus of dust.
Canadian astronaut Chris Hadfield's image is refracted through a floating blob of water aboard the International Space Station. The photo was made available via Twitter on Jan. 27.
The moon rises over the Greek temple of Poseidon as tourists enjoy the sunset at Cape Sounion on June 22. The "supermoon" is so named because it's the year's biggest, brightest full moon.
Three planets - Jupiter (top), Venus (lower left) and Mercury - are revealed after sunset above the round domes of the telescopes at the European Southern Observatory's La Silla Observatory in northern Chile on May 26.
In this composite image released on May 23, visible-light observations by the Hubble Space Telescope are combined with infrared data from the ground-based Large Binocular Telescope in Arizona to assemble a dramatic view of the well-known Ring Nebula. The combined imagery gave astronomers a deeper understanding of the nebula's structure. "The nebula is not like a bagel, but rather, it's like a jelly doughnut, because it's filled with material in the middle," says C. Robert O'Dell of Vanderbilt University.
This self-portrait of NASA's Curiosity rover combines dozens of exposures taken by the rover's Mars Hand Lens Imager on Feb. 3. The rover was positioned at a patch of flat outcrop called "John Klein," the site for the first rock-drilling activities by Curiosity. Because of the process by which the pictures were taken, the rover's robotic arm is not visible in the mosaic.
Civilian passengers in an Airbus A330 Zero-G jet enjoy moments of weightlessness on March 15 during the first zero-gravity airplane flight for paying passengers in France. All of the available slots for 2013 and 2014 were sold out, at a cost of 6,000 euros per person. The airplane ride simulates the microgravity of orbital space missions by going through parabolic flight maneuvers that counter the force of gravity.
Mountain ridges near San Alberto in Mexico look like a reptilian eye in this view from the International Space Station. Canadian astronaut Chris Hadfield uses a different metaphor: "A Dali watch on an alligator wristband." The picture was taken on April 15 and shared via social media on April 25.
Astrophotographer Damian Peach snapped this picture of Comet ISON on Nov. 15. The comet, formally known as C/2012 S1, was discovered a little more than a year ago. Even then, astronomers recognized that it had the potential to become the "comet of the century," owing to the fact that it was due to come well within a million miles (1.6 million kilometers) of the sun.
•Looking for the 'comet of the century'? Watch ISON online
This light-year-long knot of interstellar gas and dust, shown in a picture from the Hubble Space Telescope on Aug. 29, resembles a caterpillar on its way to a feast. But the meat of the story is not just what this cosmic caterpillar eats for lunch, but also what's eating it. Harsh winds from extremely bright stars in the Cygnus OB2 association are blasting ultraviolet radiation at this "wanna-be" star and sculpting the gas and dust into its long shape.
NASA astronaut Chris Cassidy takes part in a spacewalk to replace a leaky pump controller box on the International Space Station's far port truss on May 11. The repair job was successful, enabling the station to make full use of its power-generating system.
Russia's Soyuz TMA-08M spacecraft departs from the International Space Station on Sept. 11, heading toward a landing in a remote area near the town of Zhezkazgan in Kazakhstan. Russian cosmonaut Pavel Vinogradov, NASA astronaut Chris Cassidy and Russia's Alexander Misurkin came back to Earth after five and a half months on the space station.
Snow-covered farmland in Central Asia looks like a complex patchwork when seen from the International Space Station. Canadian astronaut Chris Hadfield calls this picture "a monochromatic 3-D hallucination in the snow." The photo was taken on Feb. 25 and shared by Hadfield on March 14.
Morning clouds cast shadows off the coast of China on Feb. 9, in this view from the International Space Station.
A Project Loon high-altitude balloon sails over Tekapo in southern New Zealand after its launch on June 15. The test was part of Google's plan to send balloons to the edge of space, with the lofty aim of bringing the Internet to the two-thirds of the global population currently without Web access
The trail of a meteor is seen over Chelyabinsk, Russia, on Feb. 15. The meteor streaked across the sky and blew up, releasing as much energy as an atomic bomb and setting off a shock wave. More than 1,600 people were injured, many of them by flying glass from broken windows.
Belgian tourists watch a hybrid solar eclipse from Lake Oloidien near Naivasha in Kenya on Nov. 3, 2013. A rare solar eclipse swept across parts of the U.S., Africa and Europe on with some areas witnessing a total blackout and others experiencing a partial version.
Magnetic loops rise from the sun's surface, as seen in an image captured by NASA's Solar Dynamics Observatory. Such loops lie at the heart of eruptions on the sun known as coronal mass ejections, or CMEs. The image was captured on July 19, 2012, and released to the public on Feb. 20, 2013.
Astrophotographer Randy Halverson captured this shot of a Perseid meteor streak against the backdrop of the Milky Way in Wyoming's Red Desert on Aug. 11. For more of Halverson's work, check out DakotaLapse.com.
This glittering picture shows X-ray emissions from young sunlike stars in the "wing" of the Small Magellanic Cloud, a satellite galaxy associated with the larger Milky Way. The Small Magellanic Cloud lies about 180,000 light-years from Earth. In this April 4 picture, readings from the Chandra X-ray Observatory are shown in purple; visible light seen by the Hubble Space Telescope is in red, green and blue; and infrared readings from the Spitzer Space Telescope are indicated in red.
China's six-wheeled lunar rover Yutu, or "Jade Rabbit," explores the surface of the moon on Dec. 15 in this image taken by the camera on the Chang'e 3 probe after China successfully carried out the world's first soft landing of a space probe on the moon in nearly four decades. Hours later, video footage showed the probe's rover rolling onto the lunar surface. The achievement marked the next stage in an ambitious space program that aims to eventually put a Chinese astronaut on the moon.
This view from the International Space Station shows the sun heading toward the horizon over southwestern Australia on April 2. The space station's solar panels loom in the foreground.