SPACE.com asked scientists, photographers, authors and space leaders for their favorite space photos. This 1995 picture from the Hubble Space Telescope, called the "Hubble Deep Field," was a popular choice. It reveals thousands of distant galaxies by combining light collected over many hours. For the rest of our experts' favorite photos, click through the gallery.
Science-fiction author Ben Bova, author of the “Grand Tour” series and others, writes: "My favorite space image is the picture taken by one of the Voyager spacecraft looking back at 'the pale blue dot' of Earth." The narrow-angle color image of the Earth is a part of the first "portrait" of the solar system taken by Voyager 1. The spacecraft acquired a total of 60 frames for a mosaic of the solar system from a distance of more than 4 billion miles from Earth and about 32 degrees above the ecliptic. Image released Feb. 14, 1990.
Jeff Hall, director of the Lowell Observatory in Flagstaff, Ariz., chose this image of a crescent Neptune and Triton captured by the Voyager 2 spacecraft. Hall used this image in a presentation accompanied by the music of Gustav Holst’s The Planets. Hall noted that when Holst wrote the music about 100 years ago, Pluto had not yet been discovered, and a scientist named Vesto M. Slipher was making measurements that laid the groundwork for the later discovery that there were galaxies beyond our own Milky Way.
“With this image, Voyager captured the extent of our knowledge from exactly 100 years ago, and from a vantage point I’m sure both Holst and Slipher would have been thrilled to see,” Hall said. “We would do well to consider it today and to wonder what the analogous image of 2112 will be!”
"Earthrise," the first picture taken of planet Earth by people orbiting the moon, was another popular choice for favorite space photo. This shot was captured by Apollo 8 astronaut Bill Anders on December 24, 1968, as his spacecraft became the first to fly around the moon.
"It was iconic for the environmental movement," said astronomer Jill Tarter, co-founder of the SETI (Search for Extraterrestrial Intelligence) Institute. "It allowed us to see ourselves as Earthlings living on a single, fragile, beautiful planet. This perspective is even more important today, many of the challenges we face require long-term thinking and global cooperation; they do not respect national boundaries."
This photo, called "Earth From Mars," was taken by NASA's Mars Exploration Rover Spirit on March 8, 2004. It was the first image of Earth seen from the surface of a planet beyond the moon.
It was chosen by Nobel Prize-winning physicist Frank Wilczek of MIT, who said it is "actually far from beautiful," but that he finds it "meaningful and deeply moving."
This image of the crescent planet Neptune and its crescent moon Triton, taken by NASA's Voyager 2 spacecraft in 1989, is the favorite of University of California, Santa Cruz astronomer Greg Laughlin.
"There's no false color, no artifice, no agenda," Laughlin said. "This photograph is calming, mysterious and aesthetically perfect."
This photo shows helmets and spacesuits covered in lunar dust after the last manned moonwalk, from the 1972 Apollo 17 mission. "It symbolizes NASA at its best, and our exploration aspirations for the future," said Southwest Research Institute planetary scientist Alan Stern.
This photo was among the first images taken by the Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory satellite.
"When we first started getting data, after years of work on building the SDO instruments and spacecraft, launching SDO, and early ops, we took our first images and this is what we saw with AIA, [SDO's Atmospheric Imaging Assembly]," said SDO deputy project scientist Phillip Chamberlin. "Absolutely amazing."
This photo of the Allen Telescope Array was taken by SETI astronomer Seth Shostak, who picked it as his favorite shot. The SETI (Search for Extraterrestrial Intelligence) Institute uses this array of radio dishes in Northern California to search for signals from a civilization beyond the solar system. Perhaps one day these telescopes will answer the question, "Are we alone?"
In this photo by NASA's Cassini orbiter around Saturn, the planet Earth is visible as the small bright dot. University of California, Berkeley astronomer Geoff Marcy picked this September 2006 photo as one of his favorites.
Geoff Marcy also chose this photo of water geysers spouting from Saturn's moon Enceladus, taken by Cassini in October 2007.
"This is the best destination to search for life," Marcy wrote. Astronomers think the geyers could indicate Enceladus harbors an ocean of water buried underneath its surface, which might support microbial life.
NASA astronaut Leroy Chiao picked this photo of the moon he took from his vantage point on the International Space Station, about 230 miles (370 km) over Earth.
Former astronaut Leroy Chiao also nominated this photo of Lake Nassar in Egypt, which he took while orbiting Earth, "right as the sun perfectly reflected off of the surface of the water into the camera lens," he said.
Taft Armandroff, director of the W. M. Keck Observatory in Hawaii, sent his favorite space photo. It shows the twin laser beacons of the two Keck 10-meter telescopes on Mauna Kea and their laser adaptive optics systems studying the supermassive black hole at the galactic center.
Australian National University astrophysicist Brian Schmidt sent in his favorite space photo, Supernova SN 1994D, which he called "the poster child of a type Ia supernovae." Dr. Schmidt won the 2011 Nobel Physics prize for his studies of distant supernovas that helped reveal the existence of dark energy.
Astrophotographer Jerry Lodriguss selected this photo of Saturn taken by the Cassini spacecraft in 2006 as his favorite space photo.
Roger Launius, senior curator of space history at the Smithsonian's National Air and Space Museum, writes: "This image of Harrison Schmitt with the lunar rover makes clear one reason Apollo was never followed with additional moon landing efforts. Humanity found nothing there of value that they wished to exploit, as had happened repeatedly in previous terrestrial explorations. Schmitt and artifacts from Earth are swallowed up in the vast expanse of nothingness that was on the lunar surface. Buzz Aldrin called it 'magnificent desolation.' He was right."
Adam Block, astrophotographer and astronomy educator with the University of Arizona's Mt. Lemmon SkyCenter, selected his own image of nebula SH2-239 as his favorite. He writes: "[I] suspect you will not find … a higher resolution (full) color image of this particular nebula. The important idea to consider is that this object is certainly not unknown. This field represents the earliest stages of stellar evolution — the birth place of stars, and it is studied intensively by astronomers. And yet, few color images exist. The reason is because when an astronomer studies an object like this the data that they take is usually not amenable to creating a pretty picture. This is because the astronomer is interested in making a quantifiable measurement in order to understand astrophysical processes of the object of interest. On the other hand, the data (picture) I take is not very good for making these measurements ... but it is nice to show a full color picture of the field, and tell the overall story of this bit of space."
John Grotzinger of Caltech, chief scientist for NASA's Mars rover Curiosity, selected this image of Mars as his favorite, naturally. He writes: "I love this image because its so evocative of Earth, at least on the surface. These foothills of Mount Sharp are the eventual destination for Curiosity, where she will read these layers — like pages in a book — and seek clues regarding the early environmental history of Mars."
Mario Livio, astrophysicist at the Hubble Space Telescope Science Institute, picks the Hubble Ultra Deep Field image as his favorite "because it represents an 'executive summary' of the history of the universe!"
Science-fiction author Jack McDevitt sent in this photo for his submission. He writes: "I don’t really have a favorite astronomical photo, because I see pictures pretty much on a daily basis that blow me away. But this one of NGC 2841, taken by Hubble, is as spectacular as any. This one, more than most galactic photos, provides a sense of immensity, makes me think how someone standing out on the fringe would need 25,000 years, more or less, before he could see a light beam coming out from the center. It almost seems possible."
Elon Musk, founder of private spaceflight company SpaceX, sent in this photo. He writes: "[M]y favorite pic is a relatively personal one. It is the first frame from the video downlink just as Falcon 1 reached orbit. It was the fourth flight of Falcon 1 and our last chance to make orbit. If we hadn't, then SpaceX wouldn't be around."