The ground-based image of Comet 17P/Holmes was taken November 1, 2007, by astrophotographer Alan Dyer. The observations were made in southern Alberta, Canada. NASA/ESA/A. Dyer
Astronaut Steven Smith took this picture of fellow crew member Mark Lee during Hubble's second servicing mission in 1997. Lee is preparing to document the day's activities with a shuttle camera. Engineers rely on astronauts' photos to design and build new hardware for Hubble, and other astronauts use them for training. In addition to the hand-held cameras, the shuttle has cameras mounted to it in various locations to capture other footage. NASA
The Space Shuttle Discovery drops out of the darkness onto runway 33 at the Shuttle Landing Facility after traveling more than 3,267,000 miles on a successful eight-day mission to service the Hubble Space Telescope. Astronauts Curtis L. Brown Jr., Commander; Scott J. Kelly, Pilot; and Steven L. Smith, C. Michael Foale (Ph.D.), John M. Grunsfeld (Ph.D.), Claude Nicollier of Switzerland and Jean-François Clervoy of France, all Mission Specialists, spent the Christmas holiday in space in order to accomplish their mission before the end of 1999. NASA
This undated close-up of the Helix Nebula was taken by the Hubble Space Telescope. NASA/NOAO/ESA/Hubble Helix Nebula Team/M. Meixner/T.A. Rector
The Space Shuttle Discovery on its Mobile Launch Platform slowly moves through the high bay doors of the Vehicle Assembly Building en route to Launch Pad 39A, where Discovery is scheduled to lift off on the STS-82 mission on Feb. 11, 1997. NASA Kennedy Space Center
This is an artist's impression of our home galaxy, the Milky Way. Our solar system is one of billions in the galaxy. And the galaxy is one of billions in the universe. NASA
Astronomers are using NASA's Hubble Space Telescope to dissect one of the largest structures in the universe as part of a quest to understand the violent lives of galaxies. Hubble is providing indirect evidence of unseen dark matter tugging on galaxies in the crowded, rough-and-tumble environment of a massive supercluster of hundreds of galaxies. The image, taken by NASA's Hubble Space Telescope, shows the supercluster. NASA
Control panel below the test section of the 8-Foot High Speed Tunnel (8-Foot HST). Authorized July 17, 1933, construction of the eight-Foot High Speed Tunnel was paid for with funds from the Federal Public Works Administration. Manly Hood and Russell Robinson designed the unusual facility which could produce a 500 mph wind stream across an 8-Foot test section. Operating personnel located inside the igloo-like structure were subjected to pressures equivalent to 10,000-foot altitude and had to wear oxygen masks and enter through airlocks. NASA Langley Research Center
The Eastman-Kodak mirror assembly is being tested for the James Webb Space Telescope project at the X-Ray Calibration Facility at Marshall Space Flight Center. In this photo, a Marshall employee is inspecting one of many segments of the mirror assembly for flaws. NASA
This undated image is a face-on, false-light image of the dust disk around star HD 141569. Credit: NASA, M. Clampin (STScI), H. Ford (JHU), G. Illingworth(UCO/Lick), J. Krist (STScI), D. Ardila (JHU), D. Golimowski (JHU) the ACS Science Team and ESA
At least 60,000 mostly Kurdish refugees have entered Turkey since Thursday after Islamic State militants surrounded a Kurdish stronghold in northern Syria. Some are calling for US airstrikes to stop the group's advance.
ByDominique Soguel, Correspondent
Tens of thousands of Syrians have crossed into Turkey in recent days, fleeing an Islamic State offensive that has opened up another front in Syria's civil war as the US weighs a bombing campaign there.