The interior lights are on in this dusky view of Gemini North, as it prepared for nighttime observation. Two large vent gates and the dome slit are open to help equalize air temperatures inside and outside the dome.
Credit: Robert Scott Fisher

The secondary mirror of Gemini North. The silver-coated mirror is 1.05 meters (41 inches) in diameter. The mirror and related electronics weigh a total of ~750 pounds and are supported by 8 black vanes, referred to as “the spider.”
Credit: Robert Scott Fisher

Sunset portrait of Gemini South, located on the summit of Cerro Pachon in central Chile. Here, Dr. Rachel Mason assesses sky conditions before a night of observing.
Credit: Robert Scott Fisher

Tony Matulonis stands on the catwalk of Gemini North while he prepares the telescope for observing. The Gemini telescopes are roughly 75-feet tall and weigh approximately 350 tons.
Credit: Robert Scott Fisher

View of the Andes Mountains from Gemini South. The constellation Orion is visible just above the snowy peaks, in an “upside down” orientation for people who live in the Northern Hemisphere.
Credit: Robert Scott Fisher

Aerial view of Cerro Tololo Inter-American Observatory in Chile, taken in the late 1970s.
Credit: NOAO/AURA/NSF

As the sun sets, the telescope domes at Cerro Tololo Inter-American Observatory in Chile open their shutters in preparation for a night of observing.
Credit: T. Abbott and NOAO/AURA/NSF

This 1993 aerial photograph of the Kitt Peak mountain, some 50 miles west-southwest of Tucson, Ariz., shows the current configuration of the large collection of telescopes maintained and operated by the National Optical Astronomy Observatories (NOAO).  
Credit: NOAO/AURA/NSF

A twilight view of the McMath-Pierce Solar Telescope (with the moon shining in the background) on Kitt Peak, the largest solar telescope in the world.  
Credit: Bill Livingston/NSO/AURA/NSF

The Heliostat of the McMath Pierce Solar Telescope on Kitt Peak at sunset. 
Credit: NSO/AURA/NSF

Sunlight floods through the dome aperture of the Evans Solar Facility at NSF’s National Solar Observatory (NSO) in Sunspot, N.M.  Its instrument scans the corona to produce maps used in predicting upcoming solar activity.  
Credit: Dave Dooling, NSO/AURA/NSF

The Green Bank Telescope (GBT) is the world's largest, fully steerable radio telescope. It is located in Green Bank, W.Va., in a quiet, radio-free zone. 
Credit: NRAO/AUI

The Green Bank Telescope (GBT) is the world's largest, fully steerable radio telescope. It is located in Green Bank, W.Va., in a quiet, radio-free zone.
Credit: NRAO/AUI

An artist's conception of the antennas for the Atacama Large Millimeter Array (ALMA).
Credit: NRAO/AUI and ALMA/ESO/NRAO/NAOJ

An artist's conception of the Atacama Large Millimeter Array (ALMA) in compact configuration. When construction is finished in 2011, ALMA will be the world's largest and most powerful radio telescope, operating at millimeter and sub-millimeter wavelengths.
Credit: NRAO/AUI and ESO

The Very Large Array (VLA), one of the world's premier astronomical radio observatories, consists of 27 radio antennas in a Y-shaped configuration on the Plains of San Agustin, 50 miles west of Socorro, N.M.
Credit: NRAO/AUI

This shell of hot gas is the remains of a star that exploded around 30,000 years ago, probably the remnant of a core-collapsed supernova, which occurs when a star runs out of fuel for nuclear fusion, collapses under its own weight, and then rebounds, producing a shock wave. The shock front is shown in blue-green radio waves, visible from the Galactic Plane Survey (captured by the Very Large Array radio telescope).  Infrared data from the MSX satellite is shown in red.
Credit: NRAO/AUI

Taken at Kitt Peak using  NSF's 0.9-meter telescope and the NOAO Mosaic CCD camera, this is an image of the Andromeda galaxy, located in the constellation of Andromeda, the Princess.  This true-color image was created by combining images taken in seven filters: U (violet), B (blue), V (green), R (orange), I (red), Hydrogen-Alpha (red) and Oxygen [OIII] (green).
Credit: T.A. Rector and B.A.Wolpa/NOAO/AURA/NSF

A wide-field image of Pickering's Triangle taken with NSF’s Mayall 4-meter telescope at Kitt Peak National Observatory.  Pickering's Triangle is part of the Cygnus Loop supernova remnant, which includes the famous Veil Nebula, located about 1,500 light-years from Earth, in the constellation Cygnus, the Swan.
Credit: T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF

The Crab Nebula (left), located in the constellation of Taurus, is the remnant of a supernova in 1054 AD, observed as a "guest star" by ancient Chinese astronomers. The Crab Nebula (M1) (right) is the remnant of the earliest known supernova explosion, recorded by Chinese astronomers in AD 1054. A novel technique, Homogeneous Mosaicing, developed by radio astronomers during NRAO’s design of the Atacama Large Millimeter Array, enabled this more accurate radio image.
Credit: NRAO/AUI and M. Bietenholz (left); NRAO/AUI (right)

Arecibo Observatory in Puerto Rico simultaneously observes the same targets, simulating a telescope more than 6,800 miles in diameter. May of 2008 marked a live demonstration of their first four-continent, real-time, electronic Very Long Baseline Interferometry (e-VLBI) observations.
Credit: NAIC - Arecibo Observatory, a facility of the NSF