Astronomy Picture of the Day Index - Space Technology: Earth Observatories

APOD: 1997 December 27 - Keck: The Largest Optical Telescopes
Explanation: In buildings eight stories tall rest mirrors ten meters across that are slowly allowing humanity to map the universe. Alone, each is the world's largest optical telescope: Keck. Together, the twin Keck telescopes have the resolving power of a single telescope 90-meter in diameter, able to discern sources just milliarcseconds apart. Since opening in 1992, the real power of Keck I (left) has been in its enormous light- gathering ability - allowing astronomers to study faint and distant objects in our Galaxy and the universe. Keck II, completed last year, and its twin are located on the dormant volcano Mauna Kea, Hawaii, USA. In the distance is Maui's volcano Haleakala. One reason Keck was built was because of the difficulty for astronomers to get funding for a smaller telescope.

APOD: 1999 June 23 - The Sudbury Neutrino Detector
Explanation: Two thousand meters below the ground, a giant sphere has begun to detect nearly invisible particles. These particles, neutrinos, are extremely abundant in the universe but usually go right through just about everything. By stocking this 12-meter sphere with an unusual type of heavy water and surrounding it with light detectors, astrophysicists hope to catch the occasional collision. Since the Sudbury Neutrino Observatory (SNO) is sensitive to all types of neutrinos, future results might hold clues to how much neutrinos change types on the fly, how our own Sun emits neutrinos, and even how important neutrinos are to the composition of the entire universe.

APOD: 1999 June 20 - A Very Large Array of Radio Telescopes
Explanation: Pictured above is one of the world's premiere radio astronomical observatories: The Very Large Array (VLA). Each antenna dish is as big as a house (25 meters across) and mounted on railroad tracks. The VLA consists of 27 dishes - together capable of spanning the size of a city (35 kilometers). The VLA is the most sensitive radio telescope ever, and, through interferometry, can resolve a golf ball-sized radio source 150 kilometers away (0.04 arcsec). The VLA is continually making new discoveries, including determining the composition of galaxies, passing comets, quasars, HII regions, and clusters of galaxies. The VLA is also used to receive the weak radio signals broadcast from interplanetary spacecraft. The VLA is located in New Mexico, USA. A significant upgrade of VLA's capabilities is planned.