Astronomical observatory

(astronomy) A building designed and equipped for making observations of astronomical phenomena.

A telescope or telescopes, their protective enclosures (if any), support and headquarters buildings, and the staff of astronomers, engineers, technicians, and other support personnel. The telescopes can be optical or infrared (reflecting or refracting) inside a corotating dome, or radio dishes without enclosures.

The on-site support building contains the control room with the computers and control electronics to operate and point the telescope, as well as the data acquisition computers and electronics for detector instruments. It houses laboratories for testing and calibrations, a machine shop for emergency repair and fabrication of parts, and storage for inactive instruments or telescope optics. These areas are often incorporated into a single building along with the telescope and dome. Since telescopes are generally located at remote sites to maximize their usefulness, the administration and support offices are often located in a separate headquarters building miles away in a town or university.

Optical and infrared observatories are the most common types of observatory. They are often located in remote mountains to minimize the effects of contaminating artificial lights and atmospheric blurring. Some countries place their largest telescopes at the best sites in the world such as the 13,800-ft-high (4200-m) volcanic mountain Mauna Kea in Hawaii and La Palma in the Canary Islands.

Optical observatories study planets, stars, nebulae, and galaxies. A large aperture is needed to collect the faint light of these sources. Sizes typically range from 0.5 to 10 m (20–400 in.). The smaller telescopes can use glass lenses, the largest refractor being the University of Chicago 1.0-m (40-in.) Yerkes. For the largest telescopes, engineering and manufacturing constraints dictate the reflecting design. The 9.8-m (386-in.) Keck Telescope is the world's largest reflector. The Very Large Telescope Project seeks to combine the light from four 8.1-m (319-in.) telescopes to effectively have the light-gathering capability of a 16-m (630-in.) telescope.

Most optical observatories can also observe in the near-infrared region. Infrared observatories have been optimized to work farther into the longer (thermal) infrared. Since glass absorbs infrared light, all infrared telescopes are of the reflecting type. Special design techniques must be used, as the telescope itself glows in the infrared.

Radio observatories have become an essential complement to optical observatories. With their longer wavelengths, the radio telescopes can see through cosmic clouds and measure the properties (temperature, pressure, chemical composition, and velocities) of gases which pervade the universe. Since the wavelengths are so long, the telescopes must be large to achieve a high resolution (the ability to discriminate between two nearby sources), and radio dishes are typically tens to hundreds of meters wide.

The longer radio wavelengths allow the use of interferometers, where the signal from several small radio telescopes can be mathematically combined to yield results as if they had been collected from a very large dish. The Very Large Array radio observatory in Socorro, New Mexico, has twenty-seven 25-m (82-ft) antennas arranged in a Y pattern, which can yield the resolution of a single telescope 36 km (22 mi) wide. The Very Long Baseline Array uses ten 25-m (82-ft) antennas spread from Hawaii to the Virgin Islands, allowing the resolution of a telescope dish that distance across.

Crewless balloons have been used to hoist telescopes above the absorbing atmosphere for gamma-ray, x-ray, and ultraviolet observations. Their lower cost (compared to space missions) is offset by the short duration of the observations. The National Aeronautics and Space Administration (NASA) successfully operated the Kuiper Airborne Observatory for 20 years. Space observatories have amply proven their worth despite their initial high cost and limited mission lifetimes. See also Satellite (astronomy).

An astronomical instrument is the working heart of an observatory. The telescope exists solely to collect and funnel light into the instrument. Astronomical instruments range from a simple eyepiece for direct viewing (with different magnifications), to a camera for imaging on film or electronic detectors, to a spectrograph which records the wavelength distribution of light energy (analogous to a rainbow). The charge-coupled device (CCD) has now virtually supplanted the photographic plate. For radio telescopes the instrument is an amplifier that isolates and boosts the weak celestial electric signal. See also Astronomical spectroscopy; Camera; Charge-coupled devices; Spectrograph.

Besides observing light (electromagnetic radiation), astronomers are mapping the universe via neutrinos, particles that can transverse matter with a minimum of interaction. Gravitational wave observatories attempt to detect ripples (gravitational waves or gravitons) in the fabric of space-time itself. See also Neutrino astronomy.