Ground-based observatories

For optical telescopes, most ground-based observatories are located far from major centers of population in order to avoid the effects of light pollution. The ideal locations for modern observatories are sites that have dark skies, a large percentage of clear nights per year, dry air, and are at high elevations. At high elevations, the Earth's atmosphere is thinner thereby minimizing the effects of atmospheric turbulence and resulting in better astronomical "seeing". Sites that meet the above criteria for modern observatories include the southwestern United States, Hawaii, the Andes Mountains region, Australia and the mountainous Sierra Negra in Mexico. Major optical observatories include Mauna Kea, HI, USA, Roque de los Muchachos Observatory in Spain, Paranal Observatory in Chile and Kitt Peak observatory in the USA.

The largest observatory in the world is the Large Millimeter Telescope located in the high mountains of the state of Puebla in Mexico.

Radio observatories

Beginning in 1930s, radio telescopes have been built for use in the field of radio astronomy to see space very close up. Such an instrument, or a collection of them, with outbuildings for such things as control centres, data reduction centers, and maintenance are called radio observatories. Radio observatories are similarly located far from major centers of population in order to avoid electromagnetic interference (EMI) from radio, TV, radar, and other EMI emitting devices. But unlike optical observatories, radio observatories will be placed in valleys to further shield them from EMI. Some of the major radio observatories are at Socorro, in New Mexico, USA, Jodrell Bank in the UK, Arecibo, Puerto Rico, Parkes at New South Wales, Australia and Chajnantor in Chile.

Oldest astronomical observatories

The oldest proto-observatories, in the sense of a private observation post, include:

• Chankillo, Peru
• El Caracol, Mexico
• Abu Simbel, Egypt
• Stonehenge, Great Britain
• Kokino, Republic of Macedonia
• Goseck circle, Germany
• Ujjain, India
• Arkaim, Russia
• Cheomseongdae, South Korea
• Angkor Wat, Cambodia

The oldest true observatories, in the sense of a specialized research institute,Peter Barrett (2004), Science and Theology Since Copernicus: The Search for Understanding, p. 18, Continuum International Publishing Group, ISBN 056708969X , in include: