Optical telescopes use such devices as lenses and mirrors to form magnified images of distant objects. Most radio telescopes use large antennas to capture radio waves from space. Observatories also have such instruments as cameras and electronic sensors to record information gathered by optical and radio telescopes. In most cases, computers guide the telescopes and analyze the data they collect. Astronomers build observatories in places that have good observing conditions, free of such difficulties as those caused by violent atmospheric disturbances, polluted air, and bright lights.
Most optical observatories stand on high mountains, where the sky is almost always clear.
Many radio observatories are in valleys, where the mountains protect them from radio interference from cities and other highly populated areas. Most observatories are operated by universities and are used by teachers and advanced students of astronomy. They are extremely expensive to build and operate, and so national governments or wealthy individuals support many of them. Some important observatories Optical observatories. The telescope in an optical observatory stands under a large dome that has shutters.