Molly Hagen, age 14, of Butte, Mont., for her question:
WHO BUILT THE FIRST OBSERVATORY?
An observatory is a place where astronomers study the sun, planets, stars and other objects in the universe. The first observatory was actually built in ancient times because very early man started to study the position of objects in the sky. We don't know who built it.
Stonehenge, a monument in Wiltshire, England, is the oldest known structure once used as an observatory. This arrangement of stone slabs was built about 1800 B.C.
By about A.D. 300, Maya Indian astronomers in Central Amercian had developed an accurate calendar based on observations of objects in the heavens.
During the 1670s, observatories started to use refracting telescopes. These telescopes enabled astronomers to determine the positions of objects in the universe more accurately than ever before.
In 1675, Ring Charles II of England founded the Royal Greenwich Observatory in Greenwich. This observatory provided charts that gave the exact locations of various stars for sailors to follow in navigation.
Many new scientific instruments came into use in observatories during the 1800s. With these instruments, astronomers were able to study the composition of the stars for the first time. Cameras became one of the chief tools of the observatories by the late 1800s.
There are two chief kinds of observatories: the optical observatory, where optical telescopes are used to study light, and the radio observatory, where radio telescopes are used to study radio waves.
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 run by universities and are operated by teachers and advanced students.
Observatories use two principal kinds of optical telescopes: reflecting telescopes and refracting telescopes. Reflecting telescopes use a curved mirror or a set of such mirrors to focus light, and refracting telescopes use a system of lenses.
Most optical observatories use reflecting telescopes which can be made larger than refracting telescopes. The Hale telescope at the Palomar Observatory, near San Diego, Calif., ranks as one of the world's largest reflecting telescopes. Its mirror measures 200 inches in diameter.
Refracting telescopes need thick lenses for high magnification. The refracting telescope at the Yerkes Observatory in Williams Bay, Wis., is the world's largest. Its lens measures 40 inches in diameter.
Some scientists work in solar observatories. This is a type of optical observatory where the scientists study the sun. Such observatories must make special provisions to reduce the effects of the sun's heat.
The radio telescope is made up of a large bowl shaped reflector that collects radio waves.