Charlene Sargent, age I6, of Moorhead, Minn., for her question:
WHEN WAS THE FIRST OBSERVATORY BUILT?
An observatory is a building or institution where astronomers study the heavens.
In ancient times, men built observatories to study the positions of the stars, sun, planets and moon. Stonehenge, a monument in Wiltshire, England, is the oldest known structure once used as an observatory. This arrangement of stone slabs was built about 4800 B.C.
By about A.D. 300, Mayan Indian astronomers in Central American observatories had developed an accurate calender based on observations of objects in the sky.
During the il:670s, observatories started to use refracting telescopes. These new telescopes allowed astronomers to determine the positions of objects in the universe more accurately than ever before.
In 11675, King Charles II of England started the Royal Greenwich Observatory in Greenwich. This early observatory provided charts that gave the exact locations of various stars for sailors to follow in navigation.
During the 3800s, many new scientific instruments came into use in observations. With this new equipment, astronomers were able to study the composition of the stars for the first time. Spectrographs were used for the first time in the mid 1800s.
Cameras became one of the chief tools of the observatories by the late iI800s.
In the early 1900s, most of the large optical observatories started to use reflecting telescopes. Astronomers also developed radio telescopes and orbiting astronomical observatories in the mid ,1900s.
Many observatories have taken part in the space exploration program by providing valuable information needed to guide rockets and satellites.
Astronomers can now connect two or more radio telescopes in an observatory to form a radio interferometer. A radio interferometer can produce a clearer image than a single radio telescope.
The United States now has four national observatories: the Cerro Toledo Inter American Observatory in La Serena, Chile; the Kit Peak National Observatory near Tucson, Ariz.; the National Radio Astronomy Observatory in Green Bank, W.Va.; and the National Astronomy and Ionosphere Center, with sites in Ithaca, N.Y., and Arecibo, Puerto Rico.
The world's largest radio telescope, with a reflector 1,000 feet in diameter, is located in the observatory in Arecibo, Puerto Rico.
The world's largest reflecting telescope, with a mirror 236 inches in diameter, is located in Zelenchukskaya, Russia. The largest reflecting telesclope in the United States is located at the Mount Palomar Observatory near San Diego, Calif. It has a mirror 200 inches in diameter.
The world's largest refracting telescope, with a lens 40 inches in diameter, is located at Yerkes Observatory in Williams Bay, Wisc.