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Exploring The Planets Discovery |
The Age of The Telescope
Until the development of the telescope in the early 17th Century, all astronomical observations were made with the naked eye. By using measuring instruments, astronomers recorded the positions of the planets against the background of stars.
When Galileo Galilei turned his telescope to the sky in 1609, planetary astronomy became a new and different science. No longer would astronomers be concerned only with the motions of planets; surfaces of other worlds could now be studied as well.
Development of The Telescope
17th Century Telescopes 
Telescopes had been in use for many years before it was known precisely how they worked. The first theory of the telescope was written by the noted astronomer Johannes Kepler in his book "Dioptrice" published in 1610.
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Machina Coelestis, 1673Hevelius' Longest Telescope
To correct for distortions of lenses, telescopes became longer and longer. For example, the astronomer Hevelius' telescope was approximately 13 meters (43 feet) long. Telescopes longer than 30 meters (100 feet) were not uncommon. Many people were necessary to aid the observer.
The Reflecting Telescope
Sir Isaac Newton designed a reflecting telescope to overcome the chromatic distortions produced by lenses. In his telescope, light was focused by a concave mirror rather than by lenses. The telescope did not have to be a long and unwieldy instrument.
Ancient Times &
The Greeks || The Renaissance || Age
of The Telescope || Galileo
Discovering Planets || Planetary
Satellites
©2002 National Air and Space Museum
