Telescope
The principle of the telescope was first developed by a Dutch spectacle-maker, Hans Lippershey (1570-1619). He used his first telescope, made in 1608, for observing grounded objects from a distance, rather than astronomy. His invention was not openly embraced by the scientific community; he was, in fact, unable to patent it.
In 1609, not far away, Italian mathematics professor Galileo developed his own refractor telescope, without seeing even a model of Lippershey's work. His creation had an object glass that bent light rays to a focus near the eye. There a second lens, an eyepiece, magnified the image. His invention grew to be quite popular, as glass was relatively cheap and mirrors of the day were of very poor quality. Galileo's first telescope was small by today's standards and it's object glass was only one inch in diameter.
This simple instrument allowed Galileo to make astonishing discoveries. He saw that the Milky Way comprised thousands of stars, he identified darkened blemishes on the moon's surface as craters, and he also noted changes (phases) of the moon's shape. Galileo's instrument was soon enhanced by that of Johannes Kepler (1571-1630), the German astronomer whose creation increased the field-of-view as well as the he discovered Uranus in 1781.
Even today, reflectors are perhaps the most prominent type of telescope. Some of the largest reflective telescopes are located on Palomar Mountain near San Diego, California and on Mount Pastukhov in Russia. Reflectors are cost-effective, produce little false color, and maintain a high resolution. The mirrors used in larger reflectors, however, often cause distortion due to the weight on the instrument. Newer reflectors are incorporating mirrors of varying shapes (hexagonal glass segments, for example) and are produced using lighter, more durable materials (such as Pyrex). Another approach to eliminate sag is to build several large mirrors, mount them separately on a common base, and link them via computer into one central unit.
The latter part of the nineteenth century saw the resurgence of refracting telescopes. What began as a hobby for American astronomer Alvan Clark ended as a very notable enterprise. For years, Clark had made his own mirrors and lenses. Realizing his were superior to any made in Europe, he set out to manufacture the highest quality lenses possible for sale worldwide. He was successful enough to eventually be given the task of building what was then world's largest refractor: the 36-inch Lick Observatory telescope in California.
After the telescope's completion in 1887, Clark worked with the University of Southern California in developing an even larger telescope--the university was to buy the lenses and the land was to come from private donation. Unfortunately, due to problems in the real estate market, the project was cancelled. Upon hearing of this, George Ellery Hale (inventor of thespectroheliograph used in solar studies) formulated a plan to complete what Clark and the university had begun. Hale worked to secure funding for the project. He struck an agreement with Charles Yerkes, a Chicago railroad millionaire, who fronted over $300,000 for the construction of the world's largest refractor--Yerkes Observatory was built in 1897 near Chicago, Illinois.
It soon became obvious to Hale that because of resolution flaws and inconsistencies in the resulting images, the size was close to the maximum for a refracting telescope. Realizing the need for sharper, more distant images the scientific community turned again to the reflector telescope and a new instrument developed by German optician Bernhard Schmidt--the refractor-reflector telescope. Schmidt invented the first combination refractor-reflector telescope in 1931 for wide-angle astro photography. It had a thin, specially shaped lens at the end of a tube and a regular mirror at the other end; a photographic plate was also included.
The largest Schmidt telescope is located at Palomar Observatory (California). It can photograph an area of the sky more than 300 times as large as that seen by other reflectors; this is key in mapping the skies and closely studying objects at a significant distance. The multiple atmospheric layers have hampered telescope observations from the Earth's surface, absorbing infrared, ultraviolet, and x-ray radiation. Scientists, therefore, have developed other more efficient means for gathering data on our solar system. These instruments include the space telescope and the solar telescope.
In an attempt to raise telescopes above the atmosphere without launching them into space, scientists have flown instruments in airplanes, performing observations at high altitudes. One such example was the Kuiper Airborne Observatory, a C-141 cargo plane fitted with a 450-lb. infrared telescope. The missions generally took place at 41,000 feet, where the telescope could be above 99% of the atmospheric water vapor responsible for absorbing infrared radiation. Commissioned in 1974, the Kuiper discovered the rings of Uranus in 1977, and atmosphere around Pluto in 1988. Plans call for the now-retired Kuiper to be replaced by the Stratosphic Observatory for Infrared Astronomy (SOFIA).
In an extension of the Kuiper Observatory principle, in 1995 scientists flew a trio of ultraviolet telescopes in the space shuttle Endeavor. Known collectively as Astro-2, the telescopes remained aloft for 16 days, capturing image after image of the universe. Because ultraviolet radiation is emitted by hot young stars or very old stars, the Astro-2 images showed a very different picture of the universe, revealing structures within galaxies, and even whole galaxies themselves, not seen in visible-light images.
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