Since the Dutch optician Hans Lippershey first peered through the one he invented in 1608, the telescope has been an important tool in studying "really far out" things. In the past 500 years, there have been great advances in astronomy telescopes, but most have come in the last two centuries.
The first practical telescope was a refracting device, using a long tube with lenses at each end. Galileo developed his own telescope, but his could only magnify objects by three diameters. This might be useful in spying on fellow villagers but was of only limited use in astronomical observations. His later refractor magnified objects by more than 30 times, which enabled him to identify the rings around the planet Saturn and some of the moons of Jupiter. The concept of astronomy telescopes had thus become reality. The 62-foot telescope at the Yerkes Observatory in Wisconsin was built in 1897, and remains today as the largest practical refractor in the world.
Hampering the capability of early telescopes was what is known as chromatic aberration, which is related to the failure of different color light rays to focus simultaneously. One way around this was to increase the focusing length, or focal length, of the telescope. Unfortunately the size of these devices made them impractical. Some exceptionally long refractors did not even use a tube. Instead, the outer lens would be placed atop a tree or some tall structure, using a swiveling ball joint. These too were impractical and difficult to use. A technical advancement that significantly reduced color aberration was the achromatic lens. This not only helped "clear the view" of astronomers but allowed for the development of telescopes that were smaller and more practical. The introduction of the micrometer for concise measuring also made possible the construction of precision telescopes.
The development of the reflecting telescope by British astronomer and mathematician Issac Newton was also an important step in the field of astronomy. A reflector uses a mirror system to "bounce" the light within the telescope, which allows the entire unit to be more powerful and more compact. The largest conventional reflector today is the Gran Telescopio Canarias, whose mirror has a diameter of approximately 34 feet. Several technical developments made possible larger and more precise reflecting telescopes. These included the bowl-shaped paraboloidal mirror and the process of silvering, which involves coating the glass components of a telescope with a reflective material.
Different types of telescopes developed over time have put to use newer technologies. The Ritchey-Chretien reflector used two mirrors with hyperbolic curving, which eliminated aberrations associated with the shape of glass components. The Off-Axis design and the Schietspiegler reflector were designed to reduce obstructions created by inside components and thus to prevent a telescope from "getting in the way of itself." Coude-focus telescopes employ additional optical features, making them compatible with spectrographic equipment.
Radio telescopes, which were developed after the Second World War, are not only less expensive than equally-powerful optical types but can "see" objects that give off little or no light. The Hubble Space Telescope was launched into low earth orbit in 1990, allowing astronomers too view the universe from above the atmospheric disturbances that can affect ground-based astronomy telescopes. Great advances have also been made in amateur telescopes, from improved optics to computerized operation. Would Hans Lippershey ever be surprised!