People have long looked to the stars for answers to numerous questions. What exists beyond planet Earth? Are humans the only intelligent life in the universe? What do other planets look like? In order to answer these questions and many more, craftsmen and scientists built and perfected telescopes made to search the heavens for answers. Different types of optical telescopes were invented over time to help mankind search the heavens.
Galileo is credited with perfecting the first optical telescope used in astronomical exploration, improving on the design of spectacle-makers and opticians. The Galilean telescope is classified as a refractor, the earliest and simplest optical telescope type created. Refractors work by bending light when it passes through a lens set at the front of a long tube. All light rays meet at the back of the tube, converging on the eye of the viewer. These telescopes are cheaper than the other types and are simpler to make than later varieties of telescope.
Refractors, however, had several flaws, one of which is the distortion--called chromatic aberration--that occurs when lights of different wavelengths come to focus in different places within the tube. Isaac Newton solved this problem by inserting mirrors in the telescopic tube, inventing the reflector telescope. Some of these mirrors decrease the amount of light that enters the telescope, but the increase in clarity is outweighs the decrease in light. These telescopes are good for beginners and experts alike and are used in numerous small and large-scale astronomical explorations.
Reflectors enable the construction of large telescopes with sizable reflectors built in them. Scientists learned that they could get better results with a large collection of smaller mirrors than they could with a small number of larger mirrors. These large telescopes have taken clear pictures that have astonished scientists and the general public with their content. Size and number of mirrors, however, are not the only factors involved with the clarity of telescopic photographs.
The Space Age presented astronomers with opportunities never before open to them. In 1990, NASA launched the Hubble Space Telescope into orbit, the world's first space-based telescope. Images obtained from outside the Earth's atmosphere are clearer than those captured beneath it because the atmosphere is constantly moving and shifting. This movement causes blurring referred to as 'seeing,' but this blurring is not present in Hubble photographs due to it being beyond the Earth's atmosphere. The Hubble will be replaced by the newer, more modern James Webb Space Telescope that will have enhanced visual and infrared viewing capabilities.
Other types of telescope are the catadioptric and infrared telescopes. The catadioptric telescope makes use of both reflection and refraction to capture images and is generally contained in a more compact design than is often used for other telescopes. The Schmidt-Cassegrain model is the most popular catadioptric telescope and is quite popular with astronomers due to its image quality. Infrared telescopes see limited use because they are only effective in chilled regions and areas shielded from heat. They are used to detect emitted radiation in the electromagnetic spectrum and come in ground-based, air-borne, and space models.
As mankind continues to explore space, scientists will continue to develop new and improved optical telescopes to aid in that exploration. Professionals and amateurs alike will always be searching the heavens for the secrets of the universe.