No discussion of how telescopes work would be complete without exploring the many various forms of telescopes, as not all telescopes work alike. Yet all telescopes share on thing in common - they collect radiation. Often this radiation is in the form of light. Telescopes have the additional tasks of enhancing the resolution of an object by increasing its apparent angular diameter, and determining the location of the observational target in relation to its surroundings.

'Optical' telescopes collect light along the visible spectrum and relay that information to either the viewing human eye, or to a camera or computer for future study. There are several types of optical telescopes, depending on whether mirrors, lenses, or a combination of both to collect and relay data.

'Radio' telescopes collect light along the electromagnetic spectrum far beyond the small light range that we can see. Other telescopes may monitor X-Rays, microwaves, gamma rays, or other forms of radiation. Various instruments such as polarimeters, photographic plates, and photometers are used along with telescopes to enhance, amplify, correct, or record the imagery.

OPTICAL TELESCOPES

The most commonly used telescopes in visual astronomy are 'reflector' telescopes. Commonly called 'mirror telescopes', these use two mirrors to capture light and then reflect it in a focused beam into an eyepiece or onto a photographic plate. The first mirror is usually parabolic - i.e. it is shaped into a concave parabola. Sometimes the mirror is spherical, but the parabolic mirrors are more common.

Light enters the telescope and hits this first mirror which is positioned at the very back of the telescopic tube. The nature of the parabolic mirror is such that all light hitting it strait on is reflected back to a single point. This point is the 'focus' of the parabola. By changing the shape of the parabola, the focus can be changed, allowing reflector telescopes to be many lengths and sizes. The focus point is situated behind the secondary mirror, so all light bouncing off of the first mirror hits the second.

The second mirror, unlike the first, is either a convex hyperbola or it is flat. Reflector telescopes that use a secondary flat mirror are called Newtonian Reflectors after their inventor - Sir Isaac Newton. The flat mirror is at an angle, and reflects the light out the telescope's eyepiece. Newtonian telescopes are usually smaller telescopes compared to the ones using a hyperbolic secondary

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