Telescopes are the oldest gadgets used by man for watching the sky. The use of optics dates back to the thirteenth century, but early seventeenth century Telescopes are invented by Dutch opticians.
Galileo Galilei was the first scientist who used the telescope in (1564-1642), inventor, among other things, a telescope model that still bears his name. The use of this instrument allowed Galileo see four satellites of Jupiter (the four largest moons, now called Galilean)
Telescopes are instruments to magnify images of distant objects such as stars. Currently, there are different types of telescopes (refractor, reflector, multiple mirrors, giant radio telescopes), which are highly specialized and work in a variety of ways.
This type of telescope has a relatively thin with the main Lens (objective) on the front, which collects and focuses light.
This simple type of telescope has two lenses. Both are convex; i.e., thicker in the center than at the ends. The lens closest to the object is called target. The light from a distant source passes through the lens and reaches a focus as a ” real “and reversed inside the telescope tube image. The eyepiece lens magnifies the image formed by the objective.
In an astronomical telescope, the ” virtual “image formed by the eyepiece is reversed.
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Instead of lenses, this telescope uses a large, heavy concave mirror to collect and focus light. You look through the eyepiece located on one side of the tube near the upper end.
The light from distant objects like stars enters into the telescope tube in parallel rays, then reflected by the concave mirror to a flat mirror diagonal. The diagonal mirror reflects the light through an opening in one side of the telescope eyepiece lens to a tube.
Reflector telescopes may be greater than refractors because the curved mirror can be supported over its entire surface while a big lens can be supported only at their ends.
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They are also called complex telescopes. They use lenses and mirrors. The goal is a concave mirror, but the aperture is a corrector lens also holds a secondary mirror. The tube is wide and short; the eye is located at the rear end of the lens. Retro-reflectors are powerful, high-quality instruments thanks to a more complex design enjoy a compact size and therefore easier to transport and handle.
If you are struggling in choosing between these model please read this article: What is the best telescope for Astronomy
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The radio telescope is a set of devices used for the study of the universe by capturing electromagnetic radiation from celestial bodies like the sun, the stars, and other stellar phenomena.
Radio telescopes have a satellite dish-shaped antenna that picks up radio signals from cosmic space. These signals are fed to a receiver to be decoded by a computer and get the image of bodies and cosmic phenomena.
Achromatism, optics, owned by a lens system which deflects a beam of white light so that all component colors focus on the same point, so that a sharp image is obtained.
A single lens can not achieve an achromatic approach because light of different wavelengths suffers when passing through a different lens deviation. To achieve an achromatic approach must be used at least two glass lenses with different refractive indices.
This principle was discovered in 1757 by John Dollond, a British optician.
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