How Do Telescopes Work
Before I answer the question, "How do telescopes work?", it might do well to point out that there are actually different types of telescopes. For instance, there are optical telescopes, radio telescopes, and even high energy telescopes such as X-ray and Gamma-ray telescopes.
Although these devices, regardless of the type, all make use of electromagnetic waves, the band of electromagnetic waves on which these telescopes operate on differ. Optical telescopes use waves in the visible spectrum, radio scopes use radio waves, and X-ray and Gamma-ray telescopes use X-rays and Gamma-rays respectively.
As such, their workings also differ.
In this article, in answering the question, "How do telescopes work?", I shall be focusing on simple optical telescopes. There are two simple kinds of optical telescopes: refracting and reflecting telescopes. Other similar devices that also use waves near and in the visible spectrum include catadioptric, infrared, submillimeter, ultraviolet, and Fresnel telescopes, but we won't be discussing them here.
Refracting Telescope
The refracting telescope is the oldest type of telescope. Galileo Galilei, who studied the skies in the 1600s, used a refracting telescope which he himself constructed. A basic refracting telescope has two lenses: an objective lens that points to the object being studied and an eyepiece through which the observer peers through.
Light from the object strikes the objective, proceeds into the eyepiece behind it, and then enters the observers eyes. As its name implies, a refractive telescope refracts (changes the direction of) light to produce a magnified virtual image of the object. The object is usually inverted. However, since astronomical telescopes are directed at objects devoid of tops and bottoms, this inconvenience usually goes unnoticed.
Reflecting Telescope
The extensive use of lenses in refracting telescopes presents a substantial number of disadvantages. Large lenses can be extremely heavy, susceptible to aberrations, and can be deformed due to gravity. For these reasons, many astronomers prefer reflecting telescopes over the refracting types.
Reflecting telescopes make use of curved mirrors (hence the term 'reflection') to direct captured light into the observers eyes. To construct a really large reflecting telescope, an array of adjustable mirrors can be used. If there are any distortions, they can be easily corrected by simply adjusting the mirrors.
Although there are numerous variations of the reflecting telescope, each kind reflects light to produce an image. The configuration of some of the models allow them to project upright images.
We've got so many articles about telescopes here in Universe Today. Here's one link that will direct you to a long list:
Telescopes
There's more from NASA
NASA's Largest Space Telescope Mirror Will See Deeper Into Space
Mirror Production Begins on Webb Telescope
Here are episodes from Astronomy Cast you might be interested in. Lend us your ears!
Shooting Lasers at the Moon and Losing Contact with Rovers
The Moon Part I
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