Most of us, at some point or another, have asked themselves how telescopes work. However, we might have gotten an incomplete or inaccurate answer, or even none at all. Another complication is the fact that there are several different types of telescopes, including those for seeing gamma rays, those that use mirrors, and those for looking at infrared and ultraviolet light. However, for the purposes of the question, we'll limit the discussion to the kind of telescope most of us think about – the optical telescope.
How Telescopes Work
Even optical telescopes – those that show us light that can be seen by the naked eye, come in more than one type. There are refracting telescopes, reflecting telescopes, and compound telescopes. The first uses lenses, and is the type developed hundreds of years ago by Galileo. The second uses mirrors, and was developed in the seventeenth century and later refined by Isaac Newton. The last is a combination of the two methods, designed to reduce problems caused by each one.
However, no matter which kind of optical telescope you're talking about, they all use the same basic principle. Telescopes work by collecting light from objects that are in the sky, or terrestrial objects at a distance. The light is then focused, either by being bent through lenses or reflected from mirrors. The focused light them forms a clearer image than we could see with our naked eyes.
Telescopes come in many strengths and sizes, with the extremes ranging from children's dollar store toys to the Hubble Space Telescope. At home, you'll probably use something in the middle, but even amateur telescopes can be very powerful. A six inch telescope can allow you to read a dime from as much as a hundred fifty feet away. In general, telescopes with larger objective (far end) lenses are able to gather more light, creating a brighter image and providing more information for the magnifier. Magnification depends on the telescope's internal lenses and mirrors.
Depending on the method used, however, the way telescopes work can introduce problems into the image. For instance, most refracting telescopes suffer from chromatic aberration – a rainbow halo you might see around bright objects. More expensive models correct this by using a special lens. Reflecting telescopes don't have this problem, but can suffer from distortion around the edges of the image. They are much less expensive, however, and are a lot easier to build at home. Which kind of telescope you use will depend in part on your budget, and what you need to look at. Look around to see how various telescopes work and pick the best one.
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