Lenses bend (refract) light mirrors reflect light.Īgain, the blue arrows represent parallel rays of light hitting the primary mirror and reflecting off to hit the secondary mirror. What you’re really seeing is light being reflected.Īnd reflecting telescopes take advantage of the fact that light can reflect.Ī reflector has two basic parts, and they’re both mirrors. And things sure as heck don’t bounce off mirrors all the time when they’re “reflected” in them. Reflecting means the act of bouncing off something. Because in order for a cat to reflect off a mirror, it would have to do this: Well, obviously, a cat is being reflected in a mirror. And in order to understand them better, let’s take a look at another basic property of light. Most telescopes can accommodate just about any eyepiece after all, that’s the power of the eyepiece. They come to a focus-the focal point “f”-somewhere in the tube of the telescope.Īfter that, it’s the eyepiece’s job to make those rays of light parallel again and to magnify them the way you want. Refractors use convex lenses, lenses that are rounded outward on either side.Įach lens acts as a prism, and bends the light so the once-parallel rays are all aimed at each other. After all, light passes through them, and perfection is critical for aiming the light in the right direction. These lenses are little pieces of glass that have to be ground (shaped) absolutely perfectly. No, a telescope’s main job is to bring light to a focus. And you can change the magnification on any telescope just by swapping out the eyepiece. Wait…but I thought a telescope’s job was to magnify objects? You can see that the little piece at the end is the eyepiece.Īny telescope’s job is to bring light to a focus. That wider part at the up-pointing end of the telescope isn’t shown here, but all refractors have them. Here, the blue arrows represent rays of light reaching the telescope from some distant object in the sky. Here’s what basically happens inside a refracting telescope. Unfortunately, it also splits out the colors of the rainbow in the process, which is part of why refractors aren’t common in major research observatories. All these colors blended together creates white light.Ī refracting telescope takes advantage of the fact that light can bend. Because each color of light bends a different amount, it comes out the other end of the prism separated into distinct colors. The red light doesn’t get bent much at all. But light is made up of many different wavelengths, and each one bends differently. It passes through the prism, and along the way, it bends. In this animation, a white beam of light is aimed at a prism. And hey, guess what-that’s what refracting telescopes are named after. But how? How does white light turn into these colors? And you probably guessed that the light that forms rainbows is the exact same light that casts the bright, white beam of a flashlight. In order to better understand refractors, let’s take a look at one basic property of light. But what they do with light is more important. That same little tiny piece is tacked onto the side for the reflectors.Įvery reflector and every refractor can be recognized by these basic qualities. You’ll see that, not only is the end pointing up a bit wider than the rest of the telescope, but there’s a little tiny piece tacked onto the end. And you may notice that, unlike most of the rest, they’re not perfect cylinders. These two-the far left and the far right-are refractors. Take the two telescopes on either end of this lineup, for instance. They all look like cylinders, you say? Well…refractors are a little bit different. You can tell a reflector by its cylindrical design. Two very common types are reflectors and refractors, and each one in the image above is one of these. But they can all be sorted into a few basic types, and that makes choosing one a lot simpler. There are so many different varieties of telescopes, it can be hard to keep them all straight. Right next to light, the telescope is an astronomer’s most valuable tool.
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