Comparing the Different Types of Telescopes

There are three different types of telescopes used by amateur astronomers: reflecting, refracting and solar. All three concentrate light and magnify it so that you can see distant objects, such as planets and constellations. If you're new to astronomy, understanding how these telescopes work can help you choose the one that's best suited for the types of objects you wish to view.

Refracting Telescopes
A Dutch eyeglass maker named Hans Lippershey invented the first refracting telescope in 1608. While working in his shop, he discovered that viewing a distant object through a concave lens and a convex lens held in front of one another caused the object to be magnified. Working with this idea, he placed the two lenses in a tube and the first refracting telescope was born. In 1609, Galileo Galilee improved upon Lippershey's design and was able to study objects in space with his refracting telescope.

A refracting telescope works similar to a magnifying glass. It uses a convex lens to bend light and bring it into focus. By using a lens that is thicker at the center and thinner at the edges, the light focuses on a particular spot known as the focus point. Light concentrates at the focus point because it bends more at the edges of the lenses and less in the center. When you look into the eyepiece, a concave lens magnifies the image at the focus point, bringing it sharply into view.

While a refracting telescope works quite well, there are a few problems with it. First, the images may not always be clear because of the bend in the light. Second, the size of the lens is limited. Since the lenses are made of curved glass, at a certain point they become too big to be practical. This limitation in lens size limits a refracting telescope's viewing power. Refracting telescopes are larger, heavier and more expensive, and their lenses must be kept in precise alignment for them to work properly. They're best suited for viewing nearby objects in space, such as planets.

Reflecting Telescopes
The reflecting telescope was invented shortly after the refracting telescope. In 1669, Isaac Newton began working on a reflecting telescope. He believed that using mirrors would let a telescope gather more, thus bringing distant objects into better focus. Newton also added an additional reflector in his design. This secondary diagonal mirror, which located near the primary mirror, allows the image to be viewed with an eyepiece mounted on the side of the telescope. This side eyepiece provides an unobstructed view of the image.

With a reflecting telescope, the gathered light reflects from a large concave mirror onto a secondary mirror. Once the image hits the secondary mirror, it can be viewed through the eyepiece lens. The mirrors are precisely made and must be properly positioned for the reflecting telescope to function correctly. In practice, it's much harder to knock the mirrors in a reflecting telescope out of alignment than it is to misalign the lenses of a refracting telescope.

A reflecting telescope is the one most commonly used tools in astronomy. They're much lighter and cheaper than refracting telescopes. They tend to work better for urban stargazing, since their mirrors collect more light. They're also have a larger field of view than refracting telescopes, making them ideal for viewing constellations and groups of stars.

Solar Telescope
The solar telescope is specifically designed to view the sun. The design considers the sun's optical wavelengths and the danger that would be posed if an observer looked directly at the sun. Solar telescopes employ lenses with special coatings and filters that allow you to view the sun safely.

You typically don't look through a solar telescope; rather, the image is projected on a surface or viewed indirectly. Different types of filters can allow you to see different aspects of the sun, such as the winds on the solar corona or sunspots. A solar telescope can be used anywhere, but stationary models need to be placed carefully, since the sun is constantly moving across the sky. You'll need a location that offers an unobstructed view of the sun for an hour or more to follow its motion and keep it in view.

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