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Spitzer Space Telescope
Credit: Russ Underwood, Lockheed Martin Space Systems
The Spitzer Space Telescope was launched on August 25, 2003 and is designed to detect infrared radiation (or heat) from distant objects in space. Spitzer will use both images and spectroscopy to study cooler objects in space (e.g. small stars and molecular clouds) and to see into dust shrouded regions, like newly formed planetary systems and the centers of galaxies. The image above shows the 0.85 m (2.8 foot) telescope under construction at Lockheed-Martin. You can find more images and information at the Spitzer Space Telescope website.
Messier 81
Credit: NASA, JPL-Caltech, K. Gordon, S. Willner & N. A. Sharp
A Spitzer Space Telescope image of the galaxy M81. M81, located 12 million light years from Earth, is a familiar object to many amateur astronomers because it is easily observed with binoculars or a small telescope. Spitzer is able to "separate" various components of the famous galaxy by taking images in different infrared colors. In this composite image, blue traces the distribution of stars in the galaxy, green shows dust that has been heated by nearby stars, and red is emission from warm dust surrounding very massive stars.


Telescopes are one of the main ways that astronomers (both professional and amateur) explore the universe. They come in all shapes and sizes depending on their function. Generally, bigger telescopes are better if you want to see faint, far-away things, because they can gather more light and have better resolution. Resolution is the ability of a telescope to discern objects close together; for example, the ability to clearly separate two stars that are very close together or the ability to see smaller craters on the Moon.

Visible Light Telescopes

The telescopes that most people are familiar with are visible-light (optical) telescopes. There are two main kinds of optical telescope, refractors and reflectors. Refractors use lenses (like you find in eyeglasses or binoculars) to collect and focus light. However, large pieces of finely ground glass are expensive and heavy, so it's not practical to make large refractors. Yerkes Observatory in Wisconsin is the largest refractor ever made and has lenses that are 40 inches in diameter.

Reflecting telescopes use mirrors to focus light, and since they are cheaper they can be made much larger. All major astronomical telescopes built now are reflectors. The largest optical telescopes are currently the Keck telescopes that have 10 meter mirrors and the brand new Gemini telescopes that have 8 meter mirrors.

Seeing the Universe at Different Wavelengths

Although optical telescopes are the type most commonly used for stargazing and amateur astronomy, lots of astronomical research is done on telescopes that look at other wavelengths of light. Each of these wavelength ranges shows us something unique about the universe and allows us to view events and objects that can't be seen with human eyes.

Radio telescopes, like the Very Large Array and Arecibo Observatory, look at very long wavelength light. Radio waves are so large that they don't notice small imperfections in the telescope surface, so unlike optical telescope mirrors, radio telescopes often have dishes with lots of holes to reduce the weight. You can see many diverse things with radio telescopes; for example, you can investigate how hydrogen gas is distributed in our galaxy and other galaxies, and you can time the rotation period of pulsars.

Telescopes operating at very short wavelengths, like X-Rays and Gamma Rays, have to be located in space since our atmosphere blocks radiation at these wavelengths. At short wavelengths, you see regions where high energy radiation is being created. Some of these places include stellar explosions, galactic centers, and regions near pulsars and black holes. The Chandra X-Ray Observatory is one telescope that looks at these objects.

Many questions we receive about telescopes relate to amatuer observing. Before writing in with your telescope question, please remember that we don't know specifics about small telescopes unless we happen to have used the exact same thing. Check with manufacturers for telescope-specific problems or questions. Also, please explore our archive of telescope questions and our favorite links about telescopes before writing in with your question.

The Ask an Astronomer team's favorite links about Telescopes:

  • Sky and Telescope This web site has star charts you can download, information about planets currently visible, and articles about purchasing and using telescopes. Look at the How To section first if you are thinking about buying a telescope or want to get started using your new telescope!
  • How Telescopes Work This site goes through the basic types of optical telescopes and how they work.
  • Hubble Space Telescope Outreach See Hubble Space Telescope pictures, check out where Hubble is right now, read about how images are produced, and play some games.
  • National Radio Astronomy Observatory NRAO's introduction to radio astronomy and radio telescopes. A fairly advanced tutorial covering all areas of radio astronomy.
  • Telescope review web site. A detailed review of over 100 telescopes for amateurs.

Previously asked questions about Telescopes:

How to ask a question:

If you have a question about Telescopes which isn't answered above, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.

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