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.
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.Radio telescopes, like the
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.
- How do I polar align my telescope? (Beginner)
- What kind of telescope should I use for astrophotography? (Beginner)
- Where can I see Newton's original reflecting telescope? (Beginner)
- Why is the Hubble Space Telescope in space? (Beginner)
- Why are telescopes kept in cold conditions? (Beginner)
- Why is NASA shutting down the Hubble Space Telescope? (Beginner)
- Where is the Spitzer Space Telescope? (Beginner)
- Why do astronomers use telescopes? (Beginner)
- What colors are visible through an amateur telescope? (Intermediate)
- Is it possible for amateurs to do optical interferometry? (Intermediate)
- How does interferometry work? (Intermediate)
- What are the advantages and disadvantages of using a telescope in space? (Intermediate)
- What are the largest radio wavelengths observed from radio sources in the sky? (Intermediate)
- How is it that we see farther out in space (farther back in time) than in the past? (Beginner)
- Can you give me advice on buying a telescope? (Beginner)
- Can I see details on Venus? (Intermediate)
- What kind of eyepieces do I need to look at planets? (Intermediate)
- Why do pictures of distant galaxies have higher resolution than those of nearby planets? (Intermediate)
- Why are telescopes located in remote places? (Intermediate)
- What equipment do I need for astrophotography? (Advanced)
- How can I contribute to science as an amateur astronomer? (Advanced)
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.
How to ask a question?
If you have a question about another area of astronomy, find the topic you're interested in from the archive on the side bar or search using the below search form. If you still can't find what you are looking for, submit your question here.