Telescope Buying Guide Part 3: How to Use a Telescope

by Joe Rao, SPACE.com Skywatching Columnist

Date: 24 November 2009 Time: 12:48 PM ET

Before anything else, if you have just bought a telescope, invest in a couple of good books on the stars and constellations (suggestions at the bottom of this page). As the late George Lovi (1939-1993), a popular astronomy writer once wrote: "First spend some time learning the sky with your own personal optics – the set nature mounted in your head."

It's always been my belief that you should not hastily rush outside with a telescope before not even knowing what's in the sky or what to look at. It's akin to buying a catamaran if you've never sailed before.

When you finally start setting up your telescope, take whatever time is needed to learn its use and operation. All those knobs and levers are there for good reason. Be sure that you have assembled everything with great care.

Your first session should be during the day.

Practice how to aim and focus your new instrument not on the night sky, but on daytime terrestrial objects. Not only are they bright and easy to see, but unlike night sky objects they will not drift out of your field of view because of the rotation of the Earth.

Picking your power

Telescopes typically come with multiple eyepieces that can be swapped out to change the power setting. But you need to understand some limitations.

The general rule of thumb is that the maximum amount of magnification for any telescope is 50 power per inch of aperture. So if you intend to buy a 6-inch reflector, 300-power is as high as you should ever attempt to go; the maximum for a 3-inch refractor should be 150-power.

In fact, you'll probably be surprised to discover that your most pleasing views will come at much lower powers.

Staying safe

Never, ever, look directly at the sun at any time with your telescope.

If you do wish to observe the sun, the only completely safe way (especially for the beginner) is to project its enlarged image onto a white card or screen.

Some department store telescopes may include a dark glass that is designed to screw into the eyepiece of the scope. Supposedly, this filter is to be used to view the sun. If your telescope comes with such a device, discard it immediately!

By pointing your telescope toward the sun, its light and heat are tremendously intensified when it reaches your eyepiece. As such, there is an ongoing threat that the filter will be heated to a point where it will suddenly crack. The end result for you can be partial or total blindness.

Suggested Reading

Below we have included a small sampling of books, which you might want to consult on various aspects of stargazing with the naked eye, binoculars and telescopes. Whether you're just starting out in astronomy or a seasoned sky watcher, we hope you find all this interesting and informative.

For Naked Eye Observing

Starlight Nights. The Adventures of a Star Gazer. By Leslie C. Peltier. Sky Publishing Corporation, 2000 (Third Printing).

Stargazing: Astronomy without a Telescope. By Patrick Moore. Cambridge University Press, 2000

Nightwatch: A Practical Guide to Viewing the Universe. By Terence Dickinson, Adolf Schaller, Victor Costanzo, and Roberta Cooke. Firefly Books, 1998.

40 Nights to Knowing the Sky. By Fred Schaaf. Owl Books, 1998.

Secrets of the Night Sky: The Most Amazing Things in the Universe You Can See with the Naked Eye. By Bob Berman. Harperperenial Library, 1996

Skywatching. By David H. Levy. The Nature Company/Time-Life Books, 1995.

The Stars, A New Way to See Them. By Hans Augusto Rey. Houghton Mifflin Company, 1976.

Books on Binoculars

Exploring the Night Sky with Binoculars. By Patrick Moore. Cambridge University Press, 2002.

Stargazing with Binoculars and Telescopes. By John Mosley. McGraw-Hill, 1998.

Exploring the Night Sky with Binoculars. By David Chandler. David Chandler, Co., 1994.

Binocular Astronomy. By Craig Crossen and Wil Tirion. Willmann-Bell, 1992.

How to Choose Binoculars. By Alan R. Hale. C & A Publishing, 1991.

Touring the Universe through Binoculars. By Phillip S. Harrington. John Wiley & Sons, 1990.

Books on Telescopes

The Nexstar Users Guide. By Michael Swanson. Springer, Second Printing, 2005.

Starware. By Phillip S. Harrington. John Wiley & Sons, 2002.

Astronomy with Small Telescopes Up to 5 Inch, 125 mm. By Stephen F. Tonkin. Springer Verlag, 2001.

The Cambridge Guide to Stargazing with your Telescope. By Robin Scagell. Cambridge University Press, 2000.

Telescopes and Techniques. By C.R. Kitchin. Springer Verlag, 1996.

How to use an Astronomical Telescope. By James Muirden. Simon & Schuster, 1988.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.