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A Basic Guide to Telescopes, Explaining How They Gather and Concentrate Light Rays

Updated on December 12, 2011

A telescope may be one of your favorite investments.

Everyone who owns a nice telescope knows how much fun they can be. If you're planning on buying one but want to make an educated purchase, check out the information I've put together below.

Looking through a telescope at the night sky.
Looking through a telescope at the night sky.

How to Calculate the Magnifying Power of a Telescope

You will see numbers printed on the telescope that tell you the width of the lens and the eyepiece. If the objective lens is 2000 mm and the eyepiece is 40 mm, divide 2000 by 40.

2000 / 40 = 25.

This means that your telescope magnifies the image 25 times.

Telescope aren't just for looking!

The other types of telescopes include radio telescopes that read radio waves, UV telescopes that see ultraviolet light, which humans cannot see, gamma ray, x-ray, infra red telescopes, and many more!

Below is a picture of a SKA (square kilometer array) site in Australia. These are powerful radio telescopes that are meant to pick up radio noise coming from space. These were featured in the movie Contact, which stared Jodi Foster.

Radio telescopes, SKA Australia
Radio telescopes, SKA Australia

Reflecting Telescopes

Almost all of the major telescopes used in astronomy are reflecting telescopes. There are many different designs, but I've included the most basic here so you can easily get an idea of how they work.

In this image, your eye would be at the focus of the telescope. The light is shown entering from the right, and hitting the primary mirror on the left. Notice that the primary mirror is curved, which causes the light rays to come together. The light hits the secondary mirror, which concentrates the light even more, sending it to you eye.

Reflecting telescope
Reflecting telescope

Refracting Telescopes

These aren't too common anymore. Check out the image below.

It shows the light entering the objective lens from the right. The objective lens bends the light so it comes together before entering the eyepiece lens. So, the refracting telescope and the reflecting telescope accomplish the same thing in two different ways.

refracting telescope
refracting telescope

Telescope Bits and Pieces

  • Some telescopes show the image backwards and upside down. This doesn't really matter, because whose to say whats up, down, front, and back when you're in the middle of space? However, if it bothers you, you can buy an eyepiece to correct this.
  • When purchasing your telescope, remember that you don't need the telescope with the biggest lens or longest body.
  • What you need is a good magnification and a sturdy tripod, without which you won't be able to see anything.
  • If you're not ready to invest at least $100 in a good telescope, don't buy one a cheap one from Wal-Mart, because it isn't worth your money.
  • You would be better off investing $50 in a nice pair of binoculars, which will also allow you to see many details of the moon's surface, the phases of Venus, Jupiter's moons, Saturn's rings, and much more.

Have fun!

Celestron 21061 AstroMaster 70AZ Refractor Telescope
Celestron 21061 AstroMaster 70AZ Refractor Telescope

This is the brand that my parents bought for me when I was 8. I'm now in my early 20s, and I still use it.



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