Questions About Telescopes

How would you choose a telescope? Lets say – if you want to see the surface of the moon very closely.

If you want to look at details on the surface of the moon, any binoculars or telescope will give you stunning views. You will also be able to see the four Galilean moons of Jupiter and the rings of Saturn through just about any binoculars or telescope. However, if you are interested in looking at fainter objects, such as galaxies and nebulae, you will want to invest in a higher quality telescope or giant astronomical binoculars.

There are a few criteria that distinguish really excellent from okay telescopes:

The most important is the aperture of the telescope, which determines how much light the telescope can gather. You will be able to see bright galaxies and nebulae, such as the Andromeda Galaxy and the Ring Nebula, very clearly with a 6″ diameter telescope.

The following criteria are all important, but some are more or less important based on how you plan to use your telescope:

The second most important thing is a good mount. Your telescope must be stable so that it doesn’t wobble. This is not as important if you want to look at something big and bright like the moon, for which a pair of hand-held binoculars will do the trick.
The third most important thing is good optics. A reflecting telescope, which uses a mirror as its primary optic, is lighter-weight, cheaper, and suffers from fewer optical imperfections and aberrations than refracting telescopes, which use a glass lens as the primary optic. However, you can invest in a telescope or a pair of binoculars with high-quality glass.
Another criterion that I find important is the weight of the telescope. I am a small person and don’t particularly fancy carrying heavy loads by myself. I just bought a pair of giant binoculars and a tripod. Since the binoculars only weigh 10 lbs., I anticipate bringing them on many camping trips!

For a more detailed discussion of telescope features, see this Sky & Telescope article.