Buying Telescopes
Most beginners trying to buy a telescope quickly discover that it's surprisingly hard to do. There are countless telescopes ranging in price from about $50 to tens of thousands of dollars, and the advertising makes them all seem wonderful. Let's try to simplify it!
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Types of Telescopes
There are three basic types of telescopes that are suitable for beginners.
Refractors have a lens on the end that you point at the sky, with the eyepiece at the far end of the telescope tube. They make an image by bending ("refracting") light through the lens. Good ones tend to be expensive, and cheap ones aren't very good.
Reflectors are open at the "sky end." A curved mirror at the other end reflects light to a small secondary mirror, which reflects light into the eyepiece. The eyepiece holder is near the top of the telescope. Reflectors tend to be less expensive than the same diameter refractor.
Schmidt-Cassegrains are a popular type of catadioptric telescope. They have a correcting plate at the front and a curved mirror at the back. The mirror reflects light to a secondary mirror inside the correcting plate, which reflects the light through a hole at the center of the primary mirror to the eyepiece. They are optically long telescopes in short tubes, and very portable. They tend to be of high quality and pricey.
Telescope Mounts
There are three basic telescopes mounts for beginners, and a fourth type to avoid.
A sturdy mount that does not shake may be the most important part of the telescope, but is often overlooked. If the mount shakes when you touch it, or when the wind blows, the best optics in the world will still give a poor view! All of the mounts mentioned here can be found on telescopes suitable for beginners—don't let the size of some of these telescopes bother you.
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Dobsonian mounts look similar to boxes that sit on the ground or a sturdy table. They are simple, generally sturdy, and inexpensive. The drawback is that they allow the telescope to move only up and down and sideways. However, since celestial objects appear to move at angles and on curves as Earth rotates, following a star or planet means frequently moving the telescope in two different directions (two ways to make a mistake). Despite this, they are popular mounts and easy to use with practice. They make many telescopes more affordable to beginners.
German Equatorial Mounts (GEMs) allow telescopes to follow celestial objects with one easy motion. The trade-offs for that are increased complexity, increased weight, and increased cost relative to a Dobsonian mount. Many GEMs can be motorized to follow objects, and high-end versions can be computerized to find and track objects automatically. Expect to pay $500 for a basic GEM and $1000 or more (sometimes much more) for computerized versions. GEMs can be complex to set up, but then are easy to use in long observing sessions .
A fork equatorial mount holds the telescope with one or two tines, vaguely resembling a dinnerware fork. Like any equatorial mount, it allows the telescope to follow a celestial object with one motion. Fork mounts can be motorized or computerized, and are very common on Schmidt-Cassegrain telescopes.
And finally, a mount to avoid!
Altitude-azimuth mounts (also called "alt-az" or "alt-azimuth" mounts) move the telescope only up-and-down (altitude) or sideways (azimuth). Alt-az mounts like the one pictured, shaped like a squared-off horseshoe with (or without) a chrome connecting bar, are typically found only on the cheapest telescopes. They can be very shaky and nearly impossible to aim, and make focusing or tracking a celestial object nearly impossible. Toy telescopes with mounts like these can't be recommended—there are other options even in their very low price range. Even very reputable manufacturers make them, and they are unfortunately easy to find. The only decent alt-az mount is the Dobsonian mount.