Get Small

For a given aperture, reflectors (which gather light using a mirror at the bottom of the main tube) are generally the least expensive of the three basic designs, but they’re also the largest and require periodic adjustment of their optical alignment — especially if they’re moved around a lot. Refractors (which have a lens at the front of the tube) have somewhat greater ruggedness and maintenance-free optics, but they get expensive fast as the aperture increases. Compound or catadioptric telescopes, which use a combination of lenses and mirrors, offer compact tubes and relatively light weight; two popular designs are called Schmidt-Cassegrains and Maksutov-Cassegrains.

Any telescope must have a sturdy, smoothly working support. Many scopes come with mounts, but others, especially small ones, are sold as optical tube assemblies only (called OTAs). If you buy one of these, you’ll need to supply your own mount. Luckily, smaller telescopes often come with a mounting block that allows them to be attached to a standard photo tripod with a single screw.

But beware: A tripod that’s good enough for taking family snapshots may be too wobbly for astronomy. As a very rough rule of thumb, a photo tripod will support its own weight nicely when used for astronomy. If the tripod weighs more than the scope, that’s better still — I even try for a weight ratio of 2:1 or more if possible. And while a common photo tripod might work well with smaller scopes, once the aperture hits 3 inches and larger, you'll probably need a specialty telescope mount to get enough steadiness. Here’s another consideration: the higher powers afforded by compound telescopes require even more steadiness and thus a sturdier mount — which may negate the size advantage of their compact tubes.

Mounts designed for telescopes usually forgo the single-screw attachment in favor of larger, more robust rings or dovetail-attachment plates. On some mounts the scope swings left-right and up-down, just as on a photo tripod; these are altitude-azimuth (or simply altaz) mounts. A more involved mechanism, designed to track the motion of the stars by turning on a single axis, is the equatorial mount. But equatorial mounts tend to be larger, heavier, and more complicated, which may take them out of the running for travelscope consideration.

Finally, remember to leave room for your accessories: eyepieces, extra batteries, any tools needed, your star atlas and sky guidebook, notebook, pencils, and a dim red flashlight so you won’t ruin your night vision. Many manufacturers make custom cases for their telescopes, often with spaces for accessories.

When sorting through all these possibilities, remember that a small telescope that gets used often will show you more than a large one that gathers dust in the garage waiting for that perfect night when you have lots of time. This is especially true of a travelscope. A small, lightweight scope will tend to get used more. And the less setup you have to do, the better. Best of all is a telescope that can be packed and picked up in one piece with one hand.

Other Options

Not enough room for a telescope of any size? Binoculars are a great astronomy tool. For stargazing, you want binoculars with front lenses at least 30 mm across, preferably 50 mm. (How can you tell what you’ve got? Near the eyepieces you’ll find two numbers separated by "x". The first is the magnification; the second is the diameter of the front lenses in millimeters.) I consider 8x50 binoculars best for general-purpose viewing at night. But even modest 7x35s can show you bright, well-known trophies like the Andromeda Galaxy, the Orion Nebula, and the Pleiades cluster — often even out of a hotel window.

On the other hand, if you're planning on staying someplace for a while, forget about packing a scope and ship it instead! Most hotels will hold packages for you at the front desk. If you’re going to a remote location, try shipping to one of those packaging stores (like the "UPS Store"); these will generally receive and hold packages for a small fee, if any. This way you can ship a larger scope than you’d be able to carry on a plane and saves the hassle of dealing with large cartons at airports (and unpacking and explaining a strange metal tube to airport security). Be sure to save all the packaging that your scope arrives in — you’ll have a ready-made shipping container if the need arises.