Binoculars are very commonly used in astronomy. A lot of people think, to do “real” astronomy, you must have a telescope. Not so. A lot of deep sky objects are within the grasp of normal binoculars.
First, a little about binoculars. A binocular’s size is in two numbers (#x#), for example, 7×50. The first number is the amount of magnification, in 7x50s, 7x (or the image is magnified 7 times). The second number is the aperture, the objective (main) lens’s diameter in millimeters. In 7x50s, each objective has 50mm of aperture. (Also, Sky and Telescope magazine contributing editor Gary Seronik wrote this helpful article on binocular exit pupils).
For astronomy binoculars, the more aperture is better (of course, if you read Gary Seronik’s article, you will see that more magnification is desirable with more aperture). What makes binoculars good for astronomy? There are multiple reasons that make binoculars good for astronomy. One of them is the fact that they use both eyes, as opposed to a telescope. Using two eyes, the brain merges the light from the binoculars, making a brighter image. Using two eyes can also bring out colors. Binoculars are liked for their wide-field view, showing good expanses of sky (this of course depends on the magnification). But as aperture and magnification goes up, so does the weight. For good views, binoculars can be tripod mounted. My 15x70s are at the very limit of hand holding for me; many consider 10x50s the limit.
High portability makes binoculars great for traveling astronomy. They are much smaller than a lot of telescopes. There are some advantages to telescopes of course, such as more aperture; I can’t see M1 in my 15×70 binos, but can in my telescope.
Do astronomy binoculars have to be expensive to be good? Not at all. Of course, higher quality will always be higher quality (and usually expensive), but even inexpensive binoculars work very well. Most binoculars, at the edge, will show a degraded image, aberration, or coma (when stars look elongate, like commas “,”) of some sort, and higher quality binoculars have less to none. But usually as long as they come well collimated, are sharp towards the center, and focuses well, they’ll work well enough for budget astronomers.