While the unaided eye or binoculars can reveal much of the night sky, a telescope reveals so much more. Seeing Saturn’s rings or the Moon’s craters with your own eyes can be an “oh wow” moment.

Buying a telescope is a big step, especially if you’re not sure what all those terms — f/ratio, magnification, go-to — mean. So, to eliminate confusion and make sure you understand what you’re buying, ...