When we recommend
astronomy binoculars, the general guideline is to have a
binocular with enough image brightness to make it practical to see the faint objects that are often the targets in astronomy. This is generally defined as a binocular with an exit pupil (second binocular number divided by the first) of at least 4 or 5. Does this mean you cannot use a binocular with a smaller exit pupil, say an 8x20 compact binocular with an exit pupil of only 2.5 (20 divided by 8)?
The answer is that any optical instrument, even small compact
binoculars, will show you much more in the way of stars than you can see with your unaided eyes. Yes, even a small binocular is better than no binocular for
astronomy. If you own a small binocular, take it out and start doing some astronomy, right now. You'll be that much ahead in learning the sky when your astronomy binocular arrives.