An astronomical unit is the distance between Earth and our sun.

Although it was a great hobby for her, she wanted to study aeronautics or astronomy as a career.

If that really is where is came from, it would have had to be a pretty powerful astronomical event - or an advanced alien civilisation using an astonishingly large and powerful transmitter.

Jane is one of my most astute coleagues. She teaches a course in astronomical phenomenon.

In other words, how many total system states are there with a particular energy. Well, in many, many, many cases the answer is some astronomical number.