"He studies astronomy".
Astronomy is a long word.
My brother is studying astronomy.
When it is at the start of a sentence.
I want to study astronomy later on in life.
I like the study of Astronomy. Of course.
He always dreamed of astronomy as his future profession, but he became a doctor instead.
When I hammered the nail, I accidentally hit my thumb. The astronomy teacher hammered the basics of star formation into our heads over and over again.
No, it shouldn't all be uppercase, and it doesn't need to be capitalized unless it is the first word in a sentence or part of a title.
You can use the word Truss in a sentence like this.
Can you use the word concluding in a sentence? Done.
Just use it! Or do you mean, can you use the word beheld in a sentence.
I don't believe in astrology. Astrology and astronomy used to be the same science.