As worn by the astronomer? (5)
I believe the answer is:
jeans
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for jeans that I've seen before include "article of clothing" , "Denim trousers" , "Are they worn by girls in Britian" , "Strides casually" , "(Usually) blue casual wear" .)