How much chemistry do astronomers use. To be an astronomer, you generally need a degree in physics, so

compared to physics, how much chemistry do they use.

I majored in astronomy and physics, and am now an astrophysicist. I haven't taken a chemistry class since high school. That's not to say I don't use chemistry, since chemistry is basically a step up from particle physics, but I don't know all that much about it. Most astronomers don't. But there is a small field of astrochemistry, and many laboratory astronomers (relatively new field) have more chemistry training.

Compared to physics, almost none.

But you DO need to be conversant (able to talk about it) if you are looking for things like signs of life, as you need to be able to understand things like the spectrum of various elemens in order to determine if these elements are in the atmosphere of a planet, and thus that planet may or may not be capable of producing life.

Depends what is their major interest.

Little or none is needed for the study of galactic clusters and collecting observational data from variable stars, comets and binary systems. OTOH chemistry would be a major component of the expertise set of those involved with the study of planetary surfaces and atmospheres.

All too often, armchair astronomers and pop-scientists attempt to explain geological or climactic features of planets such as Mars, Titan or Europa with little or no understanding of the chemistry involved. The performance can be quite laughable, and their conclusions worthless.

Essentially if any form of condensed matter is being subject to study, then chemistry must be one of the main subjects to be understood if any meaningful analysis is to be made.

Cheers!