Yikes! By all means study anything else than law!!! Just kidding. Actually, so long as the population continues to increase there should always be a market for one more lawyer. It depends on where you are living I suppose. In the USA we have on a per capita basis far more lawyers than we need, and our society has become a very contentious one where everyone seems eager to rush into the court system to solve problems.
As for astronomy, we are already experiencing a glut of astronomers compared to the number of high quality jobs available. I think we have twice as many astronomers as the market can support, and as a consequence there are a lot of 1 and 2-year positions out there taking advantage of the labor market.
I would strongly recommend seeing your education in astronomy as a stepping stone to other professions in computers and applied physics; although applied physicists are now becoming ubiquitous too!!
Learn a skill ( computer programming, statistical analysis, engineering) while you are learning cosmology and astrophysics. This is your best insurance that you will have something to fall back on just in case you are not one of the lucky few to secure a stable job in astronomy.