Distinguish from
天文学 (tiānwénxué, 'astronomy', the study of celestial objects).
宇宙学 is the more theoretical sub-field about the universe as a whole. Both translate loosely as 'studying space' but
宇宙学 is what you'd use for Stephen Hawking (
霍金 Huòjīn),
天文学 for someone running an observatory.