Astronomy is a branch of science that studies objects outside the atmosphere of Earth, and the motions and nature of these objects. According to the e-Science Portal for New England Librarians, the two main branches of astronomy are optical and non-optical.
The e-Science Portal defines optical astronomy as the use of telescopes to study images and learn more about the universe. In non-optical astronomy, scientists use other tools and instruments to learn about the electromagnetic spectrum. For example, they use low-energy radio signals and high-energy gamma rays to learn more about neutron stars, black holes and many other topics.
Space.com explains the five subfields of astronomy. Planetary astronomy is the study of planets, stars and other non-Earthly bodies, and phenomena in and out of the solar system. Stellar astronomy explores how stars are created, how they evolve and how they die. Galactic astronomy is the study of the Milky Way, while extragalactic astronomy is the study of how galaxies beyond the Milky Way are grouped and interact. Cosmology is the study of the origin and development of the universe, and astronomy is closely related to the field of astrophysics and overlaps on many cosmology concepts. In fact, the two terms are often used interchangeably.