An astronomer is a scientist in the field of astronomy who concentrates their studies on a specific question or field outside of the scope of Earth. They look at stars, planets, moons, comets and galaxies, as well as many other celestial objects — either in observational astronomy, in analyzing the data or in theoretical astronomy. Examples of topics or fields astronomers work on include: planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. There are also related but distinct subjects like cosmology which studies the Universe as a whole. Astronomers usually fit into two types: Observational astronomers make direct observations of planets, stars and galaxies, and analyse the data. Theoretical astronomers create and investigate models of things that cannot be observed. Because it takes millions to billions of years for a system of stars or a galaxy to complete a life cycle astronomers have to observe snapshots of different systems at unique points in their evolution to determine how they form, evolve and die. They use this data to create models or simulations to theorize how different celestial bodies work. There are further subcategories inside these two main branches of astronomy such as planetary astronomy, galactic astronomy or cosmology.

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