In contrast, 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 must observe snapshots of different systems at unique points in their evolution to determine how they form, evolve, and die.
On the other hand, theoretical astronomers construct and analyze models of entities that cannot be seen. Due to the fact that it takes millions to billions of years for a star system or a galaxy to go through its entire life cycle, astronomers must examine different systems at specific points in their evolution to learn how they are formed, change over time, and eventually end.