An astronomer is a scientist who studies celestial objects, such as stars, planets, moons, galaxies, and the universe as a whole. They seek to understand phenomena that occur beyond Earth's atmosphere, including the origins, evolution, and eventual fate of these celestial bodies and the universe itself. Astronomers use various methods and tools, including telescopes, satellites, and computer models, to collect data and analyze the properties and behaviors of astronomical objects.
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An astronomer investigates stars, planets, galaxies and other astronomical systems through observation and mathematical models. Telescopes collect signals, spectroscopy separates their wavelength components, and repeated measurements reveal changes over time.
The distinctive difficulty is that the object under study is usually inaccessible to a controlled laboratory intervention. An astronomer instead compares independent observables: stellar parallax constrains Euclidean distance, a radiation spectrum constrains physical conditions, and orbital motion constrains mass. Agreement among these measurements can test a model more strongly than fitting a single observable.
