Astronomer

An astronomer studies celestial objects, space, and the physical processes governing the universe, using observations, theory, or both.

Electromagnetic spectrum: The full range of electromagnetic radiation, ordered by wavelength or frequency. Astronomers study objects through radiation spanning radio waves to gamma rays.
Observational astronomy: The study of the universe through measurements of radiation and other signals from celestial objects. It is the branch in which astronomers directly gather evidence from the sky.
Hipparchus: An ancient Greek astronomer known for a star catalog and early systematic studies of celestial positions. His positional measurements helped establish astronomy as a quantitative science.
Astrology: A divinatory practice that interprets celestial positions as influencing human affairs and terrestrial events. It invokes celestial bodies, but its claims are not a scientific substitute for astronomy.
Telescope: An instrument that collects and focuses radiation to make distant objects easier to observe. Telescopes gather faint signals that astronomers use to measure the universe.
Theoretical astronomy: The use of mathematical models and physical theory to explain astronomical phenomena. It interprets observations and predicts behavior that instruments can test.
Nicolaus Copernicus: A Renaissance astronomer who formulated a heliocentric model placing the Sun near the center of planetary motion. His model challenged the Earth-centered framework used by earlier astronomers.
Astrophysics: The branch of astronomy that applies physics to explain the properties and behavior of celestial objects. The terms overlap substantially, though astrophysics emphasizes physical explanation.
Spectroscopy: The study of how matter interacts with radiation across different wavelengths. Spectra reveal celestial objects’ composition, temperature, motion, and physical conditions.
Radio astronomy: The study of celestial objects using radio-frequency radiation. Radio observations expose phenomena hidden from visible-light astronomy.

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