Astronomy is the scientific study of celestial objects and phenomena that originate outside the Earth’s atmosphere. These objects and phenomena include the study of stars, planets, moons, comets, nebulae, galaxies, and cosmic background radiation. Astronomy is concerned with the physics, chemistry, meteorology, and motion of celestial objects as well as the universe as a whole, its formation, and development.
Astronomy is one of the oldest sciences, with early civilizations making astronomical observations. In 700 BC the Babylonians recorded and could predict future lunar eclipses. The invention of the telescope in 1608 transformed the world of astronomy. While early telescopes were primarily used for terrestrial observations, a small group of astronomers, including Galileo Galilei, began pointing them to the skies. The increased magnification of heavenly objects produced a significant and immediate impact with observations and interpretations of stars, the moon, Jupiter, the sun, and the phases of the planet Venus, transforming civilization's understanding of the universe.
Modern astronomy is split into two fields: observational and theoretical. Observational astronomy focuses on acquiring and analyzing data from celestial objects. Theoretical astronomy develops computer or analytical models describing astronomical objects and phenomena. The two fields complement one another, with theoretical astronomy seeking to explain observational data, and observational astronomy confirming theoretical results.
Astronomy is a natural science in which amateurs still play an active role, and amateur astronomers have contributed to many important astronomical discoveries.
Observational astronomy measures and records data from the observable universe. This means the electromagnetic radiation emitted from stars and other celestial objects as well as signals they produce such as neutrinos, and gravitational waves.
Observational astronomy using light utilizes optical telescopes (which come in two types: reflectors and refractors) to gather light and reveal more detail. Observational astronomy can be divided into fields based on the wavelength of light being measured including: radio, infrared (IR), ultraviolet (UV), x-ray, and gamma-ray telescopes.
Motivated by observational data, theoretical astronomers utilize numerical simulations to explain astronomical phenomena. Astronomical simulations and models help investigate phenomena in detail, examining ideas and viewpoints impossible to observe. Theoretical astronomy studies a wide range of objects including: moons, planets, stars, space plasma, galaxies, clusters of galaxies, active galactic nuclei, large-scale structures of the Universe, and the Universe itself.
Studies in astronomy can be divided into four subfields:
Astrophysics relates the principles of physics to astronomy to understand the physical processes of celestial bodies and the surrounding space. Astrophysics encapsulates the following subjects:
- Cosmology—How the universe was created and evolved.
- Spectroscopy—How light is reflected, absorbed, and transferred between matter
- Photometry—How luminous astronomical objects are based on electromagnetic radiation
- Heliophysics—The study of the sun
- Asteroseismology—Observations of stars to study their interior structure and dynamics
- Helioseismology—‚Asteroseismology specific to the sun.
Astrometry is the study of the position and motion of celestial bodies in space. It provides a frame of reference for the movement of celestial objects. Areas within astrometry include planetary science (planetology) and exoplanetology, the study of planets outside of our solar system.
Astrogeology studies the geology of celestial bodies such as planets, moons, asteroids, meteorites, and comets.
Astrobiology is a field looking for signs of life in the universe.
Astroseismology is a field which investigates the oscillations in stars in order to study their intentral structures.