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Astronomy, science that encompasses the study of all extraterrestrial objects and phenomena. Since the late 19th century, astronomy has expanded to include astrophysics, the application of physical and chemical knowledge to an understanding of the nature of celestial objects.
Astronomy - Ancient Greece, Stars, Planets: Astronomy is present from the beginning of Greek literature. In Homer’s Iliad and Odyssey, stars and constellations are mentioned, including Orion, the Great Bear (Ursa Major), Boötes, Sirius, and the Pleiades.
Astronomy - Ancient, Celestial, Observations: Astronomy was the first natural science to reach a high level of sophistication and predictive ability, which it achieved already in the second half of the 1st millennium bce.
The study of astronomy involves all of the objects outside Earth’s atmosphere. These include the Sun, Moon, planets, stars, galaxies, and all other matter in the universe. People known as astronomers have studied these objects for thousands of years.
Unlike the observable universe, the universe is possibly infinite and without spatial edges. Zoom out from Earth's solar system to the Milky Way Galaxy, the Local Group, and beyond Scale of the universe. See all videos for this article.
Luminosity, in astronomy, the amount of light emitted by an object in a unit of time. The luminosity of the Sun is 3.846 × 1026 watts (or 3.846 × 1033 ergs per second). Luminosity is an absolute measure of radiant power; that is, its value is independent of an observer’s distance from an object.
ASTRONOMY meaning: the scientific study of stars, planets, and other objects in outer space.
A star is any massive self-luminous celestial body of derived from its internal energy sources. Of the tens of billions of trillions of stars in the observable universe, only a very small percentage are visible to the naked eye.
astrology, type of divination that involves the forecasting of earthly and human events through the observation and interpretation of the fixed stars, the Sun, the Moon, and the planets.
Geocentric model, any theory of the structure of the solar system (or the universe) in which Earth is assumed to be at the center of it all. The most highly developed geocentric model was that of Ptolemy of Alexandria (2nd century CE). It was generally accepted until the 16th century.