The Astronomy Portal
Astronomy (from Greek: ἀστρονομία) is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates outside Earth's atmosphere. Cosmology is a branch of astronomy. It studies the Universe as a whole.
Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. Nowadays, professional astronomy is often said to be the same as astrophysics.
Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results.
Amateurs play an active role in astronomy. It is one of the few sciences in which this is the case. This is especially true for the discovery and observation of transient events. Amateur astronomers have helped with many important discoveries, such as finding new comets.
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A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus can be seen from Earth as a small black dot moving across the face of the Sun. The duration of such transits is usually several hours (the transit of 2012 lasted 6 hours and 40 minutes). A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than three times that of the Moon, Venus appears smaller, and travels more slowly across the face of the Sun, because it is much farther away from Earth.
Transits of Venus are among the rarest of predictable astronomical phenomena. They occur in a pattern that generally repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. The periodicity is a reflection of the fact that the orbital periods of Earth and Venus are close to 8:13 and 243:395 commensurabilities. Read more...
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Cassiopeia A (Cas A) is a supernova remnant in the constellation Cassiopeia and the brightest astronomical radio source in the sky, with a flux of 2720 Jy at 1 GHz. The supernova occurred approximately 11,000 light-years (3.4 kpc) away in the Milky Way.
- 14 December 1962 - Mariner 2 becomes the first space probe to perform a flyby of a planet, when it passes within 35,000 kilometers of Venus
- 19 December 2013 - Gaia was launched. Its mission is to study billions of stars in the Milky Way
- 21 December 1968 - Apollo 8, the first crewed spacecraft to leave Earth orbit, reach the Moon, orbit it, and return safely to Earth, is launched
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All times UT unless otherwise specified.
|5 December, 04:07
||Moon at apogee
|12 December, 05:12
|14 December, 16:00
|18 December, 20:27
||Moon at perigee
|22 December, 04:19
||Earth southern solstice
|26 December, 05:18
||New moon and annular solar eclipse
|26 December, 07:30
||Moon occults Jupiter
|27 December, 14:31
||Moon occults Pluto
|27 December, 18:25
||Jupiter at conjunction, occultation
|29 December, 01:31
||Moon occults Venus
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