Portal:Astronomy

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The Astronomy Portal

Astronomy portal

A man sitting on a chair mounted to a moving platform, staring through a large telescope.

Astronomy (from Greek: ἀστρονομία) is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets; the phenomena include supernova explosions, gamma ray bursts, and cosmic microwave background radiation. More generally, all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole.

Astronomy is one of the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, Maya, and many ancient indigenous peoples of the Americas performed methodical observations of the night sky. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars, but professional astronomy is now often considered to be synonymous with astrophysics.

Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, which 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. The two fields complement each other, with theoretical astronomy seeking to explain observational results and observations being used to confirm theoretical results.

Astronomy is one of the few sciences in which amateurs still play an active role, especially in the discovery and observation of transient events. Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets.

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Ariel as seen by Voyager 2 in 1986. The canyon system Kachina Chasma stretches across the upper part of the image.
Ariel is the brightest and third most massive of the 27 known moons of Uranus. Discovered on 24 October 1851 by William Lassell, it is named for a sky spirit in Alexander Pope's The Rape of the Lock and Shakespeare's The Tempest. Like its parent planet, Ariel orbits on its side, giving it an extreme seasonal cycle. As of 2011, almost all knowledge of Ariel derives from a single flyby of Uranus performed by the spacecraft Voyager 2 in 1986, which managed to image 35% of the moon's surface. There are no plans at present to return to study the moon in more detail.

After Miranda, Ariel is the second-smallest of Uranus's five round satellites, and the second-closest to its planet. Among the smallest of the Solar System's 19 known spherical moons (it ranks 14th among them in diameter), Ariel is composed of roughly equal parts ice and rocky material. Like all of Uranus's moons, Ariel probably formed from an accretion disc that surrounded the planet shortly after its formation, and, like other large moons, it may be differentiated, with an inner core of rock surrounded by a mantle of ice. Ariel has a complex surface comprising extensive cratered terrain cross-cut by a system of scarps, canyons and ridges. The surface shows signs of more recent geological activity than other Uranian moons, most likely due to tidal heating.

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NGC 1300
Credit: NASA, ESA, and The Hubble Heritage Team STScI/AURA

NGC 1300 is a barred spiral galaxy about 61 million light-years away in the constellation Eridanus. The galaxy is about 110,000 light-years across; just slightly larger than our own galaxy, the Milky Way.

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These books may be in various stages of development. See also the related Science and Mathematics bookshelves.

  • Astronomy
  • GAT: A Glossary of Astronomical Terms
  • Introduction to Astrophysics
  • General relativity
  • Observing the Sky from 30°S
  • Observing the Sky from 40°N

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  • Solar System

Astronomical events

All times UT unless otherwise specified.

5 October, 22:18 Moon at perigee
9 October, 00:00 Draconids peak
9 October, 03:47 New moon
16 October, 07:16 Mars at southern solstice
17 October, 19:15 Moon at apogee
22 October, 08:00 Orionids peak
24 October Uranus at opposition
24 October, 16:45 Full moon
26 October, 14:18 Venus at inferior conjunction
31 October, 20:22 Moon at perigee

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