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 is a natural science that is the study of celestial objects (such as moons, planets, stars, nebulae, and galaxies), the physics, chemistry, and evolution of such objects, and phenomena that originate outside the atmosphere of Earth, including supernovae explosions, gamma ray bursts, and cosmic background radiation.

Astronomy is one of the oldest sciences. Prehistoric cultures have left astronomical artifacts such as the Egyptian monuments and Nubian monuments, and early civilizations such as the Babylonians, Greeks, Chinese, Indians, Iranians and Maya performed methodical observations of the night sky. However, the invention of the telescope was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars, but professional astronomy is nowadays often considered to be synonymous with astrophysics.

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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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A color-composite image of the Pleiades from the Digitized Sky Survey
Credit: NASA/ESA/AURA/Caltech

In astronomy, the Pleiades, or Seven Sisters (Messier object 45), is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky.

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All times UT unless otherwise specified.

1 January, 20:00 Mercury at greatest western elongation
1 January, 21:55 Moon at perigee
2 January, 02:24 Full moon
3 January, 05:35 Earth at perihelion
3 January, 20:00 Quadrantids peak
9 January Pluto at conjunction
15 January, 02:24 Moon at apogee
17 January, 02:17 New moon
30 January, 10:04 Moon at perigee
31 January, 12:48 Ceres at opposition
31 January, 13:30 Full moon and total lunar eclipse

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