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Portal:Astronomy

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Introduction

A man sitting on a chair mounted to a moving platform, staring through a large telescope.
Percival Lowell observing Venus from the Lowell Observatory telescope in 1914

Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, 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 beyond Earth's atmosphere. Cosmology is a branch of astronomy that 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 Egyptians, Babylonians, Greeks, Indians, 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.

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.

Astronomy is one of the few sciences in which amateurs play an active role. 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. (Full article...)

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A model of the expanding universe opening up from the viewer's left, facing the viewer in a 3/4 pose.
Timeline of the expansion of the universe, where space, including hypothetical non-observable portions of the universe, is represented at each time by the circular sections. On the left, the dramatic expansion occurs in the inflationary epoch; and at the center, the expansion accelerates (artist's concept; neither time nor size are to scale).
The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. The notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations. The earliest empirical observation of the notion of an expanding universe is known as Hubble's law, published in work by physicist Edwin Hubble in 1929, which discerned that galaxies are moving away from Earth at a rate that accelerates proportionally with distance. Independent of Friedmann's work, and independent of Hubble's observations, physicist Georges Lemaître proposed that the universe emerged from a "primeval atom" in 1931, introducing the modern notion of the Big Bang.

Various cosmological models of the Big Bang explain the evolution of the observable universe from the earliest known periods through its subsequent large-scale form. These models offer a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure. The uniformity of the universe, known as the flatness problem, is explained through cosmic inflation: a sudden and very rapid expansion of space during the earliest moments. (Full article...)

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Credit: NASA

The International Space Station is photographed by an STS-134 crew member on the space shuttle Endeavour after the station and shuttle began their post-undocking relative separation. Undocking of the two spacecraft occurred on May 29, 2011.

Astronomy News

21 November 2024 –
The European Southern Observatory announces that its astronomers in Chile capture the first close-up image of a star outside the Milky Way. (The New York Times)
20 November 2024 – Discoveries of exoplanets
In a study published by the Nature journal, astronomers announce the discovery of IRAS 04125+2902 b, a newborn exoplanet. The discovery was made by Madyson Barber, a graduate student at the University of North Carolina at Chapel Hill. (Nature) (ABC News)
15 July 2024 – Mare Tranquillitatis pit
In the journal Nature Astronomy, American and Italian scientists announce the discovery of a lunar cave, approximately 250 miles (400 km) from the landing site of Apollo 11. (AP) (Nature Astronomy)

December anniversaries

  • 7 December 1972 – The Blue Marble photograph is taken by the Apollo 17 crew
  • 8 December 1992 – Galileo completes the second Earth flyby
  • 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
  • 17 December 1917 – 2001: A Space Odyssey science fiction author Arthur C. Clarke is born
  • 19 December 2013 – Gaia is launched for the mission to study billions of stars in the Milky Way
  • 21 December 1968 – Apollo 8, is launched with the first crewed spacecraft to leave Earth orbit, reach the Moon, orbit it, and return safely to Earth
  • 27 December 1571 – Astronomer, mathematician, and astrologer Johannes Kepler is born

Astronomical events

All times UT unless otherwise specified.

1 December, 06:21 New moon
6 December, 02:11 Mercury at inferior conjunction
7 December, 20:19 Jupiter at opposition
8 December, 08:56 Moon occults Saturn
9 December, 09:19 Moon occults Neptune
12 December, 13:18 Moon at perigee
14 December, 01:12 Geminids peak
15 December, 09:02 Full moon
18 December, 08:49 Moon occults Mars
21 December, 09:20 Earth southern solstice
22 December, 10:00 Ursids peak
24 December, 07:25 Moon at apogee
25 December, 01:59 Mercury at greatest western elongation
30 December, 22:27 New moon

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