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The Astronomy Portal

Introduction

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...)

General images - load new batch

The following are images from various astronomy-related articles on Wikipedia.

Image 1The Hubble Space Telescope (from History of astronomy)
Image 2"El Caracol" observatory temple at Chichen Itza, Mexico (from History of astronomy)
Image 3The main platform at La Silla hosts a huge range of telescopes with which astronomers can explore the Universe. (from Observational astronomy)
Image 4Artist conception of the Big Bang cosmological model, the most widely accepted out of all in physical cosmology (neither time nor size to scale) (from Physical cosmology)
Image 5Segment of the astronomical ceiling of Senenmut's Tomb (circa 1479–1458 BCE), depicting constellations, protective deities, and twenty-four segmented wheels for the hours of the day and the months of the year (from History of astronomy)
Image 6An amateur astrophotography setup with an automated guide system connected to a laptop (from Observational astronomy)
Image 7The Nebra sky disk, Germany, 1800 - 1600 BC (from History of astronomy)
Image 8Map of the Milky Way Galaxy, with the constellations that cross the galactic plane in each direction and the known prominent components annotated including main arms, spurs, bar, nucleus/bulge, notable nebulae and globular clusters (from History of astronomy)
Image 9The Crab Nebula as seen in various wavelengths (from Observational astronomy)
$Image 1050 cm refracting telescope at Nice Observatory (from Observational astronomy)$

Image 1050 cm refracting telescope at Nice Observatory (from Observational astronomy)
Image 11History of the Universe – gravitational waves are hypothesized to arise from cosmic inflation, a rapidly accelerated expansion just after the Big Bang (from Physical cosmology)
Image 12Places like Paranal Observatory offer crystal clear skies for observing astronomical objects with or without instruments. (from Amateur astronomy)
Image 13Portrait of the Flemish astronomer Ferdinand Verbiest who became Head of the Mathematical Board and Director of the Observatory of the Chinese emperor in 1669 (from Astronomer)
Image 14Amateur astronomer recording observations of the sun. (from Amateur astronomy)
Image 15Sunset at the equinox from the prehistoric site of Pizzo Vento at Fondachelli Fantina, Sicily (from History of astronomy)
Image 16The Oort cloud, one of the most successful theoretical model about the Solar System (from Theoretical astronomy)
Image 17Historical Jantar Mantar observatory in Jaipur, India (from History of astronomy)
Image 18Southern Hemisphere (from History of astronomy)
Image 19Sir Patrick Moore was one of the world's leading popularisers of astronomy. (from Amateur astronomy)
Image 20An assembly in Estonia to observe meteors (from Observational astronomy)
Image 21Mayall telescope at Kitt Peak National Observatory (from Observational astronomy)
Image 22Arabic astrolabe from 1079 to 1080 AD (from History of astronomy)
Image 23One of the Oldest Observatories in South America is the Quito Astronomical Observatory, founded in 1873 and located 12 minutes south of the Equator in Quito, Ecuador. The Quito Astronomical Observatory is the National Observatory of Ecuador and is located in the Historic Center of Quito and is managed by the National Polytechnic School. (from Observational astronomy)
Image 24Historical accuracy of atomic clocks from NIST. (from Theoretical astronomy)
Image 25Comparison of CMB (Cosmic microwave background) results from satellites COBE, WMAP and Planck documenting a progress in 1989–2013 (from History of astronomy)
Image 26The Antikythera Mechanism was an analog computer from 150 to 100 BC designed to calculate the positions of astronomical objects. (from History of astronomy)
Image 279th-century diagram of the positions of the seven planets on 18 March 816, from the Leiden Aratea (from History of astronomy)
Image 28Overview of types of observational astronomy by observed wavelengths and their observability. (from Observational astronomy)
Image 29Calendrical functions of the Berlin Gold Hat c. 1000 BC (from History of astronomy)
Image 30The Northern Hemisphere page from Johann Bayer's 1661 edition of Uranometria - the first atlas to have star charts covering the entire celestial sphere (from History of astronomy)
Image 31An image of the Cat's Paw Nebula created combining the work of professional and amateur astronomers. The image is the combination of the 2.2-metre MPG/ESO telescope of the La Silla Observatory in Chile and a 0.4-meter amateur telescope. (from Amateur astronomy)
Image 32Babylonian tablet in the British Museum recording Halley's comet in 164 BC (from History of astronomy)
Image 33Ultra HD photography taken at La Silla Observatory (from Observational astronomy)
Image 34ALMA is the world's most powerful telescope for studying the Universe at submillimeter and millimeter wavelengths. (from Observational astronomy)
Image 35A voting session is conducted in 2006 International Astronomical Union's general assembly for determining a new definition of a planet (from Astronomer)
Image 36Amateur astronomy groups are often involved in outreach to introduce astronomy to the general public (from Amateur astronomy)

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This is a Featured article, which represents some of the best content on English Wikipedia.

General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations.

Newton's law of universal gravitation, which describes classical gravity, can be seen as a prediction of general relativity for the almost flat spacetime geometry around stationary mass distributions. Some predictions of general relativity, however, are beyond Newton's law of universal gravitation in classical physics. These predictions concern the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light, and include gravitational time dilation, gravitational lensing, the gravitational redshift of light, the Shapiro time delay and singularities/black holes. So far, all tests of general relativity have been shown to be in agreement with the theory. The time-dependent solutions of general relativity enable us to talk about the history of the universe and have provided the modern framework for cosmology, thus leading to the discovery of the Big Bang and cosmic microwave background radiation. Despite the introduction of a number of alternative theories, general relativity continues to be the simplest theory consistent with experimental data. (Full article...)

List of featured articles

Did you know - show different entries

... that light echoes appear to exceed the speed of light due to simple interstellar illusions?
... that the Leo IV dwarf galaxy is one of the smallest satellites of the Milky Way?
... that a hydrocarbon lake on Saturn's moon Titan and an active volcano on Jupiter's moon Io are among the Solar System features named after deities from Māori mythology?
... that the Local Void is an empty region of space, devoid of matter, lying adjacent to our own Milky Way galaxy?
... that William Herschel's 40-foot telescope was the largest telescope in the world for 50 years?

More Did you know facts

More Did you know (auto generated)

... that the Springfield Science Museum is home to the oldest operating projection planetarium in the United States?
... that Susan Murabana created Africa's first permanent planetarium?
... that examples of artificial planets in science fiction include Riverworld, the Well World, and the Death Star?
... that the active galaxy 3C 120 was given the variable-star designation BW Tauri because of its variability in the visible spectrum?
... that Michael Collins has been called "one of the best clarinettists walking the planet" by The Times?
... that King Gizzard & the Lizard Wizard's "cli-fi" thrash metal album addresses a mix of current ecological threats and attempts to find another planet to live on?

WikiProjects

WikiProject Astronomy	WikiProject Solar System



WikiProject Cosmology	WikiProject Spaceflight

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Credit: NASA / ESA

The stellar nursery LH 95, in the Large Magellanic Cloud. The Initial Mass Function of LH 95 does not seem to differ from that typical for the Milky Way galaxy. Image of the Large Magellanic Cloud, a dwarf galaxy. At a distance of 163,000 light-years, it is the third closest galaxy to the Milky Way.

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Astronomy 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)
20 February 2024 –: Astronomers identify the most luminous object ever observed, QSO J0529-4351, a quasar that accretes around one solar mass per day. (The Guardian) (Nature.com)

July anniversaries

1 July 2004 – The Cassini spacecraft arrives at Saturn after entering orbit
4 July 1997 – Mars Pathfinder and its rover, Sojourner, land on Mars, with the latter becoming the first rover to successfully travel the planet
5 July 1687 – Sir Isaac Newton's Philosophiæ Naturalis Principia Mathematica, which formulated the laws of motion and universal gravitation and applied them to celestial bodes, is first published
13 July 2007 – Gran Telescopio Canarias undergoes first light, becoming the largest telescope in the world
20 July 1969 – As part of the Apollo 11 mission, Americans Neil Armstrong and Buzz Aldrin become the first men to walk on the Moon
20 July 1976 – Viking 1 becomes the first spacecraft to successfully land on Mars and perform its mission
26 July 1971 – Apollo 15 launches with lunar rover payload

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Space-related Portals

Astronomical events

All times UT unless otherwise specified.

5 July, 05:59	Earth at aphelion
5 July, 22:57	New moon
12 July, 08:12	Moon at apogee
21 July, 10:17	Full moon
22 July, 06:59	Mercury at greatest eastern elongation
24 July, 05:43	Moon at perigee
24 July, 20:47	Moon occults Saturn
25 July, 15:01	Moon occults Neptune
27 July, 21:44	Southern Delta Aquariids peak