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...)

Galileo image of 243 Ida. Pola Regio is located on the right "tip" of the asteroid. The dot to the right is its moon Dactyl.

243 Ida is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at Vienna Observatory and named after a nymph from Greek mythology. Later telescopic observations categorized Ida as an S-type asteroid, the most numerous type in the inner asteroid belt. On 28 August 1993, Ida was visited by the uncrewed Galileo spacecraft while en route to Jupiter. It was the second asteroid visited by a spacecraft and the first found to have a natural satellite.

Ida's orbit lies between the planets Mars and Jupiter, like all main-belt asteroids. Its orbital period is 4.84 years, and its rotation period is 4.63 hours. Ida has an average diameter of 31.4 km (19.5 mi). It is irregularly shaped and elongated, apparently composed of two large objects connected together. Its surface is one of the most heavily cratered in the Solar System, featuring a wide variety of crater sizes and ages. (Full article...)

• ... that Caroline Moore was 14 years old when she discovered supernova 2008ha?
• ... that although Charles Messier discovered the galaxy M91 in 1781, it was added to his catalogue only two centuries later?
• ... that the fall of the Neuschwanstein meteorite in 2002 was observed by the European Fireball Network and outdoor witnesses through most of Central Europe?
• ... that AG Pegasi has been described as the slowest nova ever recorded?

• ... that novelist Hal Clement created the planet Mesklin in 1953 based on the real-world suspected detection of an extrasolar planet?
• ... that the Passive Seismic Experiment Package recorded one of the first instances of humans littering on another planetary body?
• ... that the galaxy NGC 1700 has a rotating hot gas disk glowing in X-rays after merging with another galaxy three billion years ago?
• ... that Michael Collins has been called "one of the best clarinettists walking the planet" by The Times?
• ... that a profile of artist Mark Hearld said his "wrens and squirrels, field mice and owls" help a child care about the planet better than telling them it is burning?
• ... that a group of K-pop fans performed a dance with the goal of convincing a company to commit to 100% renewable energy?

NGC 4565 (also known as the Needle Galaxy or Caldwell 38) is an edge-on spiral galaxy about 30 to 50 million light-years away in the constellation Coma Berenices. The 10th magnitude galaxy sits perpendicular to our own Milky Way galaxy and is almost directly above the North Galactic Pole. First spotted in 1785 by Sir William Herschel (1738–1822), this is one of the most famous examples of an edge-on spiral galaxy.

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)

• 2 April 1968 – The epic science fiction film, 2001: A Space Odyssey is released
• 3 April 2014 – NASA announces that the Cassini orbiter has found evidence of an underground body of water on Enceladus, a moon of Saturn
• 7 April 2001 – Mars Odyssey orbiter is launched to map and search for water on Mars
• 12 April 1961 – Cosmonaut Yuri Gagarin becomes the first human to enter outer space when he is launched into orbital flight in Vostok 1
• 19 April 1971 – The first space station, Salyut 1, is launched into orbit
• 24 April 1990 – The Hubble Space Telescope, a powerful research tool and public relations boon for astronomy, is launched into orbit