Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry 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 the 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...)

Comet Shoemaker–Levy 9 (formally designated D/1993 F2) was a comet that broke apart in July 1992 and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of Solar System objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by astronomers worldwide. The collision provided new information about Jupiter and highlighted its possible role in reducing space debris in the inner Solar System.

The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker, and David Levy in 1993. Shoemaker–Levy 9 (SL9) had been captured by Jupiter and was orbiting the planet at the time. It was located on the night of March 24 in two photographs taken with the 46 cm (18 in) Schmidt telescope at the Palomar Observatory in California. It was the first active comet observed to be orbiting a planet, and had probably been captured by Jupiter around 20 to 30 years earlier. (Full article...)

• ... that the Lone Signal project sends messages by ordinary citizens to extraterrestrial civilizations using the Jamesburg Earth Station?
• ... that 6Q0B44E, a recently discovered satellite of Earth, is thought to be a large piece of space debris?
• ... that approximately one-third of nearby galaxies contain low-ionization nuclear emission-line regions?
• ... that lunar lava tubes could provide natural shelters for manned lunar habitats?
• ... that many geographic features on Campbell Island, New Zealand, were named for members of the French 1874 Transit of Venus astronomical expedition?

• ... that 1ES 1927+654, a galaxy in Draco, exhibited such extreme nuclear activity that it challenged conventional models of black-hole environments?
• ... that in many works of fiction, the asteroid belt is the remnants of a destroyed planet?
• ... that two competing hypotheses seek to explain the unusual orbit of the exoplanet Nu Octantis Ab?
• ... that Michael Collins has been called "one of the best clarinettists walking the planet" by The Times?
• ... that some exoplanets are evaporating catastrophically?
• ... that the active galaxy 3C 120 was given the variable-star designation BW Tauri because of its variability in the visible spectrum?

Hubble Space Telescope image of NGC 6052, discovered on 11 June 1784 by William Herschel. The two components of NGC 6052 are designated NGC 6052A and NGC 6052B are attracted by each other's gravity, have collided and are interacting with each other.

10 December 2025 – Brazil–China relations

Brazil and China begin constructing a joint laboratory for radio astronomic technology with the Federal University of Campina Grande and the Federal University of Paraíba to support space research as both countries work on the BINGO radio telescope. (Reuters)

• 1 January 1925 – Astronomer Edwin Hubble formally presents his discovery of galaxies outside the Milky Way at a meeting of the American Astronomical Society
• 1 January 1952 – The Kyiv Planetarium opens in Kyiv, Ukraine
• 3 January 1888 – The 91-centimeter refracting telescope at Lick Observatory, the world's largest telescope from 1888 to 1897, sees its first light
• 3 January 1999 – The Mars Polar Lander is launched by NASA to study the soil and climate of Planum Australe, a region near the south pole on Mars
• 4 January 2004 – The Mars rover Spirit lands, three weeks ahead of twin rover Opportunity, and begins exploring the Red Planet
• 14 January 2005 – The probe Huygens lands on Titan, a moon of Saturn, in the first successful landing in the outer Solar System
• 26 January 1949 – Hale Telescope, which introduced several innovations to telescope construction and was the world's largest telescope for nearly 30 years, has its first light