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...)

Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet, being orbital neighbours as well as Venus having the most similar mass and size to Earth among the planets of the Solar System. While both are rocky planets, Venus has an atmosphere much thicker and denser than Earth and any other rocky body in the Solar System. Its atmosphere is composed of mostly carbon dioxide (CO₂), with a global sulfuric acid cloud cover and no liquid water. At the mean surface level the atmosphere reaches a temperature of 737 K (464 °C; 867 °F) and a pressure 92 times greater than Earth's at sea level, turning the lowest layer of the carbon dioxide atmosphere into a supercritical fluid. Venus is the third brightest object in Earth's sky, after the Moon and the Sun, and, like Mercury, always appears relatively close to the Sun, either as a "morning star" or an "evening star", resulting from orbiting closer (inferior) to the Sun than Earth.

Venus is the destination from Earth, compared to the other planets, with the lowest delta-v needed to reach it, and is therefore often used for gravity assists and as a common waypoint for interplanetary flights from Earth. While the orbit of Venus is the next closest to Earth's, Venus and Earth stay on average the second closest planets to each other, with only the most inferior orbiting Mercury staying closer to them and all the other Solar System planets. Venus and Earth approach each other in synodic periods of 1.6 years. Venus has a very slow retrograde rotation about its axis, a result of competing forces of solar tidal locking and differential heating of Venus's massive atmosphere. A Venusian day is 116.75 Earth days long, about half a Venusian solar year, which is 224.7 Earth days long, and has no moons. (Full article...)

• ... that Abell 2142, a galaxy cluster, is one of the most massive objects in the universe?
• ... that a jet from one of the component stars of Z Canis Majoris is over 11 light-years long?
• ... that Messier 58 is one of the brightest galaxies in the Virgo Cluster and is 1 of 4 barred spiral galaxies included in Charles Messier's catalog?
• ... that the asteroid 2014 AA entered Earth's atmosphere on the early morning of January 2, 2014, less than a day after it was discovered?
• ... that ATIC, a balloon-borne detector flying over Antarctica, recently found excess cosmic ray electrons that might provide evidence for dark matter consisting of Kaluza-Klein particles?
• .... that the Sun fuses about 620 million metric tons of hydrogen per seconds due to Gravity?

• ... that the Passive Seismic Experiment Package recorded one of the first instances of humans littering on another planetary body?
• ... that Susan Murabana created Africa's first permanent planetarium?
• ... 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 the majority of extrasolar planets in fiction are inhabited by native species?
• ... that the active galaxy 3C 120 was given the variable-star designation BW Tauri because of its variability in the visible spectrum?
• ... that examples of artificial planets in science fiction include Riverworld, the Well World, and the Death Star?

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.

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)

• 1 May 1959 – The former Beltsville Center is renamed to Goddard Space Flight Center in honor of Dr. Robert H. Goddard, rocket pioneer who achieved first launch of a liquid-fueled rocket
• 4 May 1967 – Lunar Orbiter 4 is launched to perform a photographic survey of lunar surface features
• 7 May 1975 – Explorer 53 (SAS-C), a NASA X-ray astronomy space telescope, is launched from the San Marco Range in Kenya, Africa
• 7 May 1997 – English-language French science fiction action film, The Fifth Element is released showing passenger inter-constellation vehicles, spacefighter craft, and various non-human creatures
• 14 May 1935 – The planetarium at Griffith Observatory in Los Angeles, California opens
• 14 May 1973 – The first American space station, Skylab, is launched
• 18 May 1969 – The Apollo 10 human spaceflight is launched, testing all aspects of the lunar landing mission, except the actual lunar landing
• 20 May 1978 – Pioneer Venus is launched from Cape Canaveral, Florida becoming the first spacecraft placed in orbit around Venus
• 30 May 1971 – Mariner 9 robotic space probe is launched becoming the first spacecraft to orbit Mars