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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The Sun is the star at the center of the Solar System. It is a massive, hot ball of plasma, inflated and heated by energy produced by nuclear fusion reactions at its core. Part of this energy is emitted from its surface as visible light, ultraviolet, and infrared radiation, providing most of the energy for life on Earth. The Sun has been an object of veneration in many cultures. It has been a central subject for astronomical research since antiquity.

The Sun orbits the Galactic Center at a distance of 24,000 to 28,000 light-years. From Earth, it is on average 1 AU (1.496×10⁸ km) or about 8 light-minutes away. Its diameter is about 1,391,400 km (864,600 mi; 4.64 LS), 109 times that of Earth. Its mass is about 330,000 times that of Earth, making up about 99.86% of the total mass of the Solar System. Roughly three-quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron. (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 examples of artificial planets in science fiction include Riverworld, the Well World, and the Death Star?
• ... that Jessen's icosahedron has been used for both the "Skwish" children's toy and a NASA proposal for a "super ball bot" to cushion space landers on other planets?
• ... that the Passive Seismic Experiment Package recorded one of the first instances of humans littering on another planetary body?
• ... that in early depictions of Uranus in fiction, the planet was portrayed as solid
• ... that the star TRAPPIST-1 has seven planets, several of which may have temperatures that would allow the existence of liquid water (artist's impression depicted)?
• ... that it took five years of observations to find the planet orbiting the star HD 175167?

WikiProject Astronomy	WikiProject Solar System
WikiProject Cosmology	WikiProject Spaceflight

Credit: NASA, ESA, and The Hubble Heritage Team STScI/AURA

NGC 1300 is a barred spiral galaxy about 61 million light-years away in the constellation Eridanus. The galaxy is about 110,000 light-years across; just slightly larger than our own galaxy, the Milky Way.

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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)

24 November 2023 –

Astronomers at the Telescope Array Project in Utah, United States, observe the second largest cosmic ray ever detected, the so-called Amaterasu particle, with an energy of 244 EeV. (Cosmos Magazine)

• 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