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The Moon is the only natural satellite of Earth. It orbits around Earth at an average distance of 384,399 kilometres (238,854 mi), a distance roughly 30...

The European Space Agency (ESA), pronounced 'ee-sah', is a 23-member international organisation devoted to space exploration. It has its headquarters in...

The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological...

Voyager 1 is a space probe launched by NASA on September 5, 1977, as part of the Voyager program, to study the outer Solar System and the interstellar...

A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek...

The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south celestial latitude of the ecliptic – the apparent path of the...

Unsolved problem in physics What is dark matter? How was it generated? More unsolved problems in physics In astronomy and cosmology, dark matter is an...

A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal...

The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to...

An exoplanet or extrasolar planet is a planet outside of the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and...

Sirius is the brightest star in the night sky, located in the southern constellation of Canis Major. Its name is derived from the Greek word Σείριος (Latin...

Curiosity is a Mars rover that is exploring Gale crater and Mount Sharp on Mars as part of NASA's Mars Science Laboratory (MSL) mission. Launched in 2011...

A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including...

The Tunguska event was a large explosion of between 3 and 50 megatons TNT equivalent that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate...

Nine likeliest dwarf planets and dates of discovery A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough...

The Lunar Gateway is a cancelled program that planned to assemble a space station in orbit around the Moon as part of the Artemis program. One of the technical...

The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth; the electromagnetic radiation from...

The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to 149597870700 m. Historically, the astronomical unit was conceived...

Alpha Centauri (α Centauri, α Cen, or Alpha Cen) is a star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus...

In Big Bang models of physical cosmology, the age of the universe is the cosmological time back to the point when the scale factor of the universe extrapolates...