Space
Planets, moons, stars and galaxies, and the missions that went to see them.
Featured in Space
Start with these, then follow the links inside each article wherever they lead.
Solar System
The Solar System is the gravitationally bound system of the Sun and the masses that orbit it, most prominently its eight planets, of which Earth is one. The Solar System is an isolated single-star planetary system within the Milky Way Galaxy.
Sun
The Sun is the star located at the centre of the Solar System. It is a massive sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies.
Moon
The Moon is the only natural satellite of Earth. It orbits Earth at an average distance of 384,399 kilometers.
Mars
Mars is the fourth planet from the Sun. It is also known as the "Red Planet", for its orange-red appearance.
Jupiter
Jupiter is the fifth planet from the Sun, and the largest in the Solar System. It is a gas giant with a mass nearly 2.5 times that of all the other planets in the Solar System combined and slightly less than one-thousandth the mass of the Sun.
Saturn
Saturn is the sixth planet from the Sun, and is the second largest planet in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth.
Venus
Venus is the second planet from the Sun. Similar in size and mass to Earth, Venus has no liquid water, and its atmosphere is far thicker and denser than that of any other rocky body in the Solar System.
Mercury (planet)
Mercury is the first planet from the Sun and the smallest in the Solar System. It is a rocky planet with a trace atmosphere and a surface gravity slightly lower than that of Mars.
Uranus
Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant.
Neptune
Neptune is the eighth and farthest known planet orbiting the Sun. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet.
Pluto
Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun.
Milky Way
The Milky Way or Milky Way Galaxy, or simply the Galaxy, is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galaxy, which are so far away that they cannot be individually distinguished by the naked eye. The Milky Way is a barred spiral galaxy with a D25 isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs, but only about 1,000 light-years thick at the spiral arms (more at the bar).
Andromeda Galaxy
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224.
Galaxy
A galaxy is a physical system of stars, planetary systems, stellar remnants, substellar objects, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias, meaning 'milky', a reference to the Milky Way galaxy that contains the Solar System.
Star
A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun.
Supernova
A supernova is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion.
Neutron star
A neutron star is the gravitationally collapsed core of a massive supergiant star. It results from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.
Exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995.
Comet
A comet is an icy, small Solar System body or interstellar object that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma.
Asteroid
An asteroid is a minor planet, an object larger than a meteoroid that is neither a planet nor an identified comet, that orbits within the inner Solar System or is co-orbital with Jupiter (Trojan asteroids). Asteroids are rocky, metallic, or icy bodies with no atmosphere, and are broadly classified into C-type (carbonaceous), M-type (metallic), or S-type (silicaceous).
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versatile, renowned as a vital research tool and as a public relations boon for astronomy.
James Webb Space Telescope
The James Webb Space Telescope is a space telescope designed to conduct infrared astronomy. It is the largest telescope in space, and is equipped with high-resolution and high-sensitivity instruments, allowing it to view objects too old, distant, or faint for the Hubble Space Telescope.
Voyager 1
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 space beyond the Sun's heliosphere. It was launched 16 days after its twin, Voyager 2.
Sputnik 1
Sputnik 1, often referred to as simply Sputnik, was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program.
Yuri Gagarin
Yuri Alekseyevich Gagarin was a Soviet pilot and cosmonaut who became the first person to journey into outer space during the first successful crewed spaceflight. He was launched from the Baikonur Cosmodrome in the Kazakh SSR. Travelling on Vostok 1, Gagarin completed one orbit of Earth on 12 April 1961.
Apollo program
The Apollo program, also known as Project Apollo, was the United States human spaceflight program led by NASA, which landed the first humans on the Moon in 1969. Apollo was conceived in 1960 in the Dwight D. Eisenhower presidency during Project Mercury and executed after Project Gemini.
Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration as part of the Space Shuttle program. Its official program name was the Space Transportation System (STS), taken from the 1969 plan led by U.S. vice president Spiro Agnew for a system of reusable spacecraft where it was the only item funded for development.
Mars rover
A Mars rover is a remote-controlled motor vehicle designed to travel on the surface of Mars. Rovers have several advantages over stationary landers: they examine more territory, they can be directed to interesting features, they can place themselves in sunny positions to weather winter months, and they can advance the knowledge of how to perform very remote robotic vehicle control.
Dark matter
In astronomy and cosmology, dark matter is an invisible and hypothetical form of matter that does not interact with electromagnetic radiation, including light. Dark matter is implied by gravitational effects that cannot be explained by general relativity unless more matter is present than can be observed.
Dark energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on its largest scales. Its primary effect is to drive the accelerating expansion of the universe.
Cosmic microwave background
The cosmic microwave background, or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark.
Eclipse
An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy.
Aurora
An aurora is a natural light display in Earth's upper atmosphere caused by charged particles from the Sun colliding with atoms in the atmosphere.
Europa (moon)
Europa is the smallest and least massive of Jupiter's four Galilean moons. It is observable from Earth with common binoculars and is a planetary-mass moon, slightly smaller and less massive than Earth's Moon.
Titan (moon)
Titan is the largest moon of Saturn and the second largest in the Solar System. It is the only moon that is known to have a dense atmosphere, and is the only known object in the Solar System besides Earth with clear evidence of stable bodies of surface liquid.
Kuiper belt
The Kuiper belt is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger, 20 times as wide and 20-200 times as massive.
Guides in Space
A tour of the planets
From scorched Mercury to icy Neptune, what makes each of the eight planets distinct.
The Moon
How the Moon formed, why it has phases, what causes tides and eclipses, and what astronauts found there.
The history of space exploration
From the first rockets and Sputnik to the Moon landings, space stations and probes beyond the solar system.
Stars, galaxies and the universe
How astronomers measure the cosmos, what galaxies are, and the evidence that the universe began with the Big Bang.
Exoplanets and the search for life
How astronomers find planets around other stars, what they have found, and where life beyond Earth might exist.