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For your enjoyment and delight, we proudly present a list of space words and their definitions. And for extra convenience, they're even in alphabetical order! Pick a letter from our wonderful letter picker to begin.

Word	Meaning
A.S.I.	Agenzia Spaziele Italiana - The Italian Space Agency.
Abū Ishāq Ibrāhīm al-Zarqālī (Al-Zarqali / Arzachel)	A 11th-century Arab astronomer and mathematician who lived in what is now Spain. He made highly accurate calculations of the motions of the Sun, planets, and Moon. At the time, people believed Earth was the centre of the Solar System, but many of his measurements remained correct even after later astronomers confirmed that the Sun was at the centre. A lunar crater, Arzachel, is named in his honor.
Accretion	The build-up and accumulation of matter (dust and gas) which results in the formation of stars, planets, moons and other objects in solar systems.
Achernar	The brightest star in the constellation Eridanus and the ninth-brightest star in the night sky. Like Altair, it spins so fast that it is stretched out at the poles.
Acrux	The brightest star in the constellation Crux (the Southern Cross) and one of the brightest stars in the southern hemisphere. It is actually a system of multiple stars.
John Couch Adams	An English astronomer and mathematician (1819–1892) who was the first to predict the existence of Neptune using mathematics. In 1846, German astronomer Johann Galle discovered Neptune, but he used the predictions of French astronomer Urbain Le Verrier. Adams had made similar calculations earlier but did not publish them in time, so Le Verrier received most of the credit for the discovery.
Adrastea	Moon of Jupiter, discovered in 1979 by Voyager, 2nd closest moon to Jupiter, diameter 40 km (25 miles)
Aegir	A moon of Saturn, part of the Norse group of irregular moons. It has a retrograde orbit, meaning it moves in the opposite direction to Saturn’s rotation.
Aitne	Moon of Jupiter, discovered in 2003 by a group of astronomers at the University of Hawaii. It is irregularly shaped with a diameter of about 4 km (2 and a half miles). It orbits the planet at a distance of 23,981,000 km (14,901,100 miles).
Albedo	The measure of how much light a surface reflects. A high albedo means an object is very reflective (e.g. ice), while a low albedo means it absorbs more light (e.g. asphalt).
Albedo Feature	A bright or dark area on the surface of a planet, moon, or asteroid that reflects different amounts of sunlight. These features help scientists study the composition and history of celestial objects. For example, the dark patches on Mars show volcanic plains, while bright areas on the Moon are covered in reflective dust.
Albiorix	A moon of Saturn, the largest of the Gallic group of irregular moons. It has a reddish surface and may have originated from a larger body that broke apart.
Aldebaran	The brightest star in the constellation Taurus, often called the “Eye of the Bull.” It is an orange giant star and one of the brightest in the night sky.
Edwin "Buzz" Aldrin	Apollo 11 astronaut. Second man to walk on the Moon's surface.
Algenib	A bright star in the constellation Pegasus, part of the Great Square of Pegasus, a famous star pattern.
Alioth	The brightest star in the Big Dipper (part of the constellation Ursa Major) and the third-brightest star in the whole constellation.
Alkaid	The last and brightest star in the handle of the Big Dipper (Ursa Major).
Almach	A beautiful multiple star system in the constellation Andromeda. Through a telescope, it appears as a striking blue and orange pair.
Alpha Centauri	The closest star system to Earth after the Sun. It consists of three stars: Alpha Centauri A, Alpha Centauri B, and Proxima Centauri (which is actually the closest individual star). Alpha Centauri A and B form a binary system, while Proxima Centauri orbits them at a distance.
Altair	The brightest star in the constellation Aquila and one of the closest bright stars to Earth, about 16.7 light-years away. It spins very fast, making it more stretched at the poles than at the equator. Altair is part of the Summer Triangle, a group of three bright stars visible in the summer sky.
Amalthea	Moon of Jupiter, discovered in 1892 by Edward Emerson Barnard. 200 km (150 miles) in diameter.
Amino Acids in Space	Basic building blocks of life, found in comets and meteorites. These molecules are important because they suggest that the ingredients for life might exist beyond Earth and could have arrived on the planet from space.
Ananke	A retrograde moon of Jupiter, thought to be the largest remnant of a captured asteroid that broke apart due to Jupiter’s gravitational forces.
Andromeda	A large constellation best known for the Andromeda Galaxy (M31), the nearest major galaxy to the Milky Way.
Angular Momentum	The tendency of a spinning or orbiting object to keep moving in the same way unless something changes it. This is why planets stay in stable orbits around the Sun and why a spinning ice skater speeds up when they pull their arms in.
Anthe	A small moon of Saturn, discovered in 2007. It is embedded in the Anthe Ring Arc, a faint ring created by particles ejected from the moon itself.
Antimatter	The opposite of normal matter. When matter and antimatter collide, they annihilate each other, releasing energy.
Antlia	A faint constellation whose name means "the Air Pump."
Aoede	A small, irregular moon of Jupiter, part of the Pasiphae group. It has a highly inclined, retrograde orbit.
Apastron	The point at which a star in a binary system is farthest from its companion.
Aphelion	The point at which an object in orbit around the Sun is farthest from it. Opposite to perihelion.
Aphelion Precession	The slow movement of a planet's farthest point from the Sun due to gravitational forces.
Apoapsis	The point at which an object in orbit around any celestial body is farthest from that body. For example, a moon around Jupiter.
Apogee	The greatest distance of a body (the Moon or an artificial satellite) in its orbit around Earth.
Apogee Kick Motor (AKM)	A rocket motor used to adjust the orbit of satellites after launch.
Apollo (Space Program)	A series of U.S. space missions in the 1960s and 1970s designed to land astronauts on the Moon and return them safely to Earth. The program, run by NASA, included both unmanned and manned missions. Apollo 11 was the first successful Moon landing in 1969. Apollo 13's landing was aborted due to an explosion onboard, but the crew returned safely. The program ended with Apollo 17 in 1972.
Apollo Asteroids	A group of Earth-crossing asteroids named after 1862 Apollo, the first discovered of its kind.
Apollo Telescope Mount (ATM)	A solar observation module attached to Skylab, America’s first space station.
Apus	A small, faint constellation in the southern sky, named after a bird-of-paradise.
Aquarius	One of the zodiac constellations, representing the Water Bearer. It contains the famous Helix Nebula.
Aquila	A constellation in the northern sky, home to the bright star Altair.
Ara	A southern constellation whose name means "the Altar."
Dominique François JeanArago	French astronomer and physicist. He discovered the production of magnetism by rotation. He was also director of the Paris Observatory and lived from 1786 to 1853.
Arche	A tiny irregular moon of Jupiter, part of the Carme group, orbiting the planet in a distant, retrograde motion.
Arcturus	Arcturus is the brightest star in the constellation Boötes and the fourth brightest star in the night sky.
Arecibo Message	A powerful radio signal sent from Earth in 1974 to a star cluster called Messier 13, about 25,000 light-years away. It contained information about humans, our number system, DNA, and our solar system, designed as a message for potential extraterrestrial civilizations.
Ariel	One of the five major moons of Uranus, discovered in 1851. It has a bright, icy surface with canyons and fault lines, suggesting past geological activity.
Neil Armstrong	Apollo 11 astronaut. First man to walk on the Moon's surface.
Asteroid	Medium-sized rock fragments left over from the formation of the Solar System left to float around space. Smaller than planets but larger than meteoroids. Also known as "Planetoids"
Asteroid Belt	Region in between the orbits of Mars and Jupiter where a large number of asteroids orbit the Sun.
Asteroid Family	A group of asteroids that share similar orbits, likely originating from a single larger body.
Asteroid Number	Each asteroid discovered is given a number based on the order that it was discovered. 1 Ceres means that Ceres was the first asteroid to be discovered. 4 Vesta means that Vesta was the fourth asteroid to be discovered.
Astrobiology	The study of life in the universe. It looks at how life started on Earth, where life might exist on other planets or moons, and what kinds of living things could survive in space. Scientists search for clues in extreme places on Earth, like deep in the ocean or in deserts, to understand where life might exist beyond the planet.
Astrobiome	All the places beyond Earth where life could exist. This includes planets, moons, and even deep space environments where tiny life forms might survive in extreme conditions.
Astrochemistry	The study of chemical elements and molecules in space, including in stars and interstellar clouds.
Astrology	A belief system, not a science, that suggests the positions of celestial bodies influence people's lives.
Astronaut	A person who travels into space. Russia/Soviet equivalent is Cosmonaut.
Astronomical Unit	A unit of measurement used for measuring distances in space. 1 A.U. is equal to the approximate distance from the Earth to the Sun (150 million kilometres).
Astronomy	The study of the objects in the sky, eg: stars, planets, moons, galaxies, comets, asteroids, etc.
Astrophysics	The part of science that explains how space works. It uses ideas from physics to study things like stars, planets, black holes, and galaxies. Astrophysicists try to understand how these objects are made, how they move, and what forces (like gravity) affect them.
Atlas	A small moon of Saturn, shaped like a flying saucer due to an equatorial ridge formed by ring material. It orbits near the A ring.
Atmosphere	The layer of gas surrounding the surface of a planet, moon or star.
Atmospheric Drag	The resistance a satellite or space object experiences when moving through the outer layers of a planet’s atmosphere. In low Earth orbit (LEO), drag gradually slows satellites down, causing them to lose altitude and eventually re-enter the atmosphere. Space agencies must adjust satellite orbits to counteract this effect, or the objects will fall back to Earth and burn up.
Atom	A tiny particle of matter, itself made up of many particles of matter.
Aurora	Glowing lights in the sky caused by the interaction between the Solar Wind (charged particles from the Sun) and a planet's magnetic field.
Aurora Australis	An aurora which can be seen in the Southern Hemisphere. The glowing lights are caused by the interaction of charged particles from the Sun and Earth's magnetic field in the upper atmosphere (or ionosphere). Also known as the "Southern Lights"
Aurora Borealis	An aurora which can be seen in the Northern Hemisphere. The glowing lights are caused by the interaction of charged particles from the Sun and Earth's magnetic field in the upper atmosphere. Also known as the "Northern Lights"
Aurora Oval	The ring-shaped region around a planet’s magnetic poles where auroras are most commonly seen.
Autonoe	A tiny, distant moon of Jupiter, part of the Pasiphae group, with an irregular, retrograde orbit.
Axis	The imaginary line around which a planet, moon, star spins.
Azimuth	The direction of an object in the sky, measured in degrees from north (0°). For example, an object at 90° azimuth is directly east, while 180° is south. Azimuth is used in astronomy and navigation to help locate stars, planets, and satellites.
Heinrich Louis d'Arrest	Danish astronomer involved in the first observation of the planet Neptune. He was assisting German astronomer Galle who was using information provided by French mathematician Le Verrier about the position of an object beyond Uranus. While Galle observed the sky, d'Arrest read from a star chart. Galle spotted an object which wasn't listed on d'Arrest's chart, and the first observation of Neptune was made! D'Arrest lived from 1822 to 1875.

Word	Meaning
Edward Emerson Barnard	An American astronomer (1857–1923) who discovered Barnard’s Star, the fourth closest known star to Earth. He also discovered Amalthea, a moon of Jupiter, in 1892.
Barnard's Star	Fourth nearest star to Earth. 5.9 light years away.
Barnard’s Loop	A large red nebula in Orion, linked to past supernova explosions.
Barycentre (Barycenter)	The common centre of mass around which two or more celestial bodies orbit. For example, the Earth and Moon orbit a barycentre located just inside the Earth’s surface.
Bebhionn	A small moon of Saturn, discovered in 2004. It is part of the Gallic group of irregular moons, which have prograde orbits (moving in the same direction as Saturn's rotation). It is named after a figure from Irish mythology.
Belinda	A small moon of Uranus, approximately 80 km in diameter. It was discovered in 1986 by Voyager 2 and is the 10th closest moon to Uranus.
Bellatrix	A bright blue giant star in the Orion constellation. It is sometimes called the "Amazon Star" and is one of the hotter, more massive stars visible to the naked eye.
BepiColombo	A joint ESA (European Space Agency) and JAXA (Japan Aerospace Exploration Agency) mission launched in 2018 to study Mercury, the least explored planet in the inner Solar System. It consists of two orbiters that will map Mercury’s surface, study its magnetic field, and analyze its thin atmosphere once it arrives in 2025.
Bereshit (Beresheet)	An Israeli private lunar lander launched in 2019 by the company SpaceIL. It was part of an attempt to become the first privately funded mission to land on the Moon. However, the lander crashed due to a technical failure during descent.
Bergelmir	A small, irregular moon of Saturn, discovered in 2004. Part of the Norse group of moons.
Bestla	A small, irregular moon of Saturn, part of the Norse group of moons, discovered in 2004. It has a retrograde orbit, meaning it moves in the opposite direction to Saturn's rotation.
Beta Centauri	The second-brightest star in the Centaurus constellation, located near Alpha Centauri. It is actually a system of at least three stars and is much farther from Earth than Alpha Centauri.
Beta Lyrae	A famous binary star system where one star is being pulled apart by the other.
Betelgeuse	A bright red supergiant star in the constellation Orion, known for being one of the largest stars visible to the naked eye. It is expected to explode as a supernova sometime in the next 100,000 years.
Bianca	A small inner moon of Uranus, discovered by Voyager 2 in 1986. It is part of the Portia group of moons.
Big Bang	The event that marked the beginning of the universe around 13.8 billion years ago. Scientists believe the universe started as a tiny, incredibly hot and dense point, then expanded rapidly. This expansion continues today, causing galaxies to move farther apart.
Big Dipper	A well-known star pattern that is part of the larger constellation Ursa Major. It is often used to locate the North Star, Polaris.
Billion	In the U.S., a billion is one thousand million (1,000,000,000). In older British usage, a billion was one million million (1,000,000,000,000), but most scientists today use the American definition or scientific notation to avoid confusion.
Binary Star	A system of two stars that orbit a common center of mass. Many stars in the universe are part of binary or multiple star systems.
Bion Program	A series of Soviet and later Russian biological research missions launched between 1973 and 1996. The Bion satellites carried animals, plants, and microorganisms into space to study the effects of weightlessness on living organisms. These missions helped scientists understand how space travel affects life on Earth.
Biosignature	A chemical or physical feature that could indicate the presence of past or present life on another planet or moon.
Black Hole	A region of space where gravity is so strong that nothing, not even light, can escape. Black holes form when massive stars collapse under their own gravity at the end of their life cycle. They can be detected by their effect on nearby objects and radiation emitted from material falling into them.
Blazar	A type of extremely bright and active galactic nucleus, powered by a supermassive black hole.
Blueshift	When light from an object moving toward an observer appears to shift toward the blue end of the spectrum. This is the opposite of redshift, which happens when an object moves away.
Boötes Void	A vast, nearly empty region of space in the Boötes constellation. It is one of the largest known voids in the universe, with very few galaxies inside it. Sometimes called the "Great Nothing," it stretches about 330 million light-years across.
Johann Elert Bode	German astronomer, mostly known for "Bode's Law" (see below). Lived from 1747 to 1826.
Bode's Law	A mathematical formula designed by Johann Bode to predict the distances of planets from the Sun in astronomical units (A.U.). It accurately estimated the positions of planets up to Uranus and even hinted at the existence of the asteroid belt. However, it failed to predict Neptune’s orbit, suggesting that the pattern is more of a coincidence than a fundamental law of planetary formation.
Bok Globule	A small, dense cloud of gas and dust where stars may be forming. These dark patches are often seen in nebulae.
Bolide	An extra-bright meteor that becomes a fireball as it travels through the atmosphere, shining as bright or brighter than the light of a full moon. Geologists also refer to meteorites that have impacted a surface and form a crater as bolides.
Booster Rocket	A rocket used to provide extra thrust during the launch of a spacecraft. Many boosters, such as those on the Space Shuttle and Falcon Heavy, are jettisoned after use.
Bow Shock	The boundary where the solar wind (charged particles from the Sun) collides with a planet's magnetic field or an interstellar medium. For example, Earth's bow shock protects the planet by diverting harmful space radiation around it.
Brown Dwarf	A celestial object that is larger than a planet but too small to sustain nuclear fusion like a star. Often considered a "failed star."
Bubble Nebula	A nebula shaped like a bubble, located in the constellation Cassiopeia.
Bus Classification	A system used to classify asteroids based on the type of light they reflect (their spectral properties). It was developed by astronomer David Tholen in 1984 and later expanded by Richard P. Binzel in the 2000s. Asteroids are grouped into categories like C-type (carbon-rich), S-type (silicate or rocky), and X-type (metallic), helping scientists understand their composition and origins.

Word	Meaning
Caldera	A volcano that has sunk into the collapsed land below it (usually because all the magma below has erupted and there is nothing to support the newly formed mountain). Fairly common on Earth. An example elsewhere in the Solar System is Olympus Mons on Mars.
Caliban	An irregular moon of Uranus, named after a character in William Shakespeare’s play The Tempest.
Callirrhoe	A small moon of Jupiter, discovered in 1999. About 7 km in diameter, it follows a retrograde orbit, meaning it moves in the opposite direction to Jupiter's rotation.
Callisto	The second-largest moon of Jupiter and the third-largest moon in the Solar System. Callisto is about 99% the size of Mercury and is the most cratered body in the Solar System. It was discovered by Galileo in 1610.
Calypso	A small moon of Saturn, discovered in 1980. It shares its orbit with the larger moon Tethys and is part of Saturn’s Trojan moons.
Capella	The brightest star in the constellation Auriga and one of the closest giant stars to Earth.
Carme	Discovered in 1938, Carme became the eleventh moon known to orbit Jupiter. Irregularly shaped, about 48 km in diameter. The moon didn't receive its present name until 1975. Before then it was known as Jupiter XI, and between 1955 and 1975, some people knew it as Pan. Pan is now the name of a different moon that orbits Saturn, discovered in 1990.
Carpo	A small moon of Jupiter, discovered in 2003. It is only about 2 km in diameter and has a highly inclined orbit.
Catena	A chain of craters of similar size. They are believed to be created when an object like a comet is broken up into fragments and these fragments impact the surface of a planet or moon.
Celestial object	Any object which appears in the sky - the Moon, Sun, planets, stars, galaxies, etc. are all celestial objects.
Centaur (Astronomical Object)	A type of celestial object that shares characteristics of both asteroids and comets. Centaurs orbit between Jupiter and Neptune, with some showing comet-like activity.
Cepheid Variable	A type of star that changes in brightness over time. These stars are used as 'cosmic yardsticks' to measure distances in space.
Cetus	A large constellation named after a sea monster from Greek mythology. It contains several bright stars and galaxies.
Chaldene	Small moon of Jupiter, discovered in 2000, about 4 km in diameter.
Challenger (Space Shuttle)	A NASA space shuttle that tragically exploded 73 seconds after launch on January 28, 1986. It was the first space shuttle disaster and led to major changes in space safety protocols.
Chandrasekhar Limit	The maximum mass (about 1.4 times the Sun’s mass) that a white dwarf star can have before it collapses into a neutron star or black hole.
Chang’e Program	China’s lunar exploration program, named after the Chinese Moon goddess. It includes several successful robotic landers and sample return missions.
Chariklo	The largest known Centaur object, orbiting between Saturn and Uranus. It is the first minor planet discovered to have rings.
Charon	Moon of Pluto, discovered in 1978 and about one third the size of Pluto. Because Pluto and Charon orbit an invisible axis between the two objects, they are sometimes referred to as a Binary Planet.
James W. Christie	American astronomer who discovered Pluto's moon Charon in 1978. He was born in 1938.
Chromosphere	Part of the atmosphere of the Sun or any other star. It lies above a star's visible surface, its photosphere and below its outermost layer, its corona.
Churyumov–Gerasimenko	A comet visited by the ESA’s Rosetta spacecraft in 2014, famous for being the first comet where a lander (Philae) touched down.
Circumpolar Stars	Stars that never set below the horizon as seen from a particular location on Earth. These stars appear to move in circles around the celestial pole. In the Northern Hemisphere, an example is Polaris, the North Star.
Circumstellar Habitable Zone	Also called the Goldilocks Zone or Habitable Zone, this is a region around a star where temperatures and other conditions may be just right for any planets situated in them to be able to hold liquid water, greatly increasing the possibility of life existing on them. Earth is situated in the solar system's Habitable Zone.
Cluster	A group of stars or galaxies held together by gravity. There are two main types of star clusters: open clusters, which contain younger stars, and globular clusters, which are tightly packed groups of older stars.
Coma	The cloud of gas and dust surrounding the nucleus of a comet. It forms when the Sun’s heat causes the comet’s ice to vaporize, creating a glowing halo.
Comet	A small ball of ice, dust, and gas that orbits the Sun, often in an elliptical (oval) path. Comets become visible when they get close to the Sun, causing their ice to vaporize and form a glowing coma and tail. Some comets take decades to complete an orbit, while others take thousands of years.
Conjunction	A term used to describe the position of a planet relative to Earth and the Sun. An 'inferior conjunction' occurs when an inner planet (Mercury or Venus) is between Earth and the Sun. A 'superior conjunction' happens when the inner planet is on the opposite side of the Sun. A superior planet (Mars, Jupiter, etc.) is in conjunction when it is behind the Sun from Earth's perspective, and in 'opposition' when it is on the same side as Earth.
Constellation	A group of stars, named by ancient astronomers because of their appearance (kind of like dot-to-dot). The twelve signs of the zodiac are named after twelve constellations.
Cordelia	A small inner moon of Uranus, discovered by the Voyager 2 spacecraft in 1986. It is the innermost of Uranus’s moons and orbits just inside the planet’s bright epsilon ring, helping to keep the ring in place through its gravitational influence. Cordelia is named after the daughter of King Lear in Shakespeare’s play King Lear.
Corona	The outermost part of the atmosphere surrounding a celestial object like the Sun. Can often be seen during a solar eclipse. The corona extends many millions of kilometres into space. Lower in density than the rest of the star, not as bright (the Sun's disc has to be covered for it to be visible), but much hotter.
Cosmonaut	A person trained by Russia (or the former Soviet Union) to travel into space. The term is similar to "astronaut" but is specifically used for Russian space missions. The first person in space, Yuri Gagarin, was a cosmonaut, launching aboard Vostok 1 in 1961. Cosmonauts have been part of major space programs, including the Salyut, Mir, and International Space Station (ISS) missions.
Crater	A bowl-shaped depression formed when a meteorite hits the surface of a planet or moon.
Cressida	A small inner moon of Uranus, discovered by Voyager 2 in 1986. It is part of a group of moons that orbit close to Uranus and may eventually collide with another moon or break apart due to gravitational forces. It is about 80 km in diameter and named after a character in Shakespeare’s play Troilus and Cressida.
Crust	The outermost solid layer of a planet, moon, or other rocky body. It is made of rock and minerals and is much thinner than the layers beneath it, such as the mantle and core. On Earth, the crust is where land, oceans, and all known life exist. Other planets and moons also have crusts, though they may be thicker, thinner, or made of different materials, depending on their composition and history.
Cupid	Moon of Uranus with a diameter of 18km (11 miles). Discovered in 2003 by Mark Robert Showalter and Jonathan Lissauer. Named after a character in William Shakespeare's play Timon of Athens

Word	Meaning
Daphnis	Moon of Saturn, discovered on 1st May 2005 from images taken by the Cassini spacecraft. Its diameter is about 8 kilometres (5 miles). It orbits within Saturn's A Ring. It gets its name from Daphnis, a Sicilian shepherd and poet in Greek mythology.
Dark Dust Cloud	A cloud of dust which doesn't let light through! It is usually area in space which contains a concentration of gas and dust. As it prevents light from penetrating it, it means that stars behind it are not visible.
Dark Matter	Most of space is "dark matter"! It is matter (particles of gas and dust) that is too dim to be picked up by telescopes, but astronomers know it's there by the influence of its gravity (recognised by the effect it has on other objects).
Day	Length of time it takes for a planet to completely rotate on its axis, most often in reference to the length of time it takes for Earth to complete a rotation. A "day" on Mars often referred to as a "Sol".
Deep Ecliptic Survey (DES)	A project to detect and discover Kuiper Belt objects beyond the orbit of Neptune. It ran from 1998 to 2005, discovering 663 objects of interest over 125 nights. Observations were made through the Kitt Peak or Cerro Tololo telescopes. Some attempts to make observations were hampered by bad weather. Further info is available here
Deimos	One of two of Mars' moons (Phobos is the other). Both moons are irregularly shaped with Deimos being the most distant and the smaller of the two moons, orbiting at 23,460 kilometres (15,577 miles) away from the planet and at a size of 16 km by 12 km (10 miles by 7.5 miles). Deimos was discovered on 12th August 1877 by American astronomy Asaph Hall Senior. He also discovered Phobos on the same date. Deimos takes 30.4 hours to orbit Mars.
Density	A measure of how closely packed matter is. Gas is less dense (less compact) than water. Water is less dense than a solid.
Desdemona	Moon of Uranus, discovered by Voyager 2 in 1986. Named after the heroine in WIlliam Shakepeare's play Othello
Despina	Moon of Neptune, third closest to the planet. Its diameter is 152 kilometres (94 miles) and it orbits at 52,526 km (32,638 miles) from Neptune. Despina was discovered in 1989 by the Voyager 2 space craft.
Diameter	The distance from one side of a round object to the opposite side going through its centre. In astronomy, this usually refers to the width of a planet, moon or star. Some of these objects are not completely spherical (like Jupiter) so the diameter is wider than the distance from top to bottom.
Dione	Moon of Saturn
Double Planet	Two planets which are attracted to each other by their respective gravitational pulls. They orbit around a point in between each other (but not necessarily exactly in the middle of each other). An example of this in the Solar System may be Pluto and Charon and some think even Earth and the Moon. Also referred to as a Binary Planet.
Double Star	Two stars that are attracted to each other by their respective gravitational pulls. They orbit around a point in between each other. Also known as Binary Star

Word	Meaning
Earth	The third planet from the Sun and the fifth largest planet in the Solar System. The only planet in the Solar System where large quantities of water exist, and the only planet in the Universe on which life is known to exist. Earth has one natural satellite (the Moon).
EDT	Eastern Daylight Time. The time used during Spring and Summer on the East Coast in the United States , the west coast in South America, the Bahamas and some Caribbean islands. The time is four hours behind GMT (Greenwich Mean Time) or UTC (Universal Time Coordinate). As Eastern Daylight Time is used in Florida, it is sometimes used when describing the times of space launches from Kennedy Space Center in Florida.
Elara
Element	Chemical material in its simplest form, such as hydrogen, helium, oxygen, carbon, etc. An element can be a solid, a liquid or a gas. Matter is made up of many elements. There are 105 elements in total. The Solar System was formed out of a cloud of matter. The elements in this matter combined with other elements as they formed the Sun and planets. For example, when carbon combined with oxygen, it formed carbon dioxide.
Elliptical/Ellipse	An elongated circle. Most of the planets in the Solar System don't orbit in perfect circles; instead their orbits are elliptical, meaning that they may be oval shaped and sometimes the Sun isn't exactly central. Venus has the most circular orbit, whereas dwarf planets like Pluto and Eris are the most eliptical.
Enceladus
Epimetheus	moon of saturn
Erinome	moon of jupiter
Erriapus	moon of saturn
ESA	European Space Agency. A group of 22 European countries which design, develop and launch satellites and probes into space. ESA's most notable missions are Mars Express and Venus Express. The nations which make up the ESA are Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Luxembourg, the Netherlands, Norway, Poland, Portugal, Romania, Spain, Sweden, Switzerland and the United Kingdom.
Escape Velocity	The minimum velocity (or speed) that an object needs to be travelling at to escape the gravitational pull of a much larger object. For example, for a rocket to leave the orbit of Earth, it needs to reach a certain velocity or else it will fall back to Earth. On planets and moons with a smaller pull of gravity (the Moon, Mars), the velocity needed to leave that object would be much less.
EST	Eastern Standard Time. The time used during Autumn/Fall and Winter on the East Coast of North America, the west coast in South America, the Bahamas and some Caribbean islands. The time is five hours behind GMT (Greenwich Mean Time) and UTC (Universal Time Coordinate). As Florida falls under Eastern Standard Time, many launches from Kennedy Space Center are referred to under the EST time.
Euanthe	moon of jupiter
Eukelade	moon of jupiter
Europa	moon of jupiter
Eurydome	moon of jupiter
Event Horizon	The boundary of a black hole. The pull of gravity beyond this point is so great that for any matter to escape it, it must be travelling faster than the speed of light.
Exoplanet/Extrasolar Planet	A planet which orbits another star in the Universe. By June 2007, there were 242 planets known to orbit other stars. Most exoplanets are detected by the effect they have on their host stars and haven't actually been imaged. Most known exoplanets are more like Jupiter than Earth (since a planet like Earth won't have a very visible effect on its host star so isn't known about). Although few Earth-like planets are known to exist, it is certain that several of them do exist which greatly increases the chances of life existing or being able to exist elsewhere in the Universe.
Extra Terrestrial	Literally means "not of" or "beyond the Earth". Refers to anything that doesn't belong to planet Earth. An Extra Terrestrial would be a being from another planet, or an alien.

Word	Meaning
Farbauti	moon of saturn
Fenrir	moon of saturn
Ferdinand	moon of uranus
Field of View	The area of sky that can be seen through a telescope.
Field Star (or Field Galaxy)	A star (or galaxy) which is in the area being viewed by an astronomer but is not the object that they are actually looking at.
Filter	Filters can be used to absorb certain colours or an amount of light to allow an object to be viewed more clearly. For example, filtering out a prominent colour while observing a planet makes it easier to view details of other colours. Observing the Sun through filters allows sunspots to be seen as a decreased amount of sunlight can pass through the filter.
Flare	A sudden burst of energy from a star, like the Sun.These usually occur on the Sun around sunspots. The energy is released from the Sun as flares which can extend many millions of miles from the Sun, emitting radiation and particles. If they reach Earth, they can cause radio interference. Solar flares can often be seen during eclipses or if the Sun is being observed through a telescope with a disc placed on the lens to block out the Sun's disc.
Flat Earth Society	Society originally based in England but now in California which believes that Earth is flat, despite overwhelming scientific evidence proving otherwise.
Flyby	Mission involving a spacecraft flying past an object (planet, moon, comet, asteroid) to take pictures and make observations of it. They were fairly common in the early years of space exploration before scientists were able to get crafts to land on objects or place them into orbits. They are also used if a spacecraft passes by an object of interest en route to another destination or is visiting multiple destinations as part of its mission (for example, Voyager 2 flew by the four Gas Giants and sent back images of all of them and some of their moons).
Flymo	A lawnmower
Fornjot	moon of saturn
Francisco	moon of uranus

Word	Meaning
Galactic Centre	The nucleus, or centre, of a galaxy, usually densely populated by stars. The galactic centre of the Milky Way is about 28,000 light years from Earth.
Galatea	Moon of Neptune, fourth closest to the planet. Galatea is 175 kilometres (109 miles) in diameter and orbits Neptune at an average distance of 61,953 km (38,496 miles). It was discovered by Voyager 2 in 1989.
Galaxy	A large group of stars, bound together by gravity. Quite often, the galaxy will form a spiral or circular shape.
Galilean Satellites / Galilean Moons	Jupiter's four largest moons, discovered by Galileo in 1610. These are (in order of increasing distance from Jupiter) Io, Europa, Ganymede and Calisto. Ganymede is the largest moon in the Solar System.
Galle, Johann Gottfried	German astronomer who made the first observation of Neptune, assisted by Heinrich Louis d'Arret. This observation was based on predictions of the planet's position by French mathematician Le Verrier.
Gamma Rays	A form of energy such as light, but made from shorter and more powerful waves.
Ganymede	Moon of Jupiter, largest moon in the Solar System. Ganymede's surface is more heavily cratered on one side than the other. It is about 5,262 km in diameter (a greater diameter than both Mercury and Pluto) and takes 7 days and 3 hours to complete an orbit of Jupiter.
Gas Giant	A planet with a small, possibly rocky core, surrounded by a deep atmosphere. This atmosphere is made up mainly of hydrogen and helium gases. There are four Gas Giants in your Solar System. These are Jupiter, Saturn, Uranus and Neptune. The majority of planets so far discovered around other stars are also Gas Giants, but that's likely to be because they're larger and easier to spot.
Geostationary / Geosynchronous Orbit	An orbit of a satellite around Earth which is in a stationary position above a set point on Earth, taking the same length of time to orbit Earth as it takes for Earth to spin on its axis (24 hours). Communications satellites (for example, those used to broadcast satellite television) and weather satellites are most commonly placed into geostationary orbits.
Goldilocks Zone	A region in the orbit of a star where bears live in cottages and eat porridge for breakfast. Ignore the stuff about bears, although it does get its name from the children's story! It's actually a zone where any objects located in it may be habitable. Temperatures in the Goldilocks Zone are just right (not too hot or too cold) so any water there can exist as a liquid. Earth is situated in the Goldilocks Zone in the solar system. It can also be called the habitable zone or circumstellar habitable zone. Other stars will have Goldilocks Zones so planets discovered in them would be of great interest to scientists.
Gravity	A force which attracts objects of mass to objects of a greater mass. This force is what created the stars and planets, and keeps people stuck to Earth. The more massive an object, the stronger its gravitational force. The Sun's gravity is able to keep planets many millions of miles away from it in orbit around it.
Gravity Assist	A method used to propel a spacecraft to a planet or moon using the gravity of another planet or moon. This is done by the object entering into the orbit of a planet, therefore now travelling around the Sun at the same speed as the planet. It then gets slung out of this orbit and uses the velocity it has built up to travel faster to its next destination. The first mission to use this was Mariner 10 which used the gravity of Venus to take it to Mercury. The most famous mission to use gravity assist was the Voyager which used the gravity of the four Gas Giants to propel the craft to each planet and now on their ways out of the Solar System.
Greip	moon of saturn

Word	Meaning
Habitable Zone	Also called the Goldilocks Zone or Circumstellar Habitable Zone, this is a region around a star where temperatures and other conditions may be just right for any planets situated in them to be able to hold liquid water, greatly increasing the possibility of life existing on them. Earth is situated in the solar system's Habitable Zone.
Halimede	Moon of Neptune. Halimede was discovered in 2002 by a team of astronomers headed by Matthew J Holman. It is the fifth most distant moon of Neptune, only 60 kilometres (37 miles) in diameter and orbiting at 15,728,000 km (9,772,926 miles) from the planet.
Harpalyke	moon of jupiter
Hati
Heat Shield	A protective covering of a spacecraft which protects the craft and its crew from the intense heat caused by friction as the spacecraft re-enters Earth's atmosphere. The heat shield of the Space Shuttle is made up of many heat resistant tiles.
Hegemone	moon of jupiter
Helike	moon of jupiter
Heliocentric	With the Sun at the centre. The solar system is heliocentric as the Sun is at the centre of it and all of the objects orbit it. A planet like Earth is in a heliocentric orbit. Moons orbit planets so are not in heliocentric orbits.
Helium	The second most common element in the universe after hydrogen. The atmosphere of large gas planets like Jupiter and Saturn is made up of hydrogen and helium. Stars turn their supply of hydrogen into helium, created the light and heat that is necessary for life on planets like Earth..
Hermippe	moon of jupiter
Himalia	moon of jupiter
Hippocamp	Smallest moon of Neptune. It is an inner moon with a diameter of 34 km (21 miles). It orbits at an average distance of 105,300 km (65,433 miles) from Neptune, taking 23 hours to complete an orbit. It was discovered in 2013 from photos taken between 2004 and 2009.
Hydrogen	The most common element in the universe and also the simplest. Stars in their early life are made up almost entirely of hydrogen. By converting this hydrogen into helium, through a process called binary fission, they produce heat and light.
Hyrrokkin

Word	Meaning
Iapetus	moon of saturn
Ijiraq	moon of saturn
Infrared	Invisible rays. They cannot be seen as the waves that produce them are longer than the waves at the red end of a rainbow. They can be felt though, usually as heat.
Inner Planets	Mercury, Venus, Earth and Mars. These are the four planets closest to the Sun. They are the four smallest planets and all have solid surfaces. They are sometimes called the Terrestrial Planets. The inner planets are separated from the outer planets by the Asteroid Belt.
Io	moon of jupiter
Iocaste	moon of jupiter
Isonoe	moon of jupiter

Word	Meaning

Word	Meaning
Kale	moon of jupiter
Kallichore	moon of jupiter
Kalyke	moon of jupiter
Kari
Kiviuq	moon of saturn
Kore	moon of jupiter

Word	Meaning
Lander
Laomedeia	Moon of Neptune discovered in 2002. It has a diameter of 42km (26 miles) and takes 3168 days to orbit Neptune at an average distance of 23.5 million km (14.6 million miles). It is named after the Greek Nereid "folk leader"
Larissa	Fourth largest moon of Neptune with a diameter of 194 km (121 miles). It orbits the planet in 13 hours from an average distance of 73,548 km (45,703 miles). It was located in 1981 but first imaged in 1989 by Voyager 2.
Leda
Light
Light year
Loge
Lysithea

Word	Meaning
"M" numbers
Magnetic Field
Magnitude
Mantle
Margaret
Mars
Mass
Matter
Megaclite	moon of jupiter
Mercury
Meteor
Meteorite
Methone	moon of saturn
Metis	moon of jupiter
Mimas	moon of saturn
Miranda
Mneme	moon of jupiter
Moon
Mundilfari	moon of saturn

Word	Meaning
Naiad	Neptune's closest moon, discovered in 1989 by Voyager 2. It orbits Neptune at a distance of 48,227 kilometres (29,967 miles) and is just 67 km (42 miles) in diameter.
Narvi	moon of saturn
Nebula (plural nebulae)
Nereid	Neptune's third largest moon and the second to be discovered orbiting the planet. It was found by Dutch-American astronomer, Gerard P. Kuiper, in 1949. It is the sixth most distant moon of Neptune, orbiting at an average distance of 5,513,400 kilometres (3,425,868 miles) from the planet. It is about 340 kilometres (211 miles) in diameter.
Neso	Most distant of Neptune's moons, discovered in 2003 by Matthew J Holman and Brett J Gladman. Orbiting at a distance of 48,387,000 kilometres (30,066,288 miles), Neso is the most distant known moon of any planet in the Solar System. Neso has a diameter of approximately 60 km (37 miles)
Neutron Star
Nuclear Energy
Nuclear Fusion
Nucleus (plural nuclei)

Word	Meaning
Observatory
Ophelia	moon of uranus
Orbit
Orbiter
Orthosie	moon of jupiter
Outer Planets	Jupiter, Saturn, Uranus and Neptune. These are the four planets most distant from the Sun. They are the largest planets in the solar system and are made up mostly of gas although may have small solid or liquid metallic cores. They are also referred to as the gas giants.

Word	Meaning
Paaliaq	moon of saturn
Pallene	moon of saturn
Pan	moon of saturn
Pandora	moon of saturn
Particle
Pasiphae	moon of jupiter
Pasithee	moon of jupiter
Perdita
Perihelion	The closest distance that an object like a planet, asteroid or comet gets to the Sun while orbiting it. Most objects in the solar system orbit in eccentic orbits, so there is a difference between their closest point to the Sun and their furthest point. Earth for example gets as close as 147 million kilometres to the Sun. This is its perihelion. An object's most distant distance from the Sun is called its aphelion. Earth's aphelion is around 152 million kilometres.
Periodic Comet
Phobos	moon of mars
Phoebe	moon of saturn
Photosphere
Planet	Spherical object which orbits a star. Planets can vary greatly in size although are never larger than the star they orbit. Planets can be rocky or gaseous. Smaller planets tend to have solid surfaces whereas larger planets are balls of mostly gas. There are eight planets known to orbit the Sun and at least 270 planets known to orbit other stars (these planets are known as extrasolar planets or exoplanets).
Planetary Nebula
Pluto	Tiny world orbiting the Sun in a very elliptical orbit, going as close as 4,443,000,000 km from the Sun to as far as 7,682,900,000 km away from it. Regarded as the ninth planet in the Solar System since its discovery in 1930 until being reclassified as a Dwarf Planet in 2006. Pluto takes 248 years to complete an orbit around the Sun. With a diameter of 2,280 km, Pluto is smaller than Earth's moon. Orbiting Pluto are 3 known moons: Charon, Hydra and Nix.
Poles
Polydeuces	moon of saturn
Portia
Praxidike
Prometheus	moon of saturn
Prospero
Proteus	Neptune's second largest moon. In was discovered in July 1989 by Voyager 2. Its diameter is about 420 km (261 miles) and it takes 27 hours to orbit Neptune. It is situated about 117,647 km (73,106 miles) from Neptune
Psamathe	Moon of Neptune, discovered in 2003. It has a diameter of 38 km (24 miles) and orbits at an average distance of 46.7 million km (29 million miles). One orbit takes 9,117 days. It is named after a Nereid, a sea nymph. Psamathe in mythology was the goddess of sand.
Puck

Word	Meaning
Quaoar	Small Kuiper Belt object, potential Dwarf Planet.

Word	Meaning
Radiation
Radio Waves
Re-entry
Rhea	moon of saturn
Rosalind

Word	Meaning
Sao	Moon of Neptune, discovered in 2002. It has a diameter of 44 km (27 miles) and orbits at a distance of 22.4 million km (13.9 million miles) from Neptune, taking 2,914 days to complete an orbit. It is named after a Nereid, a sea nymph in Greek mythology. Sao helped sailors to navigate stormy seas safely, or rescue those that weren't so lucky.
Satellite
Saturn
Schirra, Walter	Apollo 9, Apollo 15 astronaut
Scott, David	Apollo 7 astronaut.
Sedna
Setebos
Shooting Star
Siarnaq	moon of saturn
Sinope	moon of neptune
Skathi	moon of saturn
Skoll	moon of saturn
Solar Eclipse
Solar Flare
Solar System	The name given to the Sun and its family of planets and dwarf planets (plus their moons), comets and asteroids. The Sun is at the centre of the Solar System with all of the other objects held in orbit of it by the Sun's gravitational pull. Earth is one of the planets in the Solar System, and the only one known to have life. The Solar System is considered to end when the Sun's gravity no longer has an effect. Other stars also have objects like planets and comets orbiting them, so can also be considered to be solar systems.
Solar Wind
Space
Space Craft / Space Probe
Spacewalk
Spicule
Sponde	moon of neptune
Star	A ball of gas,
Stephano
Sun
Sun Spot
Supernova
Surtur	moon of saturn
Suttungr	moon of saturn
Sycorax

Word	Meaning
Tarqeq	moon of saturn
Tarvos	moon of saturn
Taygete	moon of jupiter
Telescope	Instrument (not a musical one) that is used to see deeper into space and look closer at objects. Considered to have been invented in the Netherlands in 1608, telescopes make use of mirrors and shaped lenses to magnify the view of the viewed subject. Early discoveries that were possible because of the invention of the telescope were the moons of Jupiter and the rings of Saturn, all observed for the first time by Galilei Galileo in 1610. Telescopes in space like the Hubble Space Telescope and James Webb Telescope benefit from being able to make clearer observations as they don't have to look through Earth's atmophere.
Telesto	moon of saturn
Terrestrial Planets	Mercury, Venus, Earth and Mars. These are the four planets closest to the Sun. They are the four smallest planets and all have solid surfaces. They are more commonly referred to as the inner planets. They are separated from the outer planets by the Asteroid Belt.
Tethys	moon of saturn
Thalassa	Second closest moon of Neptune, orbiting the planet at an average distance of 50,075 kilometres (31,115 miles). Its diameter is about 83 km (52 miles). Thalassa was discovered in 1989 by Voyager 2.
Thebe	moon of jupiter
Thelxinoe	moon of jupiter
Themisto	moon of jupiter
Thrust
Thruster
Thrymr	moon of saturn
Thyone	moon of jupiter
Titan	moon of saturn
Titania
Trinculo
Triton	Neptune's largest moon. It was discovered in 1846 by British astronomer and beer brewer, William Lassell, and thought to be Neptune's only moon until Nereid was discovered in 1949. Triton is Neptune's only spherical moon with a diameter of 2,707 kilometres. It orbits at a distance of 354,800 kilometres (220,462 miles) taking 5 days and 21 hours to complete an orbit.

Word	Meaning
Ultraviolet
Umbriel
Uranus

Word	Meaning
Venus	Second planet from the Sun, slightly smaller than Earth. Venus has a thick poisonous atmosphere and a surface covered in ancient volcanoes. Temperatures at Venus' surface are the hottest of any of the planets in the Solar System, even hotter than Mercury which is closer to the Sun. Venus has no moons.

Word	Meaning
Waning	To shrink in size. As the moon goes through its phases from a full moon to a new moon, it is waning. It goes from a full moon, to a waning gibbous, then to its last quarter, followed by a waning crescent. Finally it becomes a new moon, ready to go through its waxing phases.
Waxing	To grow in size. As the moon goes through its phases from a new moon to a full moon, it is waxing. It goes from a new moon, to a waxing crescent, then to its first quarter, followed by a waxing gibbous. It then becomes a full moon, followed by its waning phases.
White Dwarf	A small, faint and dense star, usually reaching the end of its life. The Sun is currently a yellow dwarf. It will grow to become a red giant before shrinking into a white dwarf after losing most of its gases to space.

Word	Meaning
X-ray	A type of electromagnetic radiation that the?Sun?produces. X-rays cannot be seen, but are very powerful and can penetrate solid objects.
Xena	Dwarf planet?Eris?was discovered in January 2005 but until it received its official name in August 2006, it was informally referred to as Xena. Its name was inspired by the title character in the TV show,?Xena: Warrior Princess.
Year	The length of time it takes for an object, usually a planet, to complete an orbit of the Sun.
Yellow Dwarf star	A yellow dwarf is a star like the Sun. It is a main sequence star, meaning that it has formed and is going through is usual day-to-day existence of making heat and light by converting hydrogen into helium. Yellow dwarf stars are actually usually white. The Sun only appears yellow due to filtering in Earth's atmosphere. Yellow dwarfs usually stay in their yellow dwarf-like state for about 10 billion years, before heating up and expanding to become a red giant, and eventually eventually becoming a small white dwarf. A yellow dwarf might also be known as a G-type main sequence star.
Ymir	A moon of Saturn, discovered in 2000 by a team of astronomers led by Brett James Gladman at the C?te d'Azur Observatory. It has a diameter of about 18 kilometres (11 miles) and takes over 3 and a half Earth years to get around Saturn. It received its name in 2003, named after a creature in Norse mythology. Ymir was a giant and the ancestor of all of the frost giants, two of which (a son and a daughter) were born from his armpits. Lovely. Even better, his feet gave birth to another son, a six-headed monster.
Z?llner, Johann Karl Friedirch	German astrophysisist who made the first measurement of the apparent magnitude of the Sun, being only 0.1 out. He also studied optical illusions and the paranormal. He lived from 1834 to 1882. There is a crater on the Moon named after him.
Zenith	Look up, straight up. The point in the sky directly above you is the zenith.
Zodiac	The Zodiac is the part of the sky that contains the constellations that are situated along the ecliptic, the path that the Sun appears to take across the sky as a year passes (in reality, it is Earth's changing position throughout the year as it orbits the Sun that causes the Sun to move through the constellations). The constellations, or signs of the Zodiac, are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Saggitarius, Capricorn, Aquarius and Pisces. The constellation that the Sun was passing through when you were born is what determines your star sign.? Astrologers believe that a person's destiny is based on their star sign and the changing positions of the objects in the night sky. But astronomy and astrology don't mix too well, so we'll say no more about it. .
Zwicky, Fritz	Swiss astronomer who worked at the California Institute of Technology. He and his colleague Walter Baade came up with the term supernova to describe the explosion of a dying star and their resultant neutron stars. He "observed" dark matter and calalogued loads of galaxies. He lived from 1898 to 1974 and has both a crater on the Moon and an asteroid named after him.

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