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Space A to Z

























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.
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.
John Couch Adams When he was 24, English astronomer and mathematician John Adams was the first to predict the location of an object beyond the orbit of Uranus. This object was later found by German astronomer Johann Gottfried Galle in 1646 and became known as Neptune. Galle used predictions of its location by French astronomer Urbain Jean Joseph Le Verrier since Adams didn't publish his findings! Adams lived from 1819 to 1892.
Adrastea Moon of Jupiter, discovered in 1979 by Voyager, 2nd closest moon to Jupiter, diameter 40 km (25 miles)
Aegir One of Saturn's many many many many moons
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).
Albiorix moon of saturn
Edwin "Buzz" Aldrin Apollo 11 astronaut. Second man to walk on the Moon's surface.
Alpha Centauri The 3rd nearest star to Earth, after the Sun and Proximus Centauri. 4.4 light years away. Also the fourth brightest star in the sky, after the Sun, Sirius and Canopus, with a magnitude of -0.3.
Amalthea Moon of Jupiter, discovered in 1892 by Edward Emerson Barnard. 200 km (150 miles) in diameter.
Ananke A Moon of Jupiter
Anthe Moon of Saturn
Aoede moon of jupiter
Aphelion The greatest distance of a planet or comet in its orbit around the Sun. Opposite to perihelion.
Apoapsis The greatest distance of a body (a moon or an artificial satellite) in its orbit around bodies other than the Sun or Earth (for example, a moon around Jupiter).
Apogee The greatest distance of a body (the Moon or an artificial satellite) in its orbit around Earth.
Apollo Name given to missions in the 1960s and 1970s designed to land man on the Moon and return him home. Three astronauts testing Apollo 1 died in a fire in the capsule. Apollo 4 - 6 were unmanned launches. Apollo 7 was a manned launch but didn't go to the Moon. Apollo 8 - 10 were manned launches to the Moon (but were not designed to land). Apollo 11 - 17 were manned missions to land on the Moon. No moon landing took place during Apollo 13 due to an explosion onboard.
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 moon of Jupiter
Arcturus Fifth brightest star in the sky, 36 light years from Earth, magnitude 0.0
Ariel A moon of Uranus
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 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.
Astrology The belief that the positions of the Sun, Moon, stars and planets can affect a person's destiny.
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.
Atlas Moon of Saturn
Atmosphere The layer of gas surrounding the surface of a planet, moon or star.
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 ionopshere). 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"
Autonoe moon of jupiter
Axis The imaginary line around which a planet, moon, star spins.
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 American astonomer. Discovered the fourth nearest star to Earth, which became known as Barnard's Star. Also discovered Amalthea, a moon of Jupiter in 1892. Lived from 1857 - 1923.
Barnard's Star Fourth nearest star to Earth. 5.9 light years away.
Bebhionn Moon of Saturn
Belinda Moon of Uranus. Discovered in 1986 by Voyager 2., approx 80km in diameter, 10th moon is distance from Uranus.
Bergelmir Moon of Saturn, discovered in 2004
Bestla moon of saturn
Bianca moon of uranus
Billion The American version of billion is one thousand million and is written as 1,000,000,000. The English version is one million million and is written 1,000,000,000,000. Scientists generally use the American version, or to avoid confusion, don't use billion at all and keep to scientific notation.
Black Hole The core of a collapsed star. Its gravity is so strong that not even light can escape.
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 Bode to generate the orbits of objects orbiting the Sun in A.U. Although it appears to be accurate for the planets (including the asteroid belt) up to Uranus (it actually predicted Uranus' orbit before it was discovered), it seems to go wrong after that and misses out Neptune. The law appears to back-up theories about how Solar Systems are formed (the distances between planets roughly doubles the further you move out of the Solar System) and it is more coincidental that the positions of objects up to Uranus fit in with Bode's Law.
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.
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 Moon of Uranus. Named after a character in William Shakespeare's play, The Tempest
Callirrhoe Small moon of Jupiter discovered in 1999. About 7 km in diameter.
Callisto Second largest moon of Jupiter, third largest moon in the Solar System. 99% the size of planet Mercury. Discovered by Galileo in 1810, Callisto is the most cratered body in the Solar System.
Calypso A moon of Saturn. Sounds tropical
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 moon orbiting
Carpo Small moon of Jupiter discovered in 2003, only about 2 km in diameter.
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.
Chaldene Small moon of Jupiter, discovered in 2000, about 4 km in diameter.
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.
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 which stay in a cluster by their common gravity.
Coma The "ball" part of the comet, surrounds the nucleus.
Comet Small ball of dust and gas which orbits the Sun, often in elliptical (oval) orbits. Only visible when they are close enough to the Sun to start burning off their dust/gas. Some comets take a few decades to complete an orbit, others take thousands of years. Some comets are also known to orbit Jupiter.
Conjunction A term to describe the position of one planet in relation to Earth. An "inferior conjunction" is when an inferior planet (a planet closer to Earth: either Venus or Mercury) is in between Earth and the Sun. If the inferior planet is on the other side of the Sun to Earth, it is in "superior conjuction." A superior planet (any planet beyond Earth in the Solar System) is "in conjunction" when it is on the opposite side of the Sun. When the superior planet is on the same side of the Sun as Earth, it is then said to be "in opposition".
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 moon of uranus
Corona A uppermost 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 Russian/Soviet word for Astronaut.
Crater An bowl-shaped depression formed when a meteorite hits the surface of a planet or moon.
Cressida moon of uranus
Crust The thin rocky surface of a planet or moon.
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.
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.
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
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.
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
Kiviuq moon of saturn
Kore moon of jupiter
Word Meaning
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.
Light year
Word Meaning
"M" numbers
Magnetic Field
Megaclite moon of jupiter
Methone moon of saturn
Metis moon of jupiter
Mimas moon of saturn
Mneme moon of jupiter
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
Ophelia moon of uranus
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
Pasiphae moon of jupiter
Pasithee moon of jupiter
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
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.
Polydeuces moon of saturn
Prometheus moon of saturn
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.
Word Meaning
Quaoar Small Kuiper Belt object, potential Dwarf Planet.
Word Meaning
Radio Waves
Rhea moon of saturn
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.
Schirra, Walter Apollo 9, Apollo 15 astronaut
Scott, David Apollo 7 astronaut.
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 Craft / Space Probe
Sponde moon of neptune
Star A ball of gas,
Sun Spot
Surtur moon of saturn
Suttungr moon of saturn
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
Thrymr moon of saturn
Thyone moon of jupiter
Titan moon of saturn
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
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
Al-Zarkali, Ab? Ish?q Ibr?h?m Full name Ab? Is??q Ibr?h?m ibn Ya?y? al-Naqq?sh al-Zarq?l?, Al-Zarq?l?, or Arzachel, was an Arab astronomer and astrologer who lived in what is now Spain during the 11th Century. He made several accurate measurements about the motions of the Sun, known planets and Moon. Back then, it was thought that Earth was at the centre of the solar system. A lot of his calculations held true until later astronomers realised that it was actually the Sun at the centre of the solar system. He has a crater named after him on the Moon.
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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