Aerobraking: Procedure in which a spacecraft uses atmospheric drag forces to slow down.
Andromeda: A galaxy, part of the local group.
Asteroid: These are minor planets orbiting the Sun. The total mass of all the asteroids in our solar system is less than the mass of the Moon. The asteroid belt is located between Mars and Jupiter.
Astronaut: A participant in the NASA or ESA human spaceflight programme.
Atlantis: Final shuttle to fly to orbit out of the original four.
Aurorae: Aurorae (singular: aurora) occur when electrically charged particles from the solar wind interact with the magnetic field of a planet. On Earth we know them as the Northern Lights.
Beagle2: Britain's Mars lander and partner of Mars Express. Contact was lost during its descent to the surface.
Big Bang: The most widely accepted theory for the formation of the universe. All the matter that makes up the universe today exploded outwards from a single tiny point.
Binary system: Consists of two stars orbiting a common centre of mass.
Black hole: Extremely dense remnant of a very massive star. Its gravitational attraction is so strong that light cannot escape from it.
Blueshift: The shift of spectral lines towards the blue end of the spectrum. This means that the source is moving towards us.
Borelly: A comet, encountered by the probe Deep Space 1.
Brown dwarf: A star that never became massive enough to start core hydrogen burning.
Callisto: One of Jupiter's Galilean moons
Cassini-Huygens: Cassini Huygens is a joint orbiter/lander sent to investigate Saturn and its moons, particularly Titan.
Cepheid variable star: A star with periodic variations in magnitude (brightness).
Challenger: The second space shuttle to be launched into orbit. It was destroyed in 1986 after an explosion occurred a few seconds into flight.
Chandra: An X-ray observatory in orbit around the Earth.
Charon: Pluro's moon.
Cluster: A group of stars that are close together.
COBE: The COsmic Background Explorer. COBE was launched into Earth orbit in 1989 to image the cosmic background radiation.
Columbia: The first space shuttle to fly into orbit. It disintegrated upon re-entry in 2003.
Comet: A comet is a ball of icy material with a higly eccentic elliptical orbit around the Sun.
Constellation: A group of stars that appear to make a picture in the sky.
Corona: The 'atmosphere' of the Sun that can be viewed during a solar eclipse.
Cosmic Background Radiation: The remnant radiation from the Big Bang. Its distribution in the universe today can tell us about how the universe may have formed.
Cosmonaut: A participant in the Russian human spaceflight programme.
Dactyl: Moon orbiting the asteroid Ida
Deep Impact: Probe sent to comet Tempel-1 with an impactor to see what it is made of.
Deep Space 1: Probe that flew by an asteroid and comet Borelly.
Deimos: Moon of Mars.
Discovery: Third shuttle to fly into orbit. Scheduled return to flight July 2005.
Doppler shift: Generic term encompassing redshift and blueshift.
Earth: A very familiar planet (!), the only one in the solar system known to support life. Third from the Sun.
Eccentric orbit: An orbit that is elliptical, but very far from circular. Generally comets have this kind of orbit. (Planets do have elliptical orbits as well but they are almost circular).
Ecliptic plane: The plane in the solar system within which the planets (most of them) orbit the sun.
Electromagnetic radiation: Electromagnetic radiation is light, but it extends beyond the small proportion of the spectrum that our eyes can see. We can obtain images at other frequencies using cameras sensitive in those frequencies.
Endeavour: Replacement shuttle for Challenger.
ESA: The European Space Agency
Europa: Jupiter's icy Galilean moon.
Extrasolar planet: A planet outside our solar system.
Extraterrestrial life: Life that comes from somewhere other than Earth.
Galaxy: A vast collection of stars, sometimes structured and sometimes not.
Galileo: A probe sent to observe Jupiter and its Galilean moons. Named after the famous Italian scientist.
Galilean moon: A moon of Jupiter discovered by Galileo (the person, not the probe!)
Gamma rays: Very high frequency electromagnetic radiation.
Ganymede: Galilean moon of Jupiter.
Gaspra: An asteroid
Gas giant: A large, icy and gaseous planet in the outer solar system.
Genesis: Probe that returned particles from the solar wind to the Earth in 2004.
Giotto: Probe that flew to comet Halley.
Halley: Probably the most famous comet. Named after Edmund Halley who first predicted the periodic return of comets.
Hiten-Hagomoro: First probe to complete an aerobraking manoeuvre.
Hubble Space Telescope: Telescope in orbit around Earth. Can obtain very high resolution images. Named after Edwin Hubble, an astronomer in the early twentieth century.
Ida: First asteroid with a moon to be discovered.
Infrared: Electromagnetic radiation band just beyond the red end of the visible spectrum.
Io: Jupiter's Galilean moon. Highly volcanic.
ISS: International Space Station, a joint project between NASA, ESA and the Russian Space Agency.
Janus: Moon of Saturn
Jovian moon: Moon of Jupiter
Jovian planet: Another term for a gas giant.
Jupiter: The fifth and largest planet from the Sun. First gas giant.
Keck: A set of giant telescopes in Hawaii
Kuiper Belt: The belt of small planetoids at the outer edge of our solar system.
Lander: A spacecraft that lands on another planet but is not capable of travelling on the surface.
Local group: Galaxies that are part of the cluster around the Milky Way.
Luna: A lunar probe, along with Lunar Orbiter, Lunar Prospector and LUNAR-A.
Magellan: Probe to Venus.
Magellanic Clouds: The Milky Way's two 'satellite' galaxies.
Main sequence star: A star burning hydrogen in its core.
Mariner: Series of probes to Mercury, Venus and Mars.
Mars: The fourth planet from the sun and the most explored, excluding than the Earth. The last rocky planet.
Mars Express: ESA's Mars orbiter
Mars Global Surveyor: Mars orbiter
Mars Pathfinder: Mars lander and rover.
Mars Odyssey: Mars orbiter
Messenger: Probe to Mercury
Mercury: The closest planet to the sun.
Meteorites: Small pieces of rock that enter our atmosphere and gradually disintegrate, before reaching the ground. They are called meteoroids before they enter the atmosphere and meteors whilst they are in the atmosphere.
Microwaves: Electomagnetic waves with a frequency between radio and infrared.
Milky Way: Our galaxy.
MIR: Russian space station.
Miranda: Uranus's moon.
Moon: A natural satellite. We call Earth's moon the Moon.
NASA: National Aeronautics and Space Administration (NOT the North American Space Agency!)
Nebula: An interstellar cloud of dust and gas. Often solar systems form when something causes these clouds to coalesce. These can be formed by the death of a star.
Neptune: The eighth planet from the sun, and the last that truly fulfils the criteria to be recognised as a planet.
Neutron star: A very dense stellar remnant, formed when a star with a remnant bigger than about 1.4 solar masses explodes in a supernova. They spin rapidly.
Opportunity: One of NASA'a current Mars rovers.
Orbit: The elliptical closed path followed by a body under the gravitational influence of another body.
Orbiter: A spacecraft that goes into a sustainable orbit, either around the planet it is meant to be studying or around Earth in order to remain above the atmosphere.
Pandora: Moon of Saturn.
Phobos: Martian moon
Phoebe: Saturn's moon
Pioneer: Probe to the gas giants
Planet: Derived from the Greek meaning 'wanderer', a planet is a body orbiting a star that is not a star itself. The classification also depends on size and orbital eccentricity, with planets generally considered to be quite large and with circular orbits. However, the term is not well defined.
Planetoid/Planetesimal: Planetoids are objects that are larger than asteroids but cannot be called a planet. The term planetesimal is sometimes used to refer to asteroids, but also objects with a specific diameter of approx. 10 km.
Pluto: Ninth and furthest 'planet' in our solar system. Has a very eccentric orbit that is not in the ecliptic plane.
Prometheus 1: Future probe to Jupiter.
Protostar: A star that has not yet started core hydrogen burning.
Quaoar: A planetoid in the Kuiper Belt on the edge of the solar system, about half the size of Pluto.
Radio waves: Very long wavelength electromagnetic radiation.
Ranger: Series of lunar probes.
Red dwarf: Small main sequence star.
Red giant: The phase of a star when all the core hydrogen is used up and the star becomes enlarged. It cycles between shell burning and core burning of successivly heavier elements, up to iron. The number of cycles depends on the mass of the star.
Redshift: The shift of spectral lines towards the red end of the spectrum when the light source is moving away.
Rhea: Moon of Saturn.
Rocky planet: An Earth-like planet, made of rock rather than ice. Generally smaller planets are rocky.
Rosetta: Probe to a comet.
Satellite: A body orbiting another larger body. Generally, we use this term to refer to man-made items in orbit.
Saturn: The sixth planet from the Sun, it has spectactular rings. It is a gas giant.
Sedna: Planetoid recently discovered far beyond Pluto's orbit. It is about three-quarters of the size of Pluto.
Shuttle: NASA's human spaceflight vehicle.
Smart-1: ESA's first lunar orbiter.
Space: The relatively empty parts of the universe.
Soyuz: The Russian Space Agency's spaceflight vehicle.
Spirit: One of NASA's current Mars rovers.
Sputnik: The first spacecraft and satellite ever launched.
Star: Gaseous body that generates energy by a nuclear fusion reaction.
Stardust: Probe to a comet.
Sun: The star at the centre of our solar system.
Surveyor: Series of lunar probes.
Telescope: A tool for gathering and focusing electromagnetic radiation (NOT just visible light). This can be done with lenses, mirrors or gratings.
Terrestrial planet: Earth-like planet - another term for a rocky planet.
Titan: Moon of Saturn
Triton: Neptune's moon. It has a retrograde orbit (orbits in the opposite direction to Neptune's rotation).
Ultraviolet: Electromagnetic radiation that is slightly higher frequency than the blue end of the visible spectrum.
Ulysses: Probe to the Sun.
Universe: The whole of space and time, but often used to describe the parts of it that we can now observe.
Uranus: Seventh planet from the Sun, ringed gas giant.
Venera: Probe to Venus
Venus: Second planet from the Sun.
Venus Express: Future ESA mission to Venus.
Viking: Probe to Mars.
Voyager: Series of probes to the outer solar system.
White dwarf: A small, dense stellar remnant that was formed from a dying star whose dead mass was less than 1.4 solar masses. These are unltraviolet emitters.
XMM-Newton: An orbiting observatory.
X-rays: Electromagnetic waves with a wavelength between those of ultraviolet and of gamma rays.
Zond: Series of lunar probes.