Space Words
Asteroid Asteroids are chunks of rock and metal left over from when our Solar System formed. Most can be found between Mars and Jupiter, a region of space we call the Asteroid Belt.
Asteroid Belt The asteroid belt is a region of our Solar System between Mars and Jupiter. It is heavily populated by asteroids and dwarf planets.
Astronomical Unit An astronomical unit is the average distance between the centre of the Earth and the centre of the Sun (about 150 million kilometres).
Atmosphere An atmosphere is a layer of gases surrounding a planet or a moon. Earth’s atmosphere contains the oxygen we breathe.
Atoms Atoms are the building blocks of the Universe. All matter is made of these tiny particles. Your body contains billions and billions of atoms!
Big Bang Around 14 billion years ago the entire Universe was inside a bubble thousands of times smaller than a pinhead. Then it exploded and the Universe was born.
Billion A billion is a thousand million (1000, 000, 000).
Binary System Four out of every five points of light we see in the night sky are not one star, but two or more orbiting around each other. We call a system of two stars a binary system.
Black Dwarf A black dwarf is the very last phase in the lifecycle of a star like our Sun. When the star has cooled down so much that it no longer shines at all it becomes a black dwarf.
Black Hole Black holes form when a massive star dies and is squashed down into an incredibly tiny space. Black holes' very strong gravity can even swallow-up light if it gets too close.
Brown Dwarf Brown dwarfs are called “failed stars” by some astronomers. Unlike stars, they never become hot enough to start giving off energy in a process called ‘nuclear fusion’.
Comet Comets are made of ice, dust and rock, so they are sometimes called “dirty snowballs”. They come from the outer regions of the Solar System and travel around the Sun, like planets.
Corona The corona is an envelope of blisteringly hot gas surrounding the Sun.
Cosmic Dust Cosmic dust is made up of tiny solid particles in space, sometimes called stardust. You could fit dozens of these particles onto a pinhead.
Dark Energy Astronomers know how much dark energy there is (roughly 68% of the Universe) because they know how it affects the Universe. Other than that, it is a complete mystery.
Dark Matter Dark matter is a mysterious material that got its name because it doesn’t give off any light. There is 5 times as much Dark Matter in the Universe as there is normal matter.
Dark Nebulae Dark nebulae look like holes in the night sky, they are completely black. However, they aren’t empty; dark nebulae are thick clouds of cosmic gas and dust that block out light.
Density Density is a measurement of how much material an object has. For example, a balloon and a bowling ball could be the same size, but the bowling ball has a higher density.
Diameter Diameter is a measurement of the distance across the widest part of a circle or sphere. For example, the diameter of Earth is 12,700 kilometers.
Dwarf Galaxy Dwarf galaxies are much smaller than normal galaxies. They are made up of just a few billion stars rather than hundreds of billions.
Dwarf Planet A dwarf planet is an object in the Solar System that is bigger than a comet or asteroid but smaller than a planet. Our Solar System has five dwarf planets, including Pluto.
Earth Earth is our beautiful home planet; the only place in the Universe where life exists (that we know of)!
Elements There are over a hundred different types of atom, called elements. The atoms of a particular element are identical to each other. Examples of elements are Oxygen, Iron and Gold.
Elliptical Galaxy There are three types of galaxy which all have different shapes. Elliptical galaxies are shaped like rugby balls. These are old galaxies with no new stars forming.
Emission Nebulae Emission nebulae are clouds of cosmic gas and dust that have been heated by nearby stars. As the clouds cool down they begin to shine (the same way a neon light works).
Exo-planet An extrasolar planet (exo-planet for short) is a planet that orbits a star beyond our Solar System.
Force A force is a push or pull on an object. Examples of forces are friction and gravity.
Galactic Bulge In a spiral galaxy the bulge is a spherical-shaped area at the centre of the galaxy. The bulge is made up of old stars as well as cosmic gas and dust.
Galactic Disc Spiral galaxies are disc shaped, like a CD with the bulge at the centre. We call the flat region the galactic disc, it is made up of gas, dust and young stars.
Galactic Halo Each galaxy is surrounded by a halo of material, including very old stars clusters, cosmic gas and dust, and even dark matter.
Galaxy A Galaxy is a gigantic collection of stars, along with cosmic gas, dust and other stuff. The galaxy we live in is called the Milky Way.
Gamma Rays Gamma rays are a type of invisible light. Gamma rays are the most energetic type of light, they are produced by the most violent events in the Universe, like supernova explosions.
Gas Giant Jupiter, Saturn, Uranus and Neptune are called the gas giants because they are much larger than the four planets in the inner Solar System and are made of gas.
Globular clusters Globular clusters are huge groups of stars bound together by gravity. These groups are sometimes made up of hundreds of thousands, or even millions, of stars.
Gravitational Lensing Massive structures like galaxies and clusters of galaxies can bend the light from objects behind them with their strong gravity. This phenomenon is called 'gravitational lensing'.
Gravitational Waves Gravitational waves are created by violent cosmic events, like an exploding star or two black holes colliding. Like ripples on water, these are ripples through space-time.
Gravity Gravity is a force that attracts all objects that have mass. It keeps your feet on the ground and keeps the Earth and all the other planets in orbits around the Sun.
Infrared Infrared is a type of invisible light. The human body has a temperature that gives off infrared light, so infrared detectors can be used as night-vision cameras.
International Space Station The International Space Station is the biggest man-made object orbiting Earth. It is basically a space laboratory where astronauts live and running lots of science experiments
Interstellar Medium The interstellar medium (or ISM) is the material that exists in the space between the stars. This mostly includes cosmic gas and dust.
Irregular Galaxy There are three types of galaxy which all have different shapes. Irregular galaxies come in many different shapes and sizes.
Jupiter Jupiter is the biggest planet in our Solar System, over 100 times bigger than Earth! Jupiter is made up of gas that form cloudy belts that can even be seen with a small telescope.
Kuiper Belt The Kuiper Belt ("KAI-per") is a cold, dark region of our Solar System beyond Neptune. Astronomers believe it contains thousands of comets, asteroids and other small, icy objects.
Light Year A light year is a unit for measuring distance (like a mile or a kilometre). A light year is the distance that light can travel in a year – which is about 9.4 trillion kilometres!
Lunar Eclipse When the Earth passes between the Moon and the Sun, the Moon becomes completely cloaked in shadow. This is called a ‘lunar eclipse’
Magnetic Field A magnetic field is the area around a magnet where the attractive or repulsive force of a magnet can be felt.
Man-made Satellites A number of man-made satellites that have been launched into orbit. They carry out a range of jobs, including collecting information, helping us communicate or for navigation.
Mars Mars is also known as The Red Planet. Mars is one of our closest cosmic neighbours and the only planet in the Universe entirely inhabited by robots!
Mass Mass is a constant measurement that shows how much material an object has. Unlike mass, weight is the pull of gravity on an object and it changes depending on gravity.
Mercury Mercury is the closest planet to our Sun and the smallest planet in the Solar System. It’s not much bigger than our Moon and looks very similar — rocky and covered in craters.
Messier Objects The Messier Catalogue is a list of 110 cosmic objects created by a French astronomer named Charles Messier in the 1700s.
Meteor When a meteoroid enters Earth’s atmosphere it creates a streak of light, this is known as a meteor or sometimes a ‘shooting star’.
Meteorite If a meteoroid, comet or asteroid lands on Earth it’s called a meteorite. Around 50,000 tonnes of meteoroids and other kinds of space dust enter our atmosphere every year!
Meteoroid A meteoroid is a small rock travelling through space. Meteoroids are much smaller than asteroids; they range from the size of a rice grain up to a metre wide.
Microwave Microwaves are a type of invisible light. Microwaves are good for sending messages from one place to another because microwaves can travel through rain, snow and clouds.
Milky Way The Milky Way is the galaxy we live within. The Sun is one of 100 billion stars in the Milky Way.
Million A million is a thousand, thousand (1,000,000).
Molecules A molecule is a particle containing two or more atoms. For example water is a molecule made up of two atoms of hydrogen and one atom of oxygen.
Moons A moon is a natural satellite that orbits a planet. Most of the planets in our Solar System have at least one moon, like Earth, some planets have dozens.
Natural Satellites There are two types of satellite: natural and man-made. Natural satellites are cosmic objects that orbit around other objects in space, e.g. the Moon which orbits around Earth.
Near Earth Objects A near-Earth object (shortened to NEO) is any small object in the Solar System, such as asteroids or comets, that travels close to Earth.
Nebula A Nebula is a cloud of gas and dust in space. Some are the remains of dead stars and others are where stars are born.
Neptune Neptune is the farthest planet from the Sun, it takes over 60,000 days to complete one orbit! Like Jupiter, Saturn and Uranus it is a gas planet.
Neutron Star When a huge star reaches the end of its life, it explodes. The core of the star survives the explosion, but is squashed down into a tiny compact ball called a neutron star.
Oort Cloud Most astronomers believe the Oort Cloud (pronounced "O-rt") is a giant icy shell made of comets that surrounds our Solar System.
Open clusters Open clusters are groups of stars that formed from the same giant cloud of gas and dust. These groups contain up to a few thousand stars that are loosely bound together by gravity.
Orbit An orbit is the path along which cosmic objects, satellites and even spacecraft travels. For example, the Earth’s orbit around the Sun takes 365 days to complete (or one year).
Planetary nebula Planetary nebulae have nothing to do with planets. They are clouds of cosmic gas and dust created when a Sun-like star blows off its outer layers of material.
Planets A Planet, such as Earth or Jupiter, is a large object that orbits a star such as the Sun. A planet doesn’t make its own light.
Protoplanetary Disc A protoplanetary disc is a ring of cosmic gas and dust surrounding a very young star. The disc might one day form into a system of planets and moons like our Solar System.
Pulsar Pulsars are extremely compact stars that spin around hundreds of times a second. Pulsars shoot out radio waves that shine towards us on Earth in pulses, like a lighthouse.
Radio Radio waves are a type of invisible light. Radio waves are mostly used in communications to send signals from one place to another. Mobile phones and TVs use radio waves.
Red Dwarf A red dwarf is a star that is very small and cool compared to other stars. These stars appear red because of their temperature (the coolest stars are red).
Red Giant When a star like the Sun runs out of hydrogen fuel to burn it begins to grow bigger and redder, turning into a red giant star.
Reflection Nebulae Reflection nebulae are clouds of cosmic dust that reflect the light of a nearby stars. These clouds are usually blue.
Robot A Robot is a machine controlled by a computer. Robots can be taught to do many different things, like clean a carpet, control a telescope or even build a car!
Saturn Saturn is the sixth planet from the Sun and probably the most beautiful. Saturn is famous for its bright rings made out of ice, rock and other things.
Solar Eclipse When the Moon passes between the Sun and Earth and blocks out the Sun's light, we call it a ‘solar eclipse’
Solar Rain Just like Earth, it sometimes rains on the Sun. But this rain is not made of water, it is made of electrically charged, superheated gas, called plasma.
Solar System The Solar System is made up of the Sun and everything that moves around it. There are eight planets, five dwarf planets and lots of moons, comets, asteroids and meteoroids.
Spectrograph An instrument that collects light and spreads it, like a prism. Believe it or not, the light reveals signatures of different elements in the atmospheres around stars.
Spiral Galaxy There are three types of galaxy which all have different shapes. Spiral galaxies are the most beautiful, with long star-filled arms twisting around a bright central bulge.
Star A star is a massive ball of luminous hot gas held together by gravity. Our nearest star is called the Sun.
Starburst Galaxy Starburst galaxies are galaxies where stars are being made at a very fast rate, normally about 10,000 times faster than in a normal galaxy!
Star Cluster A Star Cluster is a huge group of stars bound together by gravity. A star cluster can contain a few hundred stars or many millions.
Sun The Sun is a star. It is the centre of our Solar System and everything else in the Solar System moves around it. Without the Sun’s light and heat life could not survive on Earth.
Supernova The explosive death of a massive star is called a supernova. They are amongst the most energetic events in the Universe and are so bright they can outshine an entire galaxy!
Supernova Remnant      A supernova remnant is a cloud of cosmic gas and dust created by the violent explosion of a massive star. The supernova remnant is what remains of the unfortunate star.
Telescope A Telescope is an instrument used to see objects that are very far away. Telescopes are often used to look at distant planets, stars and galaxies.
Terrestrial Planets Mercury, Venus, Earth and Mars are called the terrestrial planets (pronounced "Ter-EST-ree-al"). All four of these planets are similar to Earth in size and are made of rock.
Ultraviolet Ultraviolet (often shortened to UV) is an invisible type of light. UV waves have high energy. UV rays from the Sun are capable of damaging cells in our skin and causing sunburn.
Universe The Universe is everything that exists, all planets, stars, galaxies and every other object on Earth and in space.
Uranus Uranus is a cold blue, gas planet that lies far from the Sun. Unlike all the other planets, Uranus lies on its side, with its South Pole facing the Sun.
Venus Venus is the second planet from the Sun and the hottest planet in the Solar System. Venus is Earth’s twin in size, but unlike Earth it’s covered in ancient volcanoes!
Visible Light Visible light is the only type of light that our eyes can detect. Visible light contains all the colours of the rainbow.
White Dwarf When a Sun-like star has burned up all its fuel, it begins to collapse inwards. The material in the star's core ends up squashed tightly down into a tiny ball called a white dwarf.
X-ray X-rays are a type of invisible light. X-rays can travel through soft tissue like skin and muscle, so they can be used to take pictures of broken bones.

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