Planet Earth and Beyond Glossary

  • Alpha Centauri: our second closest easily visible star after the Sun; it is actually two stars orbiting very close together

  • amplifier: a device which amplifies (to make something bigger) the radio wave signals

  • antenna: the dish or other device used to collect radio waves in a radio telescope

  • asteroid belt: the area where most asteroids are found in our solar system, lying between the orbits of Mars and Jupiter

  • asteroid: a small rocky object orbiting the Sun

  • astronomical unit (AU): the average distance between the Earth and the Sun, equal to around 150 million kilometres

  • celestial: positioned in or relating to the sky, or outer space as observed in astronomy

  • chromatic aberration: an optical effect where different colours are refracted by different amounts in a lens leading to a distorted image

  • comet: a small object made of ice and dust which sometimes enters the inner solar system; when a comet enters the inner solar system, part of it evaporates to form a long tail of ice and dust pointing away from the Sun

  • constellation: a group of stars that form a pattern in the sky when viewed from Earth

  • convection: one of the three ways to transport heat energy (the other two are conduction and radiation); as a liquid or gas is heated, it becomes less dense and rises; while denser colder material sinks, creating a flow of moving liquid or gas which transports heat energy along with it

  • dwarf planet: a large, roughly spherical object orbiting a star which cannot be classed as a planet because it is not large enough to sweep out other objects from its orbit

  • filament: a threadlike structure in space containing galaxies and galaxy groups and clusters

  • galaxy bulge: a spheroidal (rugby ball shaped) distribution of old stars at the centre of a galaxy

  • galaxy cluster: a collection of over 50 or more galaxies, held together by gravity

  • galaxy disk: the flat distribution of stars, gas and dust in a galaxy

  • galaxy group: a collection of about 50 or less galaxies, held together by gravity

  • galaxy: a collection of millions or billions of stars, gas and dust all held together by gravity

  • gas giant: a large planet made mostly of gas with no solid surface; the four outermost planets in the solar system are gas giants

  • habitable zone: the region surrounding a star in which water can remain in its liquid state

  • Kuiper Belt object: a small icy object orbiting the Sun out beyond the orbit of Neptune

  • Kuiper Belt: region of space filled with trillions of small objects that lie in the outer reaches of the solar system, past the orbit of Neptune

  • light hour: the distance that light travels in one hour

  • light minute: the distance that light travels in one minute

  • light year: the distance that light travels in one year

  • nuclear fusion: the process by which stars produce their energy; light atomic nuclei come together and merge to form heavier atomic nuclei, releasing energy as they do so; in the Sun, hydrogen nuclei fuse with other hydrogen nuclei to form heavier helium nuclei

  • Oort Cloud: a hypothetical huge cloud of icy objects (comets) surrounding the Sun at the very edge of our solar system at a distance between 5,000 and 100,000 times the Earth's distance from the Sun

  • photosynthesis: the process by which green plants and some other organisms use sunlight to synthesise foods from carbon dioxide and water producing oxygen as a byproduct

  • primary mirror: the light-collecting mirror in an optical telescope

  • Proxima Centauri: our second closest star after the Sun

  • receiver: a device that detects radio wave signals

  • SALT: the Southern African Large Telescope, the largest optical telescope in the southern hemisphere

  • SKA: the Square Kilometer Array, the largest planned radio telescope array in the world

  • solar system: the Sun, and the collection of planets and smaller objects that orbit around the Sun

  • solar wind: the continuous flow of charged particles from the Sun that extends out to the far reaches of the solar system

  • spiral arm: a region of stars, gas and dust forming a curved shape spiraling out from the centre of a spiral galaxy

  • star: a huge ball of burning gas which emits energy in the form of light and heat

  • starlore: mythical stories about the stars, planets and constellations

  • sunspot: a dark region or spot which appears on the surface of the Sun from time to time; sunspots are cooler than the rest of the Sun's surface

  • telescope: an instrument used to look at distant objects, which makes distant objects appear brighter, larger and clearer. Some telescopes collect visible light (optical telescopes) and some collect radio waves (radio telescopes)

  • terrestrial planet: a planet with a rocky surface like the Earth's surface; the four innermost planets in the solar system are terrestrial planets

  • Universe: all of existence, including all planets, stars, galaxies, the space between objects, and all matter and energy

  • void: a vast empty bubble in space found between filaments