This page is meant to make it easier for you to understand the content of this web site. The glossary contains both astronomical and art terms.
Absolute magnitude: The actual brightness of a star. It is defined as the apparent magnitude a star would have if it were located at a distance of 10 parsecs (32.6 light years away).
Accretion disc: The process of growth of an object due to the gradual accumulation of material. An accretion disc can sometimes be found around black holes, pulsars, protostars and protoplanets.
Active galaxies: Galaxies that release huge amounts of energy, mostly long-wavelength radiation, such as radio waves. A common type of active galaxies are Seyfert galaxies.
Aphelion: The point in a planet's orbit around the sun on which it is furthest. Orbits are very rarely perfect circles, but rather eliptic.
Apogee: The point in the moon's orbit around the earth on which it is furthest.
Asteroid: A large piece of rock, sometimes many kilometres across. 'Ceres' is a well known asteroid, and among the largest: approximately 1000 km across.
A large 'belt' of asteroids. Generally when you use the term 'asteroid belt' you speak of the asteroid belt which lies between mars and jupiter. Though there are asteroid belts orbiting other stars.
Astrology: A non-scientific and erroneous study of how the planets affect humans.
Astronomical art: Sometimes considered the same as space art. This form of art strives to illustrate the universe with scientific accuracy, that is: little is drawn from the imagination. This art genre also includes astronomical hardware, such as spaceprobes.
Astronomy: The science of the universe.
Atmosphere: A layer of gas around a planet, moon or star. The atmosphere of earth is essential to life. Not all celestial objects have atmospheres.
AU (astronomical unit): The average distance between the sun and the earth, about 150 000 000 000 metres.
Aurora australis: Also known as southern lights. It appears in the far south of the southern hemisphere.
Aurora borealis: Also known as northern lights. It appears in the far north of the northern hemisphere.
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