The Universe - everything there is. Clusters and super-clusters of galaxies make up of filaments and void, like a complex web.
Galaxies - Groups of stars, containing billions of stars, often with stars orbiting a central black hole.
Stars - a luminous object consisting mainly of hydrogen undergoing fusion kept together by its own gravity.
Planets - large objects with regular eliptical orbits around stars.
Satellites - objects orbiting other objects, most usually orbiting planets, can be natural, e.g. moons, or artificial, e.g. communications satellites.
Moons - a natural object with a regular orbit around a planet.
Dwarf planets - large mass orbiting a star but not having enough gravity to form a regular sphere shape, nor enough mass to clear its orbital path of debris.
Comets - objects orbiting a star which have highly eccentric elliptical orbits.
Asteroid Belt - circular region of our solar system occupied by many rocky objects orbiting the sun. There is one between the terrestrial planets and another out beyond Neptune.
Red-shift - perceived change in wavelength of light due to an object moving rapidly away from an observer.
Big-bang theory - the idea that the Universe started from a single point, followed by a period of rapid expansion.
Cosmic Microwave Background Radiation (CMBR) - the radiation emitted during the initial phase of rapid expansion, it has been redshifting as it travels around the universe and is now in the microwave region of the electromagnetic spectrum. It comes from every area of space that we observe, It is the confirming piece of evidence for the big bang.
Geostationary orbit - an orbit above the equator with an orbital period of 24 hours, such that the satellite can always be found at the same point in the sky. Useful for communications satellites because line of sight is maintained.
Low Polar orbit - an orbit around the poles of earth, with an orbital period of roughly 60 minutes. Can be above any point on earth very quickly as the earth rotates beneath it. Very useful for spy satellites or other types of surveying, for example weather.
Stellar Evolution / Life-cycle of a star - the phases and transitions in the evolution of a star.
Nebula - a large cloud of gas and dust where stars are born. Areas of nebulas are brought together by gravity, temperature and pressure increase as particles collide more regularly.
Protostar - the initial fusion started as temperature and pressure increases sufficiently, begins giving out electromagnetic radiation.
Main sequence star - the period of a star’s evolution where forces from fusion pressure and gravity are balanced. Hydrogen fusion continues at a more or less steady pace. This is much shorter for more massive stars.
Red Giant - heavier elements are fused, and less energy is liberated, the star cools and expands.
Red supergiant - the name given to a red giant above 1.44 times the mass of the sun.
White dwarf - after red giants outgas their lighter layers a smaller dense core, where some fusion still occurs is left.
Supernova - an explosion as a red supergiant star collapses under its own gravity, with its outer layers bouncing off a very dense core. Elements heavier than iron are fused using energy from this energetic explosion.
Neutron star - the remnants of a smaller supernova, the left over matter is so dense that protons have repelled each other and only neutrons are left.
Blackhole - the rupture in space-time left by the largest supernova. It appears as an infinitely dense object that even light cannot escape the gravitational pull of.