Astronomical distances are expressed using three specialist units: Astronomical unit: average distance between the Earth and the Sun Light-year: distance travelled by light in a vacuum in a time of one year Parsec: the distance from which a base length (radius) of 1...
When electrons are bound to their atoms in a gas, they can only exist in one of a discrete set of energies referred to as energy levels. Energy levels are negative because energy is required to remove an electron from the atom; an electron with zero energy is free...
Astrophysics definitions: Planets: an object in orbit around a star which has 3 characteristics: Mass large enough for its gravitational attraction to give it a round shape No fusion reactions Has cleared its orbit of most other objects, e.g. asteroids Planetary...