A periodic (regularly repeating) disturbance that transports energy from one place to another, characterised by its wavelength, frequency (or period) and amplitude.

The distance between one part of the wave profile, (e.g. the peak of the wave) at a particular instant in time, and the next identical part of the wave profile at the same instant in time. Wavelength λ is related to frequency f and speed v of a wave by v = fλ.

A small hot star, left behind when a red giant throws off its outer layers as a planetary nebula. A white dwarf has a mass similar to that of the Sun, but a radius similar to that of the Earth. A white dwarf is supported against gravity by an effect of quantum physics known as electron degeneracy pressure.