Parallax, the apparent motion of a star against the background of a more distant star, due to the motion of the Earth around the Sun. The angle is measured at different times during the year. The distance of the Sun to the Earth is known. At large distances the uncertainty becomes too large and it can't be applied. F.1.3 Apparent magnitude is a measure of observed brightness of a star seen from Earth.
Absolute magnitude is a measure of luminosity, how much light a star radiates into space.
A star seeming just as bright as one close to us, but being further away has a greater absolute magnitude. A black body is a theoretical perfect radiator. Stars radiate energy practically as these. The spectra of light emitted by a source can reveal the chemical composition of the source since the 'emission spectrum' is the material's characteristic since excited gases emit light of only certain wavelengths. Types of stellar objects F.2.1 The Hertzsprung-Russel diagram links luminosity with temperature.