Virtually all of the light that we can see in the heavens has come from the surface of stars and they are, certainly for our existence, the most important objects in the Universe. The heat and light of the Sun sustain life here on Earth, and the life cycles of stars that existed billions of years ago produced the elements of which we are made and that of the planet on which we live. This chapter will discuss the properties of stars in general, how these are measured, and where our own star, the Sun, is positioned amongst them.

Stellar luminosity

Stars have a very wide range of intrinsic luminosity – their energy output across the whole electromagnetic spectrum. The luminosity (3.86 × 1026 W) of our Sun, Lsun, is taken as the reference point. The Sun actually turns out to be quite a good star to take as the reference luminosity, as it lies roughly halfway (on a logarithmic scale) between the faintest and brightest stars.