chapter  19
Stellar Spectra and Evolution
WithPatrick Moore
Pages 12

The stars show a tremendous range in luminosity, though much less in mass. Some known stars are millions of times more luminous than the Sun, while others are remarkably feeble. At its peak, in the 1840s, the erratic variable η Carinas was estimated to be 6000 000 times as powerful as the Sun; S Doradus, in the Large Magellanic Cloud, has an absolute magnitude of −8.9, so that it is at least a million times as luminous as the Sun – yet because of its great distance (170000 light-years) it cannot be seen with the naked eye. At the other end of the scale is MH18, discovered in 1990 by M. Hawkins at what was then the Royal Observatory, Edinburgh, from plates taken with the UKS telescope in Australia. It has 1/20000 the luminosity of the Sun, and is presumably a brown dwarf (see below). Its mass is 5% that of the Sun, and its distance is 68 light-years.