BLUE GIANTS

The basic definition of a ‘giant’ star is one that is more luminous than a main sequence star. As the name suggests, part of the reason for this is simply that such stars are enormous in size. That’s particularly true of the most common kinds of giant stars: red giants. Most stars, including our Sun, will eventually end up as red giants, and that’s the case with blue stars too. Earlier in their lives, however, the latter will have spent time as blue giants and supergiants, and these are ‘giants’ due as much to the huge amount of energy they

radiate as to their physical size. Rigel, for example, a blue supergiant in the constellation of Orion, is ‘only’ 79 times the diameter of our Sun, compared to more than 550 times in the case of the red supergiant Betelgeuse in the same constellation.