If you live in a large town or city, even on a clear night you may only I be able to see a few dozen stars against the light pollution in the sky. In a really dark location, you may see thousands of stars glittering above you. But even then, some stars will be noticeably brighter than others, and the brightest ones will be the same select few that city dwellers see. These brightest stars have been a familiar sight to humans since ancient times.
There are several reasons why some stars look brighter than others. Perhaps the most obvious is that they’re all located at different distances from us. It’s no surprise that, other things being equal, the nearer stars tend to look brighter than ones that are farther away. Our closest star – by a long way – is the Sun, and when it’s in the sky it shines so brightly that we can’t see the other stars at all. A second reason for the differences in brightness is that some stars are larger than others. Our Sun is in the prime of its life – referred to as the main sequence of stellar evolution – but stars that are further advanced in their life cycles can grow to giant proportions. Unsurprisingly, a giant star will be much brighter than a main sequence star seen at the same distance.
There’s one other key factor that makes some stars brighter than others, and that’s their temperature. Hot stars tend to produce more light than cooler ones. We can get a rough idea of a star’s temperature based on its colour. Blue stars are the hottest, followed by white, yellow
