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Few Suns

August 20, 2016

Plenty of bright stars decorate the sky on these warm summer evenings. Among others, yellow-orange Arcturus is in the west, red-orange Antares is low in the south, and bright white Vega stands high overhead.

What’s remarkable, though, is that none of the bright stars visible on a summer’s eve is anything like our own star, the Sun. In fact, of all the stars visible to the unaided eye, only a couple of dozen can safely be described as “Sun-like.” And many of those are so faint that you need dark skies to see them.

In part, that’s because stars like the Sun aren’t that common. Stars that are relatively close to the Sun’s mass and stage of life account for only a few percent of all the stars in the galaxy. Most stars are much smaller and fainter than the Sun. Even so, Sun-like stars are so faint that they’re not visible beyond a few dozen light-years.

Most of the really bright stars in the night sky are giants or supergiants. These stars are nearing the ends of their lives, so they’ve puffed up to dozens or even hundreds of times the Sun’s diameter. Such big stars are rare, but they’re dazzlingly bright, so they can be visible from hundreds of light-years away.

Vega and a few other bright stars haven’t yet reached that stage of life — they’re still in middle age, as the Sun is. But they’re a good bit heavier than the Sun, which makes them shine much brighter.

Two Sun-like stars are visible in the western sky at nightfall; more about them tomorrow.


Script by Damond Benningfield

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