More G Stars

The Sun belongs to a rare class of stars: Class G. Members of this class account for only seven or eight percent of all the stars in the Milky Way galaxy.

A star’s class is determined by its surface temperature, which we see as its color. G stars are in the middle of the temperature scale, so they shine yellow to yellow-white.

Most class G stars are in the prime of life — a span that puts them on the main sequence. They’re steadily “fusing” the hydrogen in their cores to helium. And most G stars will stay in that phase of life for 10 billion years or longer.

Most of them are within about 15 percent of the mass of the Sun. Any heavier and they’d get hot enough to move up to class F or above. Any lighter and they’d be cool enough to move down to classes K or M.

Main-sequence G stars are only a small fraction the size, mass, and brightness of the top stars. But the stars in higher classes are even more rare than G stars. So the Sun, which is near the top of its class, shines brighter than about 90 percent of the stars in the Milky Way.

Not all class G stars are on the main sequence, though. Some are bloated and heavy. Such stars are more massive than the Sun. They’ve burned through their hydrogen, and are fusing other elements. Most such stars are either red or blue. But some are making the transition from one to the other, so they briefly shine yellow-white — the monsters of class G.

Script by Damond Benningfield

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