Your Astronomy for Today: Our Star is a Star

The Sun is a star. That doesn’t surprise too many people these days (except for the usual anti-science, Earth-is-only-6,000-years-old crowd). Yet, for a long time, it wasn’t considered a star. Sure, there were were early Greeks who suggested it might be one, but they didn’t have a lot of luck getting that idea to be taken seriously. In fact, it really wasn’t until about a hundred years ago (or so) that humanity really had the serious scientific chops to measure the Sun, compare it to other stars, and come to the conclusion that it is a star.

Like other stars, the Sun has nuclear fusion going on in its core. That’s a process that takes hydrogen atoms and fuses them together (this requires high pressures and temperatures to achieve).  The process creates helium, and releases heat and light.  The Sun has been doing this since it first turned on, 4.5 billion years ago. It will continue to fuse hydrogen to helium for a few billion years yet. Eventually it will run out of hydrogen and start to fuse helium to make carbon. At the same time, gravity will cause the Sun to compress under its weight. At the same time, its atmosphere will start to expand to let off all the additional heat created when helium is fused. It will become a red giant for a time, expanding out to engulf most of the inner solar system and warming up the gas giants.

Eventually, the Sun will lost most of its outer atmosphere to space, and what’s left of our star will slowly contract to become a white dwarf. It will still be a star, just a tiny, massive, slowly cooling one.

And that, friends, is your moment of solar zen for today.