Earth's Star | Universe Today

Written by Fraser Cain

Earth's star is the Sun, of course, a main sequence yellow dwarf star located about 150 million km away. Let's take a look at the nearby star that's so familiar to us, and yet still has a few mysteries left to give up.

The Sun isn't an average star. No, if you wanted to look at the most common stars in the Universe, you'd be looking at a red dwarf. These are tiny stars with less than 50% of the mass of the Sun. The Sun is larger and more massive, and has a surface temperature of about 5,800 Kelvin. It's this surface temperature that gives the Sun its yellow/white light.

The Earth's Star is in the main sequence phase of its life, converting hydrogen into helium at its core with nuclear fusion. 600 million tons of hydrogen are being converted into helium every second. In fact, the Sun consumes the equivalent mass of the Earth every 70,000. The Sun has been in this main sequence phase of its life for 4.5 billion years, and will probably survive for 7 billion more years.

But the Sun won't last forever. When it does run out of fuel in its core, nuclear fusion will stop. The outward light pressure will cease and the Sun's gravity will start to pull itself inward. But then the higher pressure will allow a shell of hydrogen to ignite, pushing the outer layers out into a huge red giant. The Earth's star will expand out to the point that it engulfs the orbits of Mercury, Venus, and yes, even the Earth. A few hundred million years later, the Sun will eject its outer layers. All that will remain is a white dwarf remnant. This hot dead star will cool down over the course of the next trillion years until it matches the background temperature of the Universe.

We have written many articles about stars here on Universe Today. Here's an article about that talks about the Sun's future as a red giant, and here's an article about the Sun's magnetic fountains.

Want more information on stars? Here's NASA's World Book on Stars, and more information from NASA's imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

Filed under: Astronomy