Sunspot
Written by Fraser Cain
Almost any picture you see of the Sun will show sunspots. These are dark dots on the surface of the Sun, and they're even visible from Earth without a telescope. Galileo was the first to point a telescope at the Sun and see sunspots, but it wasn't until recently that astronomers had a good explanation for what causes them.
We now know that sunspots are regions on the Sun's surface that have a lower temperature than their surroundings. While the surface of the Sun is approximately 5,800 Kelvin, a sunspot can be merely 4,000-4,500 Kelvin. They're still extremely hot, but this is enough of a temperature difference that they look dark in comparison. These features can be so large that the Earth could fit within an average-sized sunspot.
Astronomers have been tracking the number of sunspots for more than 100 years, and they've learned that the number of sunspots on the Sun's surface rises and falls in an 11-year cycle.
Sunspots happen when magnetic field lines from the Sun get wound up to the point that they puncture the Sun's surface. At these points, convection – or transfer of heat – is inhibited, and the region cools down a little compared to its surroundings. Sunspots tend to last about 2 weeks. This is how long it takes for the magnetic field lines to sort themselves out again.
A sunspot can be broken into two parts: the central umbra and the surrounding penumbra. From within the central umbra region, the magnetic field lines are perpendicular to the Sun's surface, and are roughly vertical. Within the penumbral region, the field lines are inclined at an angle.
Coronal mass ejections are explosions on the surface of the Sun that can through out enormous amounts of material. They usually blast out of regions dominated by sunspots.
We have written many articles about sunspots on Universe Today. Check out this article that talks about the solar minimum, when there aren't any sunspots, and here's a technique you can use to see sunspots for yourself.
We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.
Filed under: Astronomy
