Want to stay on top of all the space news? Follow @universetoday on Twitter
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.
Although sun spots are darker than the surrounding regions of the Sun, they’re actually incredibly hot. A sun spot can be more than 3,500 degrees Kelvin. Even though that would be white hot if you could look at it, that’s less bright than the average surface temperature of the Sun, which is 5,800 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.
The Sun is mostly made of plasma, a state of matter which has the additional property of being highly magnetic. Because of the movement of plasma inside the Sun, it generates a powerful magnetic field, similar to the Earth’s magnetosphere. But the magnetic field on the Sun is constantly shifting around. Physicists believe that these magnetic field lines can get so twisted up that they curl up like a rubber band and pierce the outside of the Sun.
Sunspots are created at the points where the Sun’s magnetic field lines pierce through the Sun’s photosphere (the part of the Sun that we can see). Although they look dark, they’re really just a few thousand degrees cooler than the surrounding photosphere, so they’re actually still very hot. The magnetic field lines are loops, so the sunspots appear in pairs; the two points where a single loop comes out of the Sun and then goes back in.
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.
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. At the low point of the cycle, called the solar minimum, there can be few or no sunspots on the surface of the Sun. And then at the high point, the solar maximum, we see the highest number of sunspots.