Active Sun
Written by Fraser Cain
Solar flare on the surface of the Sun. Image credit: NASA
The Sun looks quiet, calm and steady from our perspective here on Earth, but when seen through a telescope, it's another story. There are huge coronal loops and prominences rising above the surface, and sunspots dot the surface. The amount of activity on the Sun rises and falls over the course of an 22-year cycle called the solar cycle. When the Sun has a large number of sunspots, flares are blasting out often and there are huge coronal mass ejections, astronomers call this an "active Sun".
The Sun's magnetic field varies on a 22-year cycle. If you could stand on the surface of the Sun with a compass, it would be pointing towards one pole of the Sun for 11 years, and then it would switch around and point at the other pole for 11 years. So the Sun's configuration takes 22 years to cycle through all its phases.
When the Sun is active, the surface of the Sun can be dotted with dozens of sunspots. These occur when the Sun's local magnetic field in a region is stronger than average. The sunspot cycle and the magnetic reversal cycle are tied together.
Sunspots appear in pairs, connecting a loop of the Sun's magnetic field lines at two points. When gas travels along these looped field lines, you get an arch-shaped solar prominence. But these field lines can suddenly snap, creating a flare. There is a huge release of energy and spray of particles from the Sun – we see their interaction with our atmosphere as the Northern (or Southern) Lights. During the active Sun phase of the cycle, these flares can happen often and be most at their most powerful.
We have written many stories on Universe Today about powerful solar flares. Here's an article about one of the most powerful flares ever recorded. And another about how a flare disabled a Japanese spacecraft.
Astronomy Picture of the Day has had some wonderful photographs of the active Sun. Here's a video of the Sun's surface. And another taken during a total solar eclipse showing the Sun's active corona.
We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.
Filed under: Astronomy
