Do you know what a sunspot is? They’re regions of magnetic disturbance on the sun the appear darker than their surroundings because they’re a bit cooler. Sunspots usually appear in pairs with each spot having the opposite magnetic pole of the other.
See those dark smudges in the middle of the sun in this image? Yeah, those are sunspots. They’re constantly appearing, disappearing, and shifting in position on the sun in an 11 year cycle. Don’t be fooled by how tiny those spots look in that image — sunspots at at least as big as the Earth!
The sun isn’t the only star with spots. We now know that other stars have starspots of their own. If you want to know more, UW astronomy grad student Jim Davenport has the scoop on his blog: check it out!