Photo: steviep187 (flickr)
From ancient times, we have tended to think of the sun as perfect, unblemished, and whole. Galileo was therefore somewhat surprised when he aimed his newly invented telescope sunward in 1610.
Instead of a smooth and even surface, he found that the sun was marked by dark spots. These migrated slowly across the sun, disappearing around the edge after a week or so. Galileo concluded, quite mistakenly, that these spots were dark clouds, like thunderclouds, travelling around the sun.
Understanding Of Sunspots
Our understanding of sunspots is now much better. Like the Earth, our sun has a magnetic field, with north and south magnetic poles. Unlike on Earth however, the sun’s magnetic field is very irregular, undergoing constant change.
In fact, the sun’s magnetic field is so chaotic that its north and south poles actually switch position every eleven years. This would be like all the compasses on Earth pointing first north, then changing to south eleven years later.
Where Do Sunspots Occur?
Sunspots occur at places where the sun’s irregular magnetic field is highly concentrated. The sun’s surface is usually reheated by a continual flow of hot material from deep inside the sun.
However, a strong concentration in the magnetic field can interfere with this reheating flow. Sunspots are therefore slightly cooler and darker than their surroundings.
Concentration Of Sunspots
Because the sun’s magnetic field reverses regularly, the concentration of sunspots also follows an eleven year cycle. At the height of this cycle there can be as many as a hundred spots a day, some larger than the Earth itself. During quieter parts of the cycle, the sun can be completely unblemished.
Don’t try to look for sunspots yourself, even through sunglasses. It is especially dangerous to look at the sun through binoculars, a telescope, or a camera. The only safe way to see what sunspots look like is to find a picture of them.