They were very rare from 1645 to 1715, a period called the Maunder minimum.
The Wolf number is calculated using k, the observatory factor, and the number of these present at any given time. They were very rare from 1645 to 1715, a period called the Maunder minimum. Spörer's law states that they usually appear in higher latitudes and later move towards the equator. Their area and latitudinal distribution is graphed against against time in a butterfly diagram, showing a cycle that repeats every eleven years. Coronal mass ejections and solar flares occur near groups of these features. Arising from increased magnetic activity inhibiting convection and thus lowering the surface temperature, for 10 points, name these dark regions on the surface of the sun.
The Wolf number is calculated using k, the observatory factor, and the number of these present at any given time.
{sunspots} (prompt on {starspot} )