Sunspots Appear and Move Away - April 2013

Between April 17 and 26, 2013, a large sunspot group appeared suddenly on the Sun and then rotated out of view. 

The images in this series were taken over the course of nine days, using a hydrogen-alpha telescope, at the Phoebe Waterman Haas Public Observatory.

During this time period, the Sun surprised us by producing a large sunspot group very suddenly; it appeared almost overnight. Normally sunspots take several days to grow as large as these did in a few hours.

On April 17, as you can see in the top left image, there were no sunspots in the upper half of the Sun. Images from NASA show a similarly blank area on the Sun through April 19.

But by April 20, shown in the top right image, a large group of sunspots had formed just above the Sun’s center. These sunspots contained very strong magnetic fields, which are capable of producing powerful solar flares. However, this sunspot group only generated a few weak flares, even though the sunspots were growing larger each day.

On April 24, the Sun had rotated enough that the sunspot group was getting close to the Sun's right edge. In the three images on the bottom row, taken on consecutive days, we see the sunspots moving to the right and disappearing around the curve of the Sun.

The Sun's rotation causes sunspots to move from left to right as seen from Earth. Early scientists observed this sunspot movement and used it to calculate how fast the Sun rotates, about once per month.