Following a Giant Sunspot

November 15, 2020  •  1 Comment

For once, I was able to follow a sunspot all the way across the face of the Sun. This is a particularly large sunspot group, especially interesting since there have been very few spots of any size for several years. This isn't particularly unusual since the Sun goes through periods when there are more or fewer sunspots over a cycle of 11 years. We are just coming out of a rather deep sunspot minimum though so it was a little surprising to see such a large group. I heard about this new active region from a notification from, a great resource for all things related to the Sun and the solar environment.

Sunspots are immense magnetic storms in the upper layers of the Sun, often covering an area larger than the Earth. They're dark because they are cooler than the surrounding area and produce less light — though still tremendously hot, about 6,400ºF compared to 10,000ºF for the visible surface. Also notice the brighter areas around the sunspots, most noticeable when the spots are near the edge of the sun. These are also associated with the magnetic disturbance and are called faculae.

There was enough clear weather in early November to photograph the Sun on 11 consecutive days around the same time each day. On some days there were passing clouds but there was always enough clear sky to get a photo. I tried to get photos at the same time, around midday as much as possible so the times would be spaced evenly. The photo at the top is a composite of the frames showing the group of spots crossing the Sun and changing shape. Sunspots stay pretty much in the same place on the Sun but appear to move across the disk because the Sun is rotating, taking about 25 days to complete one rotation (though since there's no solid surface, the rate of rotation is different at various latitudes). They do move somewhat in latitude (toward or away from the poles) over time though.

Here's a time-lapse video from the same still frames showing the spot crossing. The inset detail shows a large view of the spots as they change and fade toward the end. Some of the changing shape is because we see the surface tilted away from us causing features to be distorted by the foreshortening. But the spots do change as the storm develops and then subsides.

The Sun consists entirely of gas and plasma (ionized gas) at extremely high temperatures and incorporates extremely strong magnetic fields with very complex dynamics. Sometimes the magnetic fields get twisted and produce spectacular events and solar storms, including ejecting vast streams of energetic, electrically charged particles into the Solar System. If these streams hit the Earth they can cause brighter than usual aurora (northern and southern lights) and if strong enough can disrupt electronic communication and can even disable electrical grids and orbiting satellites. These events are more common during times of greater sunspot activity during the 11 year sunspot cycle. 

These photos were made with a Nikon D850 DSLR and Celestron C5 telescope (1250mm focal length, f/10) with a Baader solar filter, mounted on an iOptron CEM25P drive to follow the motion of the sun across the sky. Exposures varied somewhat because of changing conditions, passing clouds, etc., but were approximately 1/5000 sec., ISO 160 (the telescope has a fixed f/10 aperture). I shot numerous photos on each day in order to capture at least some frames that were as clear as possible. The Earth's atmosphere is very dynamic and distorts and blurs the light from the Sun and stars on very short timescales (which we experience as the stars twinkling), especially during the day as the Sun unevenly warms pockets of air. Using a fast shutter speed and taking many frames can help increase the chance of capturing a particularly clear moment.

As an example, these two frames were taken just a second apart, the one on the right is noticeably clearer, revealing some interesting details in the central structures.



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