Active Region on a Sunspot-less Sun
Taken by Mark Townley on July 14, 2018 @
Brierley Hill, UK
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Details:
SDO/HMI says the sun is blank, there are no sunspots. This is only partly true; it is blank in white light but in Hydrogen Alpha light there is a large active region mid disk, however there are no sunspots. Why is this? Well sunspots only form when the magnetic field strength is greater than 1500 gauss. You can see in the image there are quite clear magnetic field lines in the plasma from a bipolar magnetic field with bright plage where the sunspots should be. This is what we would expect given we are in a declining phase of the solar cycle, and scientists have been saying for some time the average magnetic field strength of the sun is also in decline. Maybe these 'white sunspots' will be more common in the next solar cycle which is forecast to be less active than the current one.
Photographer's website:
http://https://brierleyhillsolar.blogspot.com/
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