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Video · NASA APOD

Credit: NASA APOD

Counting sunspots…

Image · NASA/ESA SOHO

Sunspots are cooler, darker patches on the Sun's visible surface where intense magnetic fields push up through the photosphere and slow the flow of heat from below. They are typically a couple of thousand degrees cooler than their surroundings, can grow larger than Earth, and drift across the disc as the Sun rotates roughly once a month.

Counting them matters: the sunspot number tracks the Sun's roughly 11-year activity cycle, and the biggest, most magnetically tangled groups are the launch pads for solar flares and coronal mass ejections. Those storms drive aurorae, but can also disturb radio communication, GPS accuracy, satellites and power grids — so daily counts from observatories like SOHO underpin space-weather forecasting and our understanding of stellar magnetism.