July 7, 2025
On this date in 1816, Rudolf Wolf was born. Wolf was a Swiss astronomer best known for his discovery of the Sun’s 11-year sunspot cycle. In 1849 he created a system for counting and tracking sunspots known as Wolf numbers, which is still utilized today.
The image to the left is a portrait of Rudolf Wolf taken between 1888 and 1893. The image on the right is the largest sunspot recorded during solar cycle 24, the most recent solar cycle to complete. The cycle lasted from 2008 to 2019, and the spot occurred near solar maximum on October 18th, 2014. This spot was almost 80,00 miles across, which means you could fit 10 Earth’s across its diameter! We are currently in solar cycle 25 and predicted to be in maximum now. During solar maximum there is an uptick in solar activity which leads to more sunspots.
Images courtesy of NASA/Wikimedia Commons
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