Marianne Dyson, November 2017
Did you know that the sun rotates on its axis about once a month? Since all sides of the sun look essentially the same, how can scientists tell how fast it goes around? The sun has spots! These spots act as markers for what part of the sun is facing Earth. By tracking their motion, scientists can clock the rate of motion of the surface.
A group of sunspots appear near the center of the Sun in this photo taken during the eclipse on August 21. These spots first appeared on the edge of the Sun on August 14.