'In 1843 Heinrich Schwabe noted that the number of these dark areas varies in a periodic cycle'
sunspots
OF THE SUN: In 1843 Heinrich Schwabe noted that the number of these dark areas varies in a periodic cycle
In 1843 Heinrich Schwabe noted that the number of these dark areas varies in a periodic cycle
In 1843 Heinrich Schwabe noted that the number of these dark areas varies in a periodic cycle
OF THE SUN
sunspots
OF THE SUN