He found that the number of sunspots rose and fell in a nearly regular cycle, lasting about 11 years. Interestingly, it soon turned out that big magnetic storms when the magnetic field was disturbed (typically by up to 1%) seemed to occur most frequently during the years with the most sunspots.
1 There are three stages of interphase: G1 (first gap), S (synthesis of new DNA), and G2 (second gap).  Cells spend most of their lives in interphase, specifically in the S phase where genetic material must be copied.
Image of the cell cycle. Interphase is composed of G1 phase (cell growth), followed by S phase (DNA synthesis), followed by G2 phase (cell growth). At the end of interphase comes the mitotic phase, which is made up of mitosis and cytokinesis and leads to the formation of two daughter cells. Mitosis precedes cytokinesis, though the two processes typically overlap somewhat. Image credit: The cell cycle: Figure 1 by OpenStax College, Biology (CC BY 3.0).