Kepler's lost sketches reveal sunspot mysteries before maunder minimum

Johannes Kepler, a German mathematician born in 1571, is primarily known for formulating the laws of planetary motion. However, not everyone knows he was also a keen observer of the Sun. In 1607, using a camera obscura, he made important observations of our nearest star. Moreover, his precise drawings in subsequent years enabled astronomers to determine the Sun's position in its 11-year activity cycle.

As reported by Science Alert, Kepler's detailed sketches allowed astronomers to pinpoint the Sun's phase within its 11-year cycle. By analysing his location during the time of sketching and the sunspots' positions in his drawings, a group of researchers concluded that the Sun was nearing the end of the thirteenth solar cycle at that time.

In May 1607, Kepler recorded what was initially thought to be the transit of Mercury, but it ultimately proved to be a group of sunspots. These spots, cooler and darker than their surroundings, have a temperature of about 3200°C compared to the photosphere's average temperature of nearly 5400°C. These temporary solar phenomena can be observed in the photosphere, appearing dark against the hotter and brighter backdrop.

A research team led by Hisashi Hayakawa from Nagoya University used innovative techniques to analyse Kepler's drawings and discovered new information regarding solar activity during that period. Applying Spörer's law, the researchers determined that these observations occurred at the end of the solar cycle, just before the commencement of the well-documented Maunder Minimum—a period of significantly reduced sunspot activity between 1645 and 1715. These findings could enhance our understanding of extended periods of solar inactivity.

"If this is true, it would be really interesting. However, another reconstruction based on tree data suggested a sequence of solar cycles with normal durations," said study author Hisashi Hayakawa from Nagoya University. He added: "So, which reconstruction should we trust? It is extremely important to verify these reconstructions with independent—preferably observational—records."

It is worth remembering that while the Sun may seem unchanging, it undergoes 11-year cycles of fluctuating activity. Although the central body of the Solar System is located about 93 million miles from our planet, it significantly affects us. For instance, powerful coronal mass ejections (CMEs) can directly impact the upper layers of our planet's atmosphere and the technology we use.