Sunspot sketches based on observations, drawn by Kepler in 1607HAYAKAWA, H. et al. Astrophysical Journal Letters. 2024
In 1607, German astronomer and mathematician Johannes Kepler (1571–1630) created three drawings of a group of sunspots using a device called a camera obscura—a small hole in a wall that he used to project an image of the Sun onto a sheet of paper. At the time, he believed he was seeing the passage of Mercury across the Sun, but the phenomenon was later reclassified as sunspots—areas on the Sun’s surface that appear darker due to intense magnetic activity. Sunspots go through cycles of frequency and distribution that affect solar radiation and space weather. An international team led by researchers from Nagoya University in Japan examined Kepler’s sketches, compared them with current data, and determined that they were drawn on May 28, 1607. With the naked eye, Kepler located the spots at a low latitude, east of the central meridian, in contrast to drawings from 1610 onwards, which were based on telescope observations and show groups of sunspots at higher latitudes. The discrepancy suggests that Kepler’s sunspot group was not part of the beginning of a solar cycle, but the end of a previous cycle, which helps explain the regularity of these phenomena. “This is the oldest sunspot sketch ever made with an instrumental observation,” Hisashi Hayakawa, the study’s lead author, told EurekAlert (Astrophysical Journal Letters and EurekAlert, July 25).
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