Renaissance astronomer Johannes Kepler’s “half-forgotten” drawings of sunspots show us more about how the cycle of solar activity works.
Kepler (1571-1630), who was born in what we now call Germany, is best known in astronomy for the formulation of the laws of planetary motion. However, his varied interests included watching sun. A new study shows that drawings of a group of sunspots in 1607 show “the end of the tail solar cycle‘ with instrumentation before the telescope was widely available in the early 17th century.
“The group’s findings … offer the key to resolving a dispute over the duration of solar cycles in the early 17th century,” Japan’s Nagoya University wrote. in the statement.
Known as the Maunder Minimum (between 1645 and 1715), this period was thought to be a period with fewer sunspots than usual, leading to colder-than-normal periods on Earth.
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Lacking a telescope, Kepler instead examined the sun with a camera obscura. The method used “a small hole in the wall to project an image of the sun onto a sheet of paper,” the statement said. At first Kepler thought he was witnessing a transit Quicksilver across the sun, but it was later clarified that it was a group of sunspots.
“This is the earliest sketch of sunspots ever made using instrumental observation and projection,” lead author Hisashi Hayakawa, an assistant professor and solar scientist at Nagoya, said in a statement. He added that the significance of Kepler’s solar drawings has been overlooked throughout the ages: “It has only been discussed in the context of the history of science and has not been used for quantitative analyzes of solar cycles.”
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Key to the scientists’ analysis was tracking how sunspots move across the solar cycle: “Their occurrence, frequency and geographic distribution appear in cycles that affect solar radiation and space weather,” the statement said. As such, they tried to narrow down at what latitude Kepler’s sunspots were observed.
The researchers say their analysis of Kepler’s drawing revealed four main things.
First, the sunspot cluster was at a lower latitude than previously thought (after accounting for the sun’s position angle from its position); related to this, future findings in the telescope showed sunspots at higher latitudes, suggesting a “typical transition” between the cycles.
The change in latitude suggests that the sunspot group was at the end of one solar cycle instead of the beginning of another, based on the latitude of the sunspots, which formulated the third finding.
Finally, Kepler’s observations may show the transition zone between solar cycles that the study established between 1607 and 1610.
While some scientists previously theorized that the Maunder Minimum arose from irregular solar cycles different from the typical 11 years, Kepler’s records showed the “regular duration” of the solar cycle he observed in 1607, the study added.
However, the finding is not without controversy: tree-ring cycles from previous studies suggested normal solar cycles in some papers and abnormal solar cycles in others.
Hayakawa urged further investigation into the matter. “It is extremely important to control them [tree rings] reconstruction with independent – preferably observational – records,” he stated.
The new study was published in The Astrophysical Journal on July 25.