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German astronomer Johannes Kepler made sketches of sunspots in 1607 from his observations of the sun’s surface – and centuries later, the pioneering drawings are helping scientists solve the mystery of the sun.
Although everything in the solar system revolves around the sun, scientists still do not know many of the stars’ secrets.
However, studying the sun’s variability over time, including the solar cycle, could answer some of the longest-standing questions about the fire orbit and how it changes.
Some of these questions relate to the activity of the sun in the 17th century, a crucial time for the study of the sun.
Astronomers observed sunspots with telescopes for the first time in 1610. At the same time, the sun was making an unusual transition into an extended period of weak activity. And Kepler’s long, indifferent sketches, overlooked because they were drawings rather than telescopic observations, could provide vital historical insights.
A new study that recreates the circumstances in which Kepler made his drawings appeared on July 25 in The Astrophysical Journal Letters.
“Kepler set many historical benchmarks in astronomy and physics in the 17th century, leaving its legacy even in the space age,” said lead study author Hisashi Hayakawa, assistant professor at the Space Environmental Research Institute -Nagoya University World, in a statement.
“Here, we add to that by showing that Kepler’s sunspot records predated the telescopic sunspot records from 1610 by several years. His solar sketches are a testament to his scientific prowess and perseverance in the face of technological limitations.”
Subtle activity of the sun
The sun has an 11 year cycle of waxing and waning activity, known as the solar cycle. Currently, scientists believe that the sun is reaching or approaching solar maximum, the annual peak of its activity for the current solar cycle, known as Solar Cycle 25.
A solar maximum is usually associated with an increase in the number of sunspots visible on the sun’s surface. These dark regions, some of which can reach the size of Earth or larger, are driven by the sun’s strong and ever-shifting magnetic fields.
Today, scientists track the sun’s activity using data from ground- and space-based observatories, magnetic maps of the sun’s surface, and ultraviolet observations of the sun’s outer atmosphere.
But trying to notice the sun hundreds of years ago was difficult.
Sunspots were observed with the naked eye through fog, haze, wildfire smoke, or near sunrise or sunset when the atmosphere helped reduce the brightness of the sun, said Mark Miesch, a research scientist at the Administration National Oceanic and Atmospheric Space Weather Forecast in Boulder, Colorado. Miesch was not involved in the new research.
Kepler used an apparatus called a camera obscura, which used a small hole in the wall of the instrument to project the image of the sun onto a sheet of paper and sketched the features he saw. Kepler mistakenly believed that he had observed Mercury orbiting the sun in May 1607, but retracted his report 11 years later and concluded that he had observed a group of sunspots.
“Since this record was not a telescopic observation, it was only discussed in the context of the history of science and was not used for quantitative analyzes of the solar cycles in the 17th century,” Hayakawa said.
“But this is the oldest sunspot sketch ever made with instrumental observation and projection. We realized that this sunspot drawing should be able to tell us the position of the sunspot and show the phase of the solar cycle in 1607 as long as we managed to reduce the observation point and time and the tilt of the coordinates Re-creating holograms – meaning the sites. features on the surface of the Sun — at that time.”
Extreme solar minimum
Sunspots aren’t the only way scientists can understand changes in the sun. Variations within the sun’s magnetic field control the movement of high-energy particles, known as cosmic rays, through space, Miesch said.
When cosmic rays hit the Earth’s atmosphere, they can change its chemistry, including the balance of carbon.
“Over time, this carbon has been incorporated into plants and animals, even ourselves,” Miesch said. “Tree rings provide a unique opportunity to track carbon change from year to year. Some rings in ancient trees can be traced back thousands of years. Isotopes of carbon and other elements can also be traced through air bubbles trapped in glacial ice cores.”
The carbon isotopes trapped in tree rings and ice cores have been used to contextualize ancient sunspot observations and expand our understanding of solar activity before sunspot observations occurred, Miesch said.
Such data was used to help astronomers understand the Maunder Minimum, a period of extremely weak and unusual solar cycles between 1645 and 1715. During this so-called great solar minimum, sunspots almost disappeared, and only the small number observed in the. southern solar hemisphere. The mechanism behind the solar minimum is still debated by astronomers today, especially when they are trying to work out when and if it might happen in the next few centuries.
But astronomers agree that the sun’s activity pattern gradually shifted from regular cycles to a grand minimum.
Previous tree ring analysis suggested that a short solar cycle, Solar Cycle minus 14, was only about five years long resulting in a very long solar cycle of 16 years, known as Solar Cycle minus 13.
“If true, this would be interesting indeed,” Hayakawa said. “However, another tree-ring reconstruction showed a sequence of solar cycles with normal periods (11 years). Then, which reconstruction should we trust? It is extremely important to check these reconstructions with independent — preferably observational — records.”
So he turned to Kepler’s sketches.
Hayakawa and his colleagues translated Kepler’s original report, written in Latin, to understand the exact orientation of his sunspot sketches, as well as to narrow down the time range and locations in which Kepler made the observations.
Hayakawa then visited sites in Prague, including Kepler’s residence at the French Crown and the workshop of the court mechanic Justus Burgi, to better understand the topography from which Kepler saw the sunspots.
Modern data tools enabled Hayakawa and his colleagues to calculate the inclination of the sunspot and determine its position on the sun. They also applied Spörer’s law, first observed by the English amateur astronomer Richard Christopher Carrington but further developed by the German astronomer Gustav Spörer, which described the migration of sunspots from higher to lower latitudes during a cycle solar.
The research team determined that the sunspot group seen by Kepler belonged to the tail end of Solar System minus 14 rather than the beginning of Solar System minus 13.
The results support the idea that the Solar Cycle regularly lasted minus 13 rather than 11 years rather than 16 years. The researchers were also able to estimate that Solar Cycle minus 13 probably started between 1607 and 1610.
“This shows a typical transition from the previous solar cycle to the following one, according to Spörer’s law,” study co-author Thomas Teague, an observer at the Solar Impact Data Analysis Center at the Royal Observatory of Belgium, said in a statement.
Since the longest solar cycle ever recorded within the last three centuries lasted 14 years, it’s time to find another scientific precursor to the Maunder Minimum, Hayakawa said.
Kepler’s lasting legacy
There is still much to learn from historical figures like Kepler, said study co-author Sabrina Bechet, a researcher at the Royal Observatory of Belgium.
“As one of my colleagues told me, it’s fascinating to see the legacy records of historical figures communicating vital scientific implications to modern scientists even centuries later,” Bechet said. “In the case of Kepler, we are standing on the shoulders of a scientific giant.”
Kepler’s sketches are helping to inform ongoing debates about the solar cycles that led to the Maunder Minimum, which could also help astronomers model the conditions leading up to the event, Hayakawa said.
“By situating Kepler’s findings within broader reconstructions of solar activity, scientists gain critical context for interpreting changes in solar behavior in this critical period that transitions from regular solar cycles to the grand solar minimum,” a he said.
Miesch called the new study “an amazing piece of work” and an example of detective work that yields new insights from historical records.
“The long history of observations of the sun provides a link through the ages with generations of astronomers whose admiration and curiosity about the sun progressed from superstition to scientific scrutiny to understanding. It is inspiring to see that the astronomers of the past continue to contribute to scientific discovery. And their efforts are now more important than they could have ever imagined, as our technological society becomes more vulnerable to the waxing and waning of timeless solar activity.”
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