A scientific experiment of 315 years

How sunspot counting unites the past and the future of science

The most arrogant astronomer of Switzerland in the middle of the 20th century was Max Valdmayer , a specialist in solar physics . After his retirement in 1980, his colleagues were so relieved that they almost sent the initiative, which he led as director of the Zurich Observatory. Waldmayer was responsible for the practice, dating back to the time of Galileo, and remaining one of the longest scientific practices in history: the counting of sunspots .

Zurich Observatory was the world capital for calculating sunspots: cold dark areas on the surface of the Sun, in which the circulation of internal heat is suppressed by magnetic fields. Since the XIX century, astronomers associated sunspots with solar flares.able to disrupt the course of life on Earth. Today, scientists know that the spots mark areas that create colossal electromagnetic fields that can interfere in the work of everything, from the global positioning system and electrical networks to the chemical composition of the atmosphere.

What repelled potential followers of Valdmeier was his hostility toward methods that differed from his own. In the space age, he insisted on the manual method of calculating spots using the Fraunhofer refractor , named after the inventor of the XVIII century, and installed by the first director of the Zurich Observatory, Rudolf Wolf in 1849. After leaving Valdmeyer, his assistant, taking advantage of the legacy uncertainty, removed the telescope Fraunhofer in his garden. Automatic observation and tracking of the Sun from satellites was an obvious improvement, as well as less subjective than the narrowed gaze of a person.

But, despite all the hostility towards Waldmayer, his method has been preserved. Spots appear cyclically. Their number has steadily increased for about 11 years, followed by about 11 years of decrease. Waldmayer realized that interpretation cannot be customized due to the inherent slowness of the cycle. “The process is not to be dispersed,” says astronomer Frederick Klett, director of the Center for the Analysis of Solar Influence Data at the Royal Observatory of Belgium. "To understand the Sun, you need to keep records of cycles for long periods of time."

And the best way to maintain data continuity, Klett explains, is to use the observation method that connects the past with the future. Unlike most modern science, which keeps up with technological developments, the human brain and the eye remain the most stable device for detecting changes in the star that gives us all life.

“Modern technologies and equipment are very capable of many things, but these technologies have existed for only a few solar cycles in a row, so they do not show changes in cycles over the centuries,” says Klett, superintendent of the global stain calculation procedure that Wolf started in Zurich, now famous as International sunspot number or Wolf number. Under the supervision of Klett, defects are still considered manually. "Considering them by sight, we can connect what we see today with what we saw in the distant past."

This is an amazing story, says Klett. One of the most long-lived scientific methods is a simple observation. "This is a long, systematic evolution of information gathering that led to an understanding of the phenomenon of sunspots, and the cherry on the cake is an opportunity to predict the future."


Works - do not touch: the Fraunhofer refractor, named after its inventor of the 18th century, was used by specialists in solar physics to calculate spots for most of the 20th century.

Spot observations began earlier than modern astronomy, for at least three millennia. Since the Sun was the central object of several ancient religions, any blemishes were considered a significant phenomenon. For the ancient Africans from the banks of the Zambezi, the sunspots were the dirt that the jealous Moon slapped the face of the sun. The ancient Chinese considered stains to be the building blocks of a flying palace, or even brush strokes defining the character of the king. Virgil used a more practical approach, warning "in his Georgics ":

If the spots start to interfere with golden fire,
everything - you see - then boils at the same time the wind
and the clouds

Galileo studied the spots more scientifically, and considered them useful marks for calibration in his studies of the solar disk. From careful observations in the telescope of the daily changes in their appearance, he correctly decided that the Sun was spherical and rotated around its axis, bearing changing defects. But from his point of view, the spots were random. It left a lot of room for imagination. The philosopher Rene Descartes believed that the spots were oceans of prehistoric foam. Astronomer William Herschel believed that these were passages to a dark sunflower world where people live under the bright shell of a star.

However, there was one amateur astronomer who simply had enough observations of the sky and records about everything he saw. Heinrich shvabeworking as a pharmacist, he began to observe the Sun in 1826, and he constantly engaged in this work for more than 300 days a year for forty years. Initially, he was looking for undiscovered planets inside the orbit of Mercury. Finding nothing definite, he gradually took up observation of the mottled surface of the sun.

By 1844, having counted tens of thousands of spots, Schwabe was convinced that spotting has a cycle: the number of spots increased and decreased every 10 years. He had no explanation for this, but he decided that others might learn something useful from his observations, so he published a one-page note in the journal Astronomische Nachrichten. His work was read by Rudolf Wolf, a 30-year-old director of the Bern Observatory. When Wolf became director of the Zurich Observatory in 1864, he decided to choose the sunspot cycle as a topic for his research.

Wolf did not satisfy the calculations only for the passage of time. To establish the existence of the cycle and measure it correctly, he wisely decided to collect past data - starting with Schwabe - and integrate them into his own daily observations.

The problem was that the numbers did not match. The number did not coincide even with the calculations for one day, which were carried out thousands of times from 1849 to 1868, until the last calculation of Shvabe. The Fraunhofer telescope was much more powerful than the old Shvabe instrument, and it was obvious that many of the Schwabe stains were actually clusters. To compensate for this, Wolf made two important decisions. The first is to reconsider our own calculations - in fact, the relative activity of the spots was really important. The second solution was to establish the relationship between the number of spots counted by him and Schwab, when their observations took place on the same day. He obtained the coefficient, called it k, and it was a multiplier that could be applied to the old observations of Schwabe until 1849, statistically combining them with the new Wolf data.

The coefficient made possible something even more interesting. Thanks to a multitude of simultaneous observations, Wolf was able to use the old Schwabe data to derive the coefficients k for other scientists, and reliably extended his data on the number of spots until 1700. Then Wolf created a whole network of spot counters on the continent, and their daily calculations, varying from zero to a couple of hundred, became one of the most reliable data sets in astronomy.

The data showed that Shvabe was right about the sunspot cycle, but not about its duration. At first, Wolf recounted this period of 11 years, and decided that he discovered his reason: Jupiter needs 11 years to go around the Sun in orbit. However, the more cycles he collected, the less reliable this correlation looked. Some cycles lasted for 14 years. Others of 9. Since the orbital period of Jupiter has not changed, the scientist had to admit defeat.

He continued to calculate in the confidence that someone, having enough data, would be able to uncover the mechanism for the appearance of sunspots. He believed until his death in 1893. By that time, his assistant Alfred Wolfer had been working on spot calculation with him for 17 years. Their coefficient k ensured a smooth transition of observations to other directors of the Zurich Observatory, right up to the arrogant Valdmeier, who developed an evolutionary classification of sunspots and a method for predicting geomagnetic storms, which seriously advanced solar science.


The stunning image of a sunspot indicates the place where magnetism has suppressed the movement of heat into the sun, solar convection. Sunspots mark areas from which colossal flares erupt, affecting GPS and the electrical networks of the Earth.

So why are periods of dark spots replaced by periods of pure Sun? “In truth, we still don’t know exactly what the frequency depends on,” admits Klett. Even after 315 years of data collection, the sunspot cycle mechanism has yet to be fully elucidated.

However, since the days of Shvabe, serious progress has been made, especially in the field of the influence of solar flares. In 1859, two amateur astronomers on the Wolf observation network noticed two bright flashes inside a cluster of spots. In the following days, the telegraph was disrupted, and the northern lights were observed throughout Europe . Several such episodes convinced scientists about the connection of these phenomena, the explanation of which came in 1908, when astronomer George Ellery Haleused the spectroscope to determine the magnetic nature of sunspots (magnetism slightly affects the color spectrum). The dark defects of the Sun could finally be understood. They were not prehistoric foam or signs of a Sun population, but areas in which magnetism suppressed the movement of heat into the Sun, in a process known as solar convection.

Today, thanks to solar physics, we know that the cycles of the spots are controlled by the rotational motion of the plasma inside the rotating Sun. Since the plasma is electrically charged, and the plasma layers rotate at different speeds, the sphere of the Sun behaves like a dynamo, producing electromagnetic fields thousands of times stronger than the polar magnetism of the Earth. The circulation of the plasma that creates the solar dynamo is modeled on supercomputers. For centuries, collected data on sunspots helped scientists refine and test these models, running simulations, observing which models most closely resemble different periodicity of successive cycles. The better models become, the better we will understand the sunspot cycle.

The need for counting sunspots, Klett explains, only increased when moving from telegraphs to satellites. “The number of spots helps to establish a trend over the next months and years to predict the frequency and strength of disturbances,” he says. The Royal Observatory of Belgium constantly receives data requests from telecommunications and energy companies. Commercial airlines are also dependent on the trends of sunspots, because solar magnetism affects the speed of passage of radio waves in the ionosphere and distorts the GPS coordinates. If the sunny weather is approaching a storm, the pilots will focus on other navigation tools.

Between the life of the earth and sunspots, less confirmed correlations are also derived. Medical researchers are trying to find a connection between solar magnetism and cancer. Economists look at the relationship between solar cycles and agriculture. Climatologists want to know whether the glacial periods are not caused by periods of “great minima” - when there are almost no sunspots on the Sun - as happened in the 18th century. The paintings of that period depict people skating on the Thames and Venice.

Progress in climatology is particularly interesting. It is known that the radiation of the Sun changes the chemical composition of the upper layers of the atmosphere, and sunspots modulate the intensity of various wavelengths - from infrared to X-rays - bombard our planet. By associating the number of spots with changes in the solar spectrum, climatologists will soon be able to determine the spectral image of the Sun during the great minimum of the 18th century.

Before such application of data, Wolf would never have thought of it - it will be a lesson for other Wolfs of the present and the future: the solution of one of the most important problems in modern science - global climate change - will depend on data collected long before it became known. “I think this is the essence of scientific research, during which you are observing a new phenomenon that you cannot understand,” says Klett. - It looks like the opening of a new territory. You know that you will receive new knowledge, even if they do not come from the directions you are expecting. ”

The explanation of the sunspot cycle will be the final confirmation of the centuries-old Wolf Gambit. But as a sunspot supervisor, Klett gleefully meets another breakthrough: he recently contacted a man who inherited Wolf's tools from the treacherous assistant Valdmeier. Observations with the help of the old Fraunhofer telescope again contribute to the international calculation of sunspots.

Delight Klett is not related to sentiment, but only notes the main role of Wolf in turning the counting of spots into a consistent procedure. “I was able to determine the k-factor of this telescope,” he says. - It ideally coincides with what Wolff defined in the 19th century - and this, if we consider that today it’s not Wolfe who does the calculation. Coincidence k is a sign that the brain-eye system has not changed in the last couple of centuries. ”

And if the last couple of centuries is a good indicator, then simple observations will have value for a very long time. The calculation of sunspots can be a model for any research requiring long-term data collection, such as subtle changes in the behavior of an ancient star thousands of years before becoming supernovae. Compared with the study of supernovae, which requires time of tens or hundreds of generations, the calculation of sunspots seems very fast.

Such a long-term experiment will become an epic task. It will depend on the statistical ingenuity worthy of Wolf, and the stubborn traditionalism worthy of Voldmayer. But in order to reach the highest potential, you need such a calm mindset as that of Schwabe, who did not have to know what exactly they would find in his data - merit was also in mere observation of the phenomenon of nature.