Astronomers uncover the secret of the “solar clock”

The activity of our Sun has an impact on some of our systems: our satellites, our communication systems, etc. So researchers have long been trying to predict it. With more or less success. But, today, they seem to have taken a big step in this direction by revealing a “solar clock” which rings at regular times.

Solar cycles are said to be chaotic. They last an average of eleven years. But can also last a little longer or a little less. And above all, go through a maximum of activity of varying intensity. The trouble is that during and after this maximum, our Sun is sometimes at the origin of a space weather which can damage our satellites, interfere with our communications or even disrupt our electrical networks. Greater predictability would therefore be appreciated.

And precisely, by applying a mathematical technique - a Hilbert transformation - usually used for the analysis of cyclical phenomena on Earth - like the ebb and flow of the tides -, researchers from the University of Warwick (United Kingdom -) have developed a much more regular “solar clock” than they imagined possible. Based on nearly 200 years of observations of sunspots and more than 150 years of recordings of solar flares, it shows that the activity of the Sun follows a more precise calendar than traditional observations have suggested.

Better forecast space weather

“Scientists spend their lives trying to read the book of nature,” said Sandra Chapman, physicist, in a statement. Sometimes a simple new view on data brings up an order in what seemed messy. “This is confirmed in another press release, Scott McIntosh, deputy director of the National Center for Atmospheric Research (NCAR - United States):” Once you realize that sunspots are only the symptom of the cycle, not the cycle in itself, a new order arises from chaos. ”

The “solar clock” of researchers at the University of Warwick thus reveals clear transitions between calm and active periods. It also shows that extreme events preferentially occur during active periods. What finally hope for better forecasts of the solar weather and better planning of infrastructures that are sensitive to it.

Returning to studies of solar activity for 400 years, researchers have noted several errors within the two main methods of counting the dark spots that stain our star and which are the witnesses of its activity. Cycles in past centuries, and even in the 18th century during the Little Ice Age, would be equivalent to those observed in the 20th, with maximums spaced 11 years apart on average. Levels of solar activity would hardly have changed.

Concerned by the divergences in the enumeration of sunspots before 1885, set up by the two main sources, one European and the other American, an international team of researchers conducted an investigation aimed at reconstructing, as close as possible to the reality, the activity of our star during these last four centuries. The abundance of these famous dark regions (sunspot, in English) which smear the surface of the sun star indeed informs scientists about the intensity of its activity, it is in a way its acme.

The more there are, the brighter their environment, which results in a significantly brighter star. The peak of activity is reached when their population is at its highest. In this regard, astronomers have been able to verify that their average periodicity remains 11 years, with however significant variations in the abundance of spots, from one cycle to another.

The Maunder minimum, between 1645 and 1715, is a famous example to which we attribute in part the responsibility for the Little Ice Age that had struck certain regions of the northern hemisphere. The large black dots then almost deserted the Sun, which would therefore have had a significant impact on the climate of our biosphere.

Discrepancies between sources

“A good estimate of the past and present activity of the Sun, our main source of light and heat, is crucial for understanding the many phenomena that occur on Earth, comments Jos M. Vaquero (University of Extremadura, Spain), co-author of this study published in the journal Space Science Reviews, more specifically to exclude the involvement of our star in global warming. ”

In their research, the team also found that the twentieth century does not have the exclusive preserve of the strongest peaks (as in 1959). For Professor Vaquero, “it was a huge surprise to observe that during the 18th century, the levels of solar activity were practically the same as now”.

The problem the researchers encountered “is that there are two historical indices or ways of calculating solar activity and their data do not coincide when it comes to describing what happened before the 20th century” . The first, called the International Sunspot Number, was created in 1849 by the Swiss astronomer Johann Rudolph Wolf. The Royal Belgian Observatory which participates in this research (associated with Stanford University and the US National Solar Observatory) has adopted this method, like hundreds of others - including many amateurs - in the world. The second, designated Group Sunspot Number, was launched in 1998 by the Americans Douglas V. Hoyt and K.H. Schatten. “(…) The American catalog shows a lower level of solar activity than the European, notes Vaquero, which causes confusion and contradictions when the number of sunspots is used in modern research in this area. which concerns dynamo or solar forcing on the terrestrial climate system, for example. ”

The errors highlighted in the two indices could be partly corrected thanks to the data compiled in the sunspot catalogs of the observatory of the University of Valencia, for the period 1920 to 1928, and that of the observatory from Madrid, from 1876 to 1986.