Counting sunspots over time helps in knowing the activity of our star but the two indices used by scientists disagree on dates prior to 1885. Now an international team of researchers has tried to standardise the historical results and has discovered that, contrary to what one may think, the solar activity of our times is very similar to that of other times, such as the Enlightenment.
Scientists have been counting sunspots since 1610 with small telescopes. Thus it has been verified that the Sun's activity increases every eleven years, according to the interval in the growth of the number of darker and colder spots in comparison with the rest of its surface. The more spots that appear, the more luminous the surrounding areas are, and our star shines brighter.
Nonetheless, the eleven-year cycles do not always have the same intensity. The more intense peaks of the Sun's luminosity were produced in the 20th century, which experts have called the 'modern maximum'. However, an international team of scientists has reviewed the historical data and has verified that there were also elevated values in other periods.
"It has been a huge surprise to observe that in the 18th century the levels of the Sun's activity were practically the same as they are now," points out José M. Vaquero, researcher at the University of Extremadura (Spain) and co-author of the research, a review of the number of sunspots recorded in the last 400 years.
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