Spot of bother: have we been getting solar activity wrong?

For 400 years sunspot numbers have told us what the sun is up to. But wrinkles in the record have left solar scientists scratching their heads, until now.

EVERY lunchtime, Gustav Holmberg leaves his desk at Lund University in Sweden to take part in a scientific ritual that stretches back to Galileo’s time.

Back at his flat, the historian of science sets up a modest telescope and, taking due care not to burn his eyes, points it directly at the sun. He spends 5 minutes or so counting, and uploads a number to a server in Belgium. There, it is automatically combined with similar numbers from some 90 other observers around the globe, two-thirds of them amateurs like himself.

Satellite engineers use this number, updated daily, to predict how the sun’s future activity will affect their spacecraft. Climate scientists use it to pick out the sun’s long-term effects on Earth’s climate. Electricity companies use it to anticipate solar storms that could affect their grids. It is the international sunspot number: the world’s oldest continuous data series, and one of its most important. Read more in New Scientist.