It is now 19 months since I speculated that the Sun was then close to the minimum in its approximately 11-year cycle of activity. In fact, solar activity, as measured by (among other factors) the number of sunspots, has continued at a low ebb and solar experts at a recent international workshop have suggested that the minimum may not have occurred until March this year. This can only be confirmed after several further months of observation.

Certainly, the Sun's disc has been pristine and spotless over many days of late. Such was the state last Friday when observers in Russia and China were able to admire the outer regions of the Sun's atmosphere, the corona, during a total eclipse. Shaped largely by magnetic field lines, this can spill out chaotically in all directions around the disc when spots are plentiful, as during "our" eclipse in 1999. Last Friday, though, the corona stretched mainly to the east and west of the disc, taking on the much more quiescent form typical near solar minimum.

The experts offer two predictions as to how solar activity will progress. One is that there will be a rapid climb to a maximum in October 2011, perhaps at a level to rival that of 2001. The second envisages a slower climb to a lower peak in August 2012. Either way, satellites in low orbit are about to experience greater atmospheric drag, and reduced lifetimes, as the increasing solar activity energises and expands the outer layers of the Earth's atmosphere.