To the casual observer, the Sun may appear calm and unchanging. However, the behaviour and energy output of our nearest star varies according to a cycle that lasts 11 years or so. This behaviour has been followed by counting the number of sunspots - dark regions that appear and disappear on the visible solar "surface". The rise and fall in the number of sunspots - and the accompanying variations in solar activity - have attracted renewed attention recently as the Sun approaches a peak in its 11-year cycle. This interest has also been fuelled by spectacular images from spacecraft such as the Solar and Heliospheric Observatory (SOHO).
However, as we become ever more reliant on space-based technology, including the global positioning system (GPS) for navigation and remote monitoring, we are also becoming more vulnerable to the major disturbances that solar activity can trigger.
In the July issue of Physics World Janet Luhmann of the University of California at Berkeley describes how space scientists are learning more about the phenomena underlying the magnetic storms and intense bursts of radiation that will bombard the Earth as the Sun reaches the most active period in the solar cycle.