The SOHO observatory captures the first sunspot of the new solar cycle. Image: ESA/NASA

The new year welcomed the beginning of a new solar cycle, with the first sunspot of Cycle 24 observed on 4th January.

The previous solar cycle, Cycle 23, has been winding down for several years, with barely any sunspot activity at all. Cycle 24 has been slow getting started compared to the average over the last few cycles. Towards the end of 2007, a modest patch of magnetism was spotted on the Sun's eastern limb, although no sunspot was accompanying it at this time. New solar cycles always begin with a high-latitude, reversed polarity sunspot. High latitude refers to the Sun's grid of latitude and longitude; old sunspots congregate near the Sun's equator and new sunspots appear higher, at around 25-30 degrees latitude. Reversed polarity means a sunspot with opposite magnetic polarity compared to sunspots from the previous solar cycle, such as the one detected on the 4 January this year. However, Solar Cycle 23 has not yet ended, and it may run concurrently with the new cycle for up to a year while sunspots from the old cycle become less numerous.

Sunspots appear in pairs and are observed as darker, cooler patches on the Sun's surface. They are formed when magnetic fields born deep within the Sun break out to the surface and loop over; the feet of the two ends of the loop mark the location of the sunspots where the field lines cross the surface. Around each sunspot pair is a zone of active magnetic activity, which can give rise to several generations of sunspots. The sunspots drift towards the equator as the Sun rotates, winding up the magnetic field lines at a rate of 25 days at the equator and 35 days at the poles. It's thought that Cycle 23 was so slow because the magnetic activity didn't descend to the equator as quickly as usual, prolonging the cycle and possibly leading to a slow starting Cycle 24.

It is not yet certain how active Cycle 24 will be, but it is thought that the sooner the new cycle takes over the currently waning cycle, the more likely it will be a strong season with many sunspots and solar storms. During a solar storm, highly charged material ejected from the Sun may head towards the Earth, where it can cause disruptions to power grids, telecommunications, GPS systems and even mobile phones. The solar storms will coincide with the solar maximum, which for Cycle 24 is likely to be around 2011 or 2012.

For more information on the new solar cycle, and what this means for the Sun, see the latest March 2008 issue of Astronomy Now.