We’ve all been enjoying the summer Sun, but how many of us stop to think about the dynamics of our local star? Throughout history, the Sun has been worshipped and celebrated with rituals and festivals throughout the world. And there’s good reason for celebration; sunshine gives us light and heat – vital ingredients for life on Earth.
Our seemingly unchanging star is in perpetual motion; rotating on its axis once every 27 days and moving through space on a 225 million year orbit around the centre of the Milky Way. What’s more, its surface – or ‘photosphere’ – is in constant flux.
Since the mid eighteenth century, astronomers have been researching patterns in solar activity, studying the ebb and flow of stellar events, and have discovered that our star has an 11-year cycle. During each cycle, its magnetism flips from one pole to the other. At the point of switching polarity, the Sun is at its most active; a time known as ‘solar maximum’. It’s at this point that we expect to see the photosphere peppered with sunspots (dark areas of intense magnetic activity); to observe an increase in solar flares, or ‘prominences’; and to experience a higher number of coronal mass ejections (CMEs). A CME is an immense loop of ionised plasma many times the size of our planet which breaks, sending charged particles racing through the Solar System. About 10% of CMEs smash into Earth’s atmosphere, causing spectacular displays of the Northern Lights. Unfortunately for us technology lovers, these major events occasionally cause disruption to our satellites, devastation to power grids, and can even be a danger to air passengers and astronauts aboard, or en route to, the International Space Station.
We’ve just passed the point of solar maximum, but apart from the odd solar eruption, a lack of recent activity has taken solar physicists, like Richard Harrison, head of space physics at the Rutherford Appleton Laboratory in Oxfordshire, by surprise. “If you want to see when the Sun was this inactive… you’ve got to go back about 100 years,” he says. “I’ve been a solar physicist for 30 years, and I’ve never seen anything quite like this.”
Back in the 17th century, a run of bitterly cold winters was recorded. So cold in fact, that it was dubbed the ‘mini-Ice Age’. One theory for this is that then, like now, the Sun went through a period of inactivity. Known as the Maunder Minimum (after solar astronomers Annie and Walter Maunder who studied sunspot latitudes), it was a time when London hosted Frost Fairs on the ice-covered Thames; when snow covered most of Europe; and the Baltic Sea froze over. Historical records mark a distinctive lack of sunspots at this time; this combined with the study of corresponding ice cores, showing an increase in snowfall, back up this theory.
So, will the current quiet phase in the Sun’s output lead to more cold winters now, in the 21st century? Only time will tell, but Mike Lockwood, professor of space environment physics, from the University of Reading, thinks there is a significant chance that the Sun could become increasingly quiet. “It’s an unusually rapid decline” he explains. “We estimate that within about 40 years or so there is a 10 to 20% probability that we’ll be back in Maunder Minimum conditions. It’s a very active research topic at the present time, but we do think there is a mechanism in Europe where we should expect more cold winters when solar activity is low”.
Should we worship our super star, or fear it? Perhaps there’s cause for a bit of both. The Sun is all powerful, yet unpredictable. With global warming being such a hot topic, we shouldn’t get too complacent. Sun-induced polar conditions may be upon us in the coming decades, but this will only dull the effects of climate change, which seem inevitable.
If you want to find out more about our dynamic star, visit the Solar Dynamics Observatory website at sdo.gaff.nasa.gov, or the Solar and Heliospheric Observatory at sohowww.nascom.nasa.gov. Many astronomy societies own their own solar scopes – specially adapted telescopes for viewing the Sun. Why not join your local group, summer is here and it’s a great time for studying stellar fluctuations.