Earth at the Mercy of a Restless Sun

February 3, 2010
UK Times

On January 19 a huge blast of light and energy erupted from the surface of the Sun, the equivalent of millions of atomic bombs being detonated. This event, called an M-class solar flare, was followed quickly by four more bursts of increasing magnitude from the same source — a sunspot.

Solar flares are so powerful that they can wreak havoc with electricity grids on Earth and scramble GPS equipment. Some have further suggested that the Sun’s activity can affect the world’s climate. These recent flares herald the beginning of an increase in solar activity that is due to peak in the summer of 2013 as part of solar cycle number 24.

The solar cycle is a pattern that occurs as the Sun’s magnetic field flips over, reversing its magnetic poles. The Sun consists of liquid plasma which spins faster around its equator than at its poles, causing the magnetic field to get “squashed up”. It’s a bit like the isobars that you see on weather maps — the closer the bars are squashed together, the higher the winds. At various points the magnetic field gets pinched, causing a sunspot to appear and a burst of magnetic activity. The increased magnetism reduces the temperature, which, in turn, leads to a reduction of light emitted, making the Sun look darker at these points.

Sunspots were first observed in Ancient China, when desert storms filtered the Sun’s glare enough for people to see the black spots on its surface. But it was not until 1843 that Heinrich Schwabe noted the cyclic activity, after making observations of the Sun for two decades. Using detailed records that had been kept of previous sunspots, astronomers were then able to trace activity back to 1755, which is traditionally called solar cycle number 1. Each new cycle begins when the sunspot activity is at its minimum.

The different rates of rotation of the magnetised plasma on the surface of the Sun are like turning cogs which return to their starting point every 11 years. But because the Sun is a fluid rather than a solid body, this cycle is open to variations. Sometimes it is as short as nine years. The last solar cycle was actually one of the longest, lasting for more than 12 and a half years. Some experts were so worried by the late appearance of solar cycle 24 that they feared it might not happen.

Given that the Sun’s variation can cause a difference of 1.4 watts for every square metre on Earth, studying solar activity could be very important in understanding our planet’s changing climate. So on February 9, Nasa is planning to launch the Solar Dynamics Observatory, to collect unprecedented data on what is happening in the Sun.

The new observatory will provide images every 10 seconds for five years, giving an almost continuous view of the Sun’s activity. To keep in contact with the ground station in New Mexico while maintaining an uninterrupted view of the Sun, its orbit has been plotted to trace an unusual figure of eight in the sky. The data that the observatory will send back to Earth is the equivalent of downloading half a million songs a day from iTunes.

With so many telescopes pointing at stars in the distant recesses of the Universe, it’s odd that only now will we obtain a detailed view of our nearest star — the one that we orbit every 365 days.

http://www.timesonline.co.uk/tol/news/science/article7012487.ece