Q: What do we know about sunspots?

The sun is a huge nuclear reactor; it converts hydrogen into helium, and so gives us light and heat, and we should not survive for long without it. It  contains more than 99 per cent of the mass of the entire solar system, including the Earth and all the planets. The sun is so big that the energy generated at the centre takes 50 million years to reach the surface, and when it arrives it disturbs the magnetic field, and causes various surface effects that we can observe, especially sunspots.

NEVER LOOK DIRECTLY AT THE SUN – YOU WILL PERMANENTLY DAMAGE YOUR EYES. With a lens or a pair of binoculars you can make an image of the sun on a piece of white card or paper, and you may see one or two little black dots there. These are sunspots, which look dark because the surface is a bit cooler than its normal 6000 degrees. Sunspots come and go in a cycle of about eleven years – we are approaching a solar minimum now, but in five or six years’ time there will be many more spots visible.

Why should we be interested in sunspots? Because they show long-term cycles too, and seem to have some connection to our climate. Between 1645 and 1715 there were very few sunspots, and we went through a little ice age, when people held barbeques on the frozen Thames. Now we are at a thousand-year high, and the climate is warmer.

Sunspots definitely generate solar flares – vast explosions of gas from the sun that look like huge flames shooting out. These are often visible in photographs taken during a solar eclipse, when the bright disc of the sun is hidden behind the moon. Big solar flares catapult high-energy electrons and radiation far into space, and so cause magnetic disturbances on Earth – they give us enhanced northern lights, and they can disrupt communications satellites and even power grids in Canada and other northern countries.

The latest scientific investigation of sunspots and solar flares is being carried out be RHESSI, the Ramaty High-Energy Solar Spectroscopic Imager, which was launched by NASA three years ago and is in orbit 600 kilometres above the Earth, pointing steadily at the centre of the sun. It has taken thousands of x-ray photographs, and observed tens of thousands of mini-flares, and has already told us a lot about our spotty old sun.