What’s happening to the Sun?

An Image of the Sun

An Image of the Sun taken by Peter Woolliams. Sunspots are just visible in the northern hemisphere. Click for larger image.

Fascinating news this week about a prediction that the Sun is about emit less light over the next 50 years than it has for previous 400 years. This is an amazing prediction because actually we know very little about the internal dynamics of the Sun. What we do know about – and have known about for hundreds of years – are sunspots. These are regions of the surface of the Sun which are slightly cooler than the rest of the surface and so appear slightly dark – you can see one or two such spots in the image at the head of the article. People who counted the sunspots noticed that the number of them visible on the Sun varied on an 11-year cycle – falling to zero or nearly zero in between highly variable maxima.

Early Sunspot Numbers

Sunspot numbers from 1600 to 2010. Notice the period from 1650 to 1700 with almost no sunspots. Click for larger image.

And observations of the Sun from satellites show that the output of light energy from Sun also changes very slightly in synch with the sunspot numbers.

composite-total-solar-irradiance

Composite total solar irradiance - how the brightness of the Sun has changed over the last 35 years. Notice the 11 year cycle and that the last minimum was deeper than previous ones. Click to enlarge.

The recent minima in sunspot numbers included a year – 2010 – with almost no sunspots, and corresponded to a slight fall in solar output. Such a long sunspot-free period had not been seen since 1913. Sunspot numbers look to be recovering and heading towards a maximum which would be low, but within the previously experienced variability of sunspot numbers. The current news story is based around a prediction that the next cycle of sunspots will not be normal – that in fact we may now enter a period of many decades with no sunspots whatsoever. This is an amazing prediction and if correct would represent the first significant prediction ever made about the internal behaviour of the Sun.

A period of low sunspot numbers did occur from 1650 to 1700 – just as people began to count to sunspots. The period – known as the Maunder Minimum – lasted for around 50 years and corresponded to a period known in Western Europe as the little ice age.

Is the prediction correct? Well the prediction was made at a conference and not in a peer-reviewed journal so it may be that there is some flaw in the researchers arguments, but ultimately we just have to wait and see. Fortunately we are now in a position to study the Sun in some detail so if something unusual happens we should be able to track it.

Significantly, the prediction of a fall in sunspot numbers implies a fall in solar output, which in turn implies that the surface temperature of the Earth will cool. It looks like the coming decades will be just as interesting for climate research as the previous decades have been.

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