How bad can sun behave?

Photo: Contributed

We depend on the sun. Without it our world would be very cold, dark, and lifeless. It provides our light and heat. Since we are so dependent on it, we are also vulnerable to any fickle behaviour it might get up to.

We are familiar with its more or less regular sunspot cycle, where the level of magnetic activity and consequently the number of sunspots rises and falls over a period of 10-13 years. However, at various times in the past, such as the period 1645-1715, its behaviour changed; its magnetic activity decreased dramatically, sunspots became rare and our star got slightly dimmer, resulting in a cooling climate and weather cold enough for the River Thames in London to freeze over. This is very unusual. Then, around 1715 the cycle restarted and we returned to the behaviour pattern we are familiar with today. 

Solar magnetic activity drives solar storms, great clouds of ionized gas thrown off by the sun (better referred to as coronal mass ejections), and blasts of high energy particles and radiation can degrade or completely disrupt our technical infrastructure. So the big question is whether what we have seen the sun do since we started watching it is typical, or can it get worse.

The sun is 4.5 billion years old and about halfway through its life. What we have seen over a few hundred years and in more detail over a few decades is not really representative. However, as we exploit our planet's resources more completely, and become more and more dependent on technical infrastructure, it becomes increasingly important that we find out.

The sun is a fairly average yellow dwarf star, powered by nuclear fusion – the conversion of hydrogen into helium. Solar rotation and complex flows of extremely hot gas and magnetic fields inside the sun generate enormous electrical currents and in the process generate more magnetic fields. This process is known as the solar dynamo. These magnetic fields permeate the interior of the sun and erupt through the surface and out into space. Patches of strong magnetic field on the solar surface are known as active regions.

In some places the magnetic fields are so strong they interfere with the outward flow of energy, creating cooler patches, known as sunspots. The magnetic fields are the troublemakers. They can change the efficiency with which the sun radiates energy into space and, being elastic, enormous amounts of energy can be stored in them through stretching and twisting. Energy stored over days can be released in seconds, providing the energy for solar flares and coronal mass ejections. We need to know whether the patterns of solar behaviour we know of are typical. Can it get worse, or better? One approach being investigated is to look at sun-like stars. 

The sun is a fairly average yellow dwarf star, and our neighbourhood in the Milky Way contains a fair number of similar stars, some older, some younger, and some of these stars have been monitored for many years. Some of them show similar magnetic activity cycles, and some don't. Maybe these stars are doing what the sun did in the late 17th Century. Interestingly though, it looks as though in general those sun-like stars are more magnetically active than ours has been. 

The engine driving the magnetic activity is driven by the sun's rotation. For some reason, as yet unknown, the sun is rotating more slowly than those other sun-like stars, which would explain why they are more active, but it does not really help us with the fundamental question, namely how badly can the sun behave. We need to know.

• Venus still dominates the western sky after sunset, but is slowly sinking back into the sunset glow.
• Mars, Jupiter and Saturn lie low in the southeast before dawn. Mars is to the left; Jupiter and Saturn lie close together.
• The moon will reach last quarter on the 14th.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.