Solar cycles track the max
AS we enter the third decade of the 21st century, the sun is beginning the build-up to its next “solar maximum” around 2025 — the peak in its activity that takes place, on average, about every 11 years. Many astronomers predict a relatively weak maximum, but a recent study has suggested that it will be quite strong — and I find their work to be quite convincing.
We have known about the 11-year cycle since its discovery by Samuel Schwabe in 1843. It is mainly tracked by noting the number of sunspots. However, a variability in their number had been noted decades earlier, and we number the 11-year cycles from the one that peaked in 1761. Cycle 25 is beginning now.
Sunspots are magnetic disturbances that result in the temperature of the outer layer of the sun, called the photosphere, dropping by about 2000 degrees from its normal value of about 5500 Celsius.
Other types of solar activity are flares, which are releases of huge amounts of magnetic energy, and prominences, which are relatively cool gaseous features that are attached to the photosphere and sometimes form loops. There are also coronal mass ejections, which send huge bursts of charged particles into space.
Strictly speaking, a full solar cycle is about 22 years long, because sunspots typically occur in pairs or groups, whose magnetic polarity reverses from one cycle to the next. During one 11-year cycle, the eastern sunspot of a pair is a magnetic north pole, and in the next cycle the eastern one will be a south pole.
The maxima vary considerably in intensity. In particular, there has been a noticeable drop since the very high maximum of 1979, with the number of sunspots at the 2014 maximum being only half that of 1979.
Some astronomers predict that the trend will continue, and that the maximum around the middle of the present decade will be still lower. It has even been suggested that we may be heading into a period of many decades of very low activity. We know that this has taken place before. There was exceptionally low sunspot activity between about 1645 and 1715.
However, we may, instead, be in for a big maximum.
In a research paper published recently, a team of astronomers led by solar physicist Scott McIntosh has analysed the so-called “termination events”, which mark the end of the 11-year cycles. Each one finishes with the last few spots of the cycle being more concentrated near the equator.
Sunspot records had already suggested that a short-duration solar cycle indicates that the next maximum will tend to be high, but exact determination of the time of the end of a particular cycle is difficult.
McIntosh and others applied more detailed techniques to determine these points in time. Their work involved observations of bright points of ultraviolet light that progressively appear at lower latitudes during each of the long 22-year cycles, and reveal patterns in the sun’s magnetic field. This has given a more exact definition of the termination of each 11-year cycle. The study has pointed to a clearer connection between the duration of one solar cycle (termination to termination) and the intensity of the next one.
It seems that termination of Cycle 24 has recently taken place, so the duration between the last two terminations has been less than 10 years. The authors therefore predict that the next maximum will be considerably higher than that of 2014, going against general opinion.
An intense peak in solar activity is bad for several reasons. The resulting geomagnetic storms can cause problems with the electronics in orbiting satellites, disrupt communications, and even trigger electricity outages, such as the one that blacked out parts of the US and Canada in 1989.
However, it would have a rather beautiful effect on our night sky, producing more auroral displays. Tasmania is famous for being the best place in Australia to see these!
We shall have to wait and see, but the wait may not be long. As astronomers watch the sun over the next year or two, it should be possible to see which prediction is more likely to be correct. However, it is important to remember never to look directly at the sun, and especially not through binoculars and telescopes, because eye damage will result. Studies of the sun must be made using the correct equipment and expertise.