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What's the sun up to?

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Ken Tapping, August 12, 2009

In the sky this week...

> Saturn lies low in the Southwest after sunset, just as Jupiter is rising in the East.

> Mars rises just after midnight, and Venus rises in the early hours.

> The Moon will reach Last Quarter on the 13th.

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For about a year, we and others around the world who monitor the Sun's behaviour have been awaiting the start of the next solar activity cycle. We've had some hiccups of activity, but as yet the new cycle is not yet under way. The Sun is definitely up to something, but we don't know what. That's interesting, but why should we care?

Firstly, solar energy is what drives our environment, and with the exception of nuclear power, all the energy we use is supplied by the Sun, either today, or captured in the past, in "fossil fuels". We tend to think of the Sun as a constant factor in our lives. However, it isn't. Its energy output varies; when activity is high, the Sun gets very slightly brighter, and when activity is low, it gets a little fainter. In addition, solar activity costs us billions of dollars a year by degrading and damaging our technologies and infrastructure. That's why in Canada and around the world we are monitoring the Sun's behaviour very carefully, in many different ways. That brings us back to what is happening now.

It's best to start the story back in the 1600's, when Galileo, Scheiner and others discovered sunspots, and as time passed, found that the sunspots come and go in a rhythm. Sometimes there were many sunspots, and several years later there were few or none, and then, a few years after, there were many again. This "sunspot cycle" lasts between 10 and 13 years, with an average duration of 11 years. Now we know that this coming and going of sunspots is part of a deeper rhythm, associated with processes taking place deep inside the Sun. Moreover, this rhythm does not just manifest itself in changing the number of sunspots, it also appears in the levels of ultraviolet and other emissions, and even in small changes in the Sun's energy output. Scientists in Canada and around the world are working to understand how the Sun does these things. However, we have a long way to go.

We have now been counting sunspots for more than 300 years. During that time there has been a trend for the number of sunspots seen at the activity maximum to increase, although there have been occasional falls for a cycle or two. In the late 1600's there was a period of low activity, known as the Maunder Minimum, when sunspots were rare. This was associated with a cooling of the Earth's climate. Using ice cores and tree rings we can track the terrestrial impact of solar activity back further in time, and see other periods where the solar activity cycle sank to low levels for a while.

Is one of those periods starting now? We cannot be sure of that. The latest prediction is that the next solar activity cycle will start before the end of this year. However, solar forecasting is still a very iffy business. The Sun is about halfway though a ten billion-year lifetime. We have been counting sunspots for only 300 years or so, and monitoring the Sun in detail for just more than 60 years. It would be naïve to assume we understand all the nuances of the Sun's behaviour, or know all the weird things it might decide to do. All we can do is keep monitoring and keep working on the problem.