Andrew spots a massive eruptive prominence

February 4, 2010

At the February 2010 meeting of Sydney City Skywatchers the guest speaker was Associate Professor Mike Wheatland from Sydney University. Mike presented “A Sunspot’s Tale”. Sunpots are regions on the Sun’s surface with strong magnetic fields, a magnetic “storm” if you like. Around sunspots intense magnetic explosions or flares can occur. How flares are actually produced is poorly understood, but they give out intense storms of X-rays.

Typically, from each active region we expect to receive many bursts of weak X-rays and fewer and fewer bursts of more and more powerful X-rays. This sort of pattern, called a power-law distribution, is very common in nature. For example, there are many cities with a relatively small population but only one or two with truly enormous populations. But at some point we would expect the power-law to come to an end because there has to be a limit somewhere to the energy involved in a flare. Unfortunately, this limit has never been seen in the data.

After being very quiet for the last two years, with few or no sunspots for months on end, at the end of October 2009 the Sun produced ‘active region 11029’. Appearing alone it gave Mike an excellent opportunity to study it in isolation. He discovered that it produced many weak flares, as expected, but no powerful flares. Careful analysis showed that it did indeed have the expected limit – something never before observed for an active region. The combination of an isolated active region and one that was small, and therefore incapable of producing very strong flares, had allowed Mike to make his fantastic discovery.

Given that several solar experts were present in the room I took the opportunity to ask for a consensus opinion – has the Sun woken up? Has the next cycle of activity begun? Yes! was the emphatic reply. This is good news for now we can expect to see plenty of large and active prominences, flares and sunspots during the Observatory’s regular solar-telescope viewing sessions.

As if to prove the point today (3 February 2010) the Sun produced a magnificent eruptive prominence. It stretched tens of thousands of kilometres above the Sun’s surface and several hundred thousand kilometres around the limb. Incredibly, we could see it change shape as we watched, something not usually visible. The image below shows the changes over approximately ten minutes! Yes, I think the Sun has finally woken up for solar cycle number 24.

Image by Geoff Wyatt and Andrew Jacob


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