How the Sun got its groove back.Posted: July 8, 2009
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Having just had a “heat wave” here in Scotland we were all reminded that a giant ball of hot gas does indeed grace the sky on a regular basis however two consecutive sunny days in Edinburgh was not the only recent interesting event involving the sun. The Sun, like a middle aged man undergoing a midlife crisis, has donned its leopard print attire once again and after a long absence it has a sunspot again.
The sun is a curios object, despite being the closest astrophysical object to us (apart from the moon and a few other rocks) we still dont know exactly how it ticks . Part of the difficulty is that we can only see a short distance inside the Sun, beyond this the plasma the Sun is made of scatters the light so much it becomes opaque. The most prominent feature on the surface of the sun is normally collections of sun spots: darker patches against the bright background of the solar body. These spots are regions of intense magnetic fields on the surface of the sun and just like a magnet and iron filings the hot plasma traces out the complex magnetic field which can be clearly seen in the close up image below. The magnetic fields in these regions interfere with convection: the proses by which heat makes its way from the depths of the sun to its surface, as a result the sunspots are a cool refreshing 3700 degrees Celsius compared to the surrounding material which is at about 5600 degrees. This comparative frigidity makes the spots dark in appearance
One of the curious aspects of the sun is that it undergoes roughly an 11 year cycle in which the number of sunspots rises and falls. This period is very regular and has been active ever since sunspots have been recorded. Recently we have been in a quite phase of the cycle which was supposed to end late 2007 early 2008 but apart from one small sunspot December last year the sun has remained largely quiet. Its not the first time this has happened as well, records show that around the 1650’s there was a similar (and indeed longer) drought which corresponded to the coldest period of a time know as the “little ice age”. Now before we all get in to a panic and decide on the ridiculous plan of sending some astronauts to bomb the sun back in to activity (they will only go mad and kill each other anyway) I should tell you the good news. A new robust set of sunspots seems to have appears on the sun in the last few days which can be seen in the movie above. Phew, it will be a little longer before we can be sure that a new cycle has stared in earnest but its a good sign. So why was there such a prolonged period of quiet.
Well as I said we dont understand the sun fully because we cant “see” inside it, well that might have been what Terry Pratchet likes to call “a lie to children” (not that I think you are children… unless you are I suppose in which case good for you 🙂 ). Light is scattered too much by the sun to be of any use but sound waves are free to pass through the sun easily. We see these waves at the surface of the sun as moments of the material there which we can use to infer whats happening deeper in the sun. In what is perhaps the coolest sounding name for a field of Scientists, asteroseismologists study these vibrations on the surface of the sun like regular seismologists study the vibration of the surface of the Earth to figure out what is going on in our own planets core. A group of these scientists at a conference in Colorado recently announced that they had observed and tracked jet streams about 7000km bellow the surface of the sun. These streams appear to form once every 11 years at the suns poles and migrate to the equator, it also appears that when they reach a latitude of 22 degrees they trigger the next cycle of sunspots. The most recent of these jet streams has been moving slower than the pervious, sluggishly working its way down and has only just recently arrived at the magic latitude. This could be an explanation of why we are just seeing sunspots appear now but there is still a lot to learn, how do the jet streams induce sunspots, why was this last one sluggish, how are the jet streams created themselves and perhaps more importantly who came up with the plot to Sunshine and did they know anything about physics, the answers to all of these (apart from the last one ) will have to remain a mystery just now but watch this space for breaking updates as science continues its slow but inevitable march.