Saturday, December 4, 2010

update for Dec 5

At this point, we have been trying to launch the rocket for the last several days with no luck. It has been very windy here, still, which has made things difficult, and we have not had much aurora. This morning (it is 10 PM on Saturday as I write this, but 4:00 AM on Sunday).

Let's get back to some science and, in particular, the sun. Below, I put a picture of the sun taken from the Solar Dynamica Observatory (SDO) satellite. You can look at these any time yourself at this link. As of the time I am posting this picture, it is less than an hour old!!

You can see that a lot is going on here. For us, the important things are the bright spots, so-called "active regions", and the darker spot mostly on the left side, called a "coronal hole". I'll explain why this is what we care about in a minute, but first, I need to make an important point, which is that the sun actually rotates, sort of like the Earth. I say "sort of" because it turns out that at its equator, the sun goes through a complete rotation in about 27 days; nearer its poles, the rotation takes up to 35 days!! This "differential rotation" can only be possible because the sun really is a gas, not a solid.

OK, now go  here and watch some movies of the solar rotation. The point here is that, as the sun rotates, the coronal hole and active regions drift across from left to right. So, when we say that we are watching the sun, we are monitoring these things.

Next step: here is a bit of a curve ball, though. The solar wind that comes from the coronal hole and active region gets sprayed out as the sun rotates, just like water gets sprayed out of a lawn sprinkler. The effect that you get with the lawn sprinkler is a spiral shaped spray of water. Not surprisingly, the same thing happens with the sun - the solar wind is a huge spiral shaped "spray"!! This means that when we look at the sun and see something like a coronal hole, we have to keep the spiral shape in mind and realize that the solar wind from that hole will only hit us a few days later, when the images of the sun show the hole to be about 2/3 of the way across. I hope this is clear.

Ok, that's the scoop with the sun for now. Let's jump ahead to what the solar wind does to Earth's magnetic field. I already mentioned that the electrically charged particles flow along field lines to carry energy from the solar wind to our upper atmosphere. What maybe was not obvious is how dramatic this effect can be. You can get an idea of the effect by watching a "movie" of a computer simulation here. There are a bunch of movies there, grab some popcorn and poke around. These are from Prof. Jimmy Raeder at UNH.

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