Monday, December 6, 2010

Update for Mon, Dec 6, 2010

Things are starting to get interesting. Most importantly, the solar wind is improving (the energy it is delivering to Earth is increasing) which is what we need to get the aurora we are looking for. We have been seeing aurora in some of the special auroral cameras we are running quite clearly. We could see that there were several auroral arcs overhead, sort of jumping around but fairly bright. This was encouraging, but we really need to have some fairly steady conditions. Why are we so fussy? Well, it comes from the countdown. We can sit at T-15 minutes indefinitely, meaning that we can watch what is going on, discussing whether the conditions look promising, etc. and just let the rocket (and crew) sit idle. When things start to really look interesting, we ask to "pick up the count", in which case the team at the launch range begins a certain countdown sequence. This is basically a checklist of items that need to be a certain way before we can launch. I'll talk about this more later, but it includes things like confirming there are no fishing boats under the trajectory and so on.

Usually, the count will be brought down to the T-2 minute mark and held. At this point, we are generally quite fidgety, watches every instrument we can find, anticipating the launch. We can hold at T-2 minutes for about 30 minutes, after which time we have to either decide to launch or go back to T-15 minutes. If we decide to launch, the final checks in the countdown are carried out and followed by the classic 10-9-8-7-6-5-4-3-2-1-launch. So, that's why we need steady conditions in the ionosphere overhead (that is, aurora!!).

About aurora...

Now is a good time to say some things about aurora, sometimes called Northern Lights. First, there is no question that aurora is one of the most spectacular things you can ever see. You do see it in New Hampshire at times, when a huge magnetic storm hits, but it is generally nothing like what you see as you get nearer the magnetic poles of Earth (yes, there are "southern lights", too). The things you notice right away is that there are many shapes and colors, that things are different from day to day or even from minute to minute. Naturally they're amazing to watch but, scientifically, aurora is very important because it is part of the last step in the process of transferring energy from the solar wind to our upper atmosphere.

I should say that we already know what causes aurora, at some level. This is a bit tricky for me to explain, since I am not sure of everyone's background, but here goes.... You have no doubt heard the term "atom", which maybe you know is the building block for the stuff we are familiar with from day to day. Everything we see around us (and maybe don't see) is built up from atoms; sometimes, an atom might be attached to one or more other atoms and then we call the building blocks molecules. For example, water molecules are made up of two hydrogen atoms and one oxygen atom, which is why it is sometimes written as H2O. This gets complicated real fast, but the part that we need to deal with is not so bad. For one thing, we almost always deal with just atoms by themselves.

Well, it turns out that atoms can get excited and, when they do, they respond by giving off light. That is, if you can manage to bump an atom somehow, you can expect it to give off a brief burst of light. This, in fact, is probably happening right next to -- look up at the ceiling. Is there a fluorescent light? If so, then you have "atomic collisions" and "photon emissions" taking place right where you are. By the way, the next time your parents ask you what you learned in school today, try telling them that you studied "atomic collisions" and looked at the "photon spectra" that resulted from it. You'll probably get a very silent reaction and then they'll stop asking that question.

OK, back to aurora. From experiments that can be done in a lab, we know lots about what colors of light we can get from different atoms. We also know that the specific color that you get depends on how hard you bump an atom (how much energy gets transferred to the atoms or molecules). From some very basic measurements made in the 1960s, we know that aurora is caused by electrons or protons (originally in the solar wind) drifting along magnetic field lines. So, if you can put this all together, here is what we can learn just by looking at the colors and brightness of aurora, for example:

1. The color alone can tell you what atom is being excited (e.g., the most common color is green, which comes from oxygen atoms). There's more - from experiments on the ground, we know that oxygen atoms emit lots of different colors, depending on what energy the electrons are that collide with them. So when we see green aurora, we know that we are seeing light emitted from oxygen that is being struck by electrons with certain energies.

2. The brightness tells you how many electrons are coming down the magnetic field line (the brighter the aurora, the more electrons we have).

Well, this makes watching aurora a handy way of understanding what is going on in the space above us. There are many different colors and shapes and from simple observations from the ground, for example, we can get an idea of how much energy gets transferred to our atmosphere when a coronal hole is present on the sun (this is cool stuff)!!!

Here is a photo from a rocket campaign that we had a few years ago, in Alaska. You can even see the rockets pointing up to the sky in the bottom of the picture

Today's points of interest.....

Here is something you don't see in New Hampshire, a polar bear crossing sign!!

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