[00:00.00]Professor: Okay moving on, let me ask an open question, have any of you ever seen an aurora? [00:10.05]Hmm, maybe you’ve heard it called by its other name the northern lights? Caroline.
[00:17.09]Female student: Yeah, when I was little, it's the light in the sky, right? I was in Alaska on vacation.
[00:23.50]Professor: OK good, it’s in a very high latitudes, places like Alaska which is near the north pole of earth or area near south pole where you'd be able to a see an aurora best, so what did you think?
[00:36.53]Female student: Oh, I'm, I don't remember that well. I think it was like just this big stripe of light in the sky, sort of, like a big greenish band type thing.
[00:48.77]Professor: A band huh? Sort of like this?
[00:51.70]Female student: Yeah, I think so.
[00:54.18]Professor: OK great, yeah, looks like a band or a curtain and the greenish color is quite common but you see other shapes and colors too, for example: arcs or a red color, and you'd be able to see them when the sky is clear and dark. [01:10.19]And, and like I said you need to be in higher latitudes, Mat?
[01:14.16]Male student: I have to say this is the first I have ever heard of something like this, is it caused by, like, light pollution, like too much light shining up from some human source or something?
[01:26.45]Professor: Like I said you need a dark and clear sky to experience this and light pollution... Well why aren’t we taken a close look at these auroras.
[01:36.22]Male student: Alright.
[01:37.11]Professor: Uh, let’s start with solar activity and its interactions with earth magnetic field. [01:43.07]See the sun as you know, on the sun you have constant activity, like explosions and plasma, the sun’s matter just sort of seething all the time. [01:53.52]The explosions from the sun they blow tons of super hot, electrically charged particles out into to space. [02:00.78]These particles break off from the sun and blow away in all directions. This movement of charged particles is called “solar wind”.
[02:09.27]Male student: I see, so you're saying the solar winds is the cause, but then uh, if the solar wind is blowing from the sun every which way, how come you could only see an aurora in polar regions or near polar regions?
[02:23.91]Professor: Think of earth as a one big giant magnet. [02:28.17]So, earth is surrounded by a magnetic field, and we know that every magnet has a north and a south pole and things get oriented toward those poles. Earth is no exception, right?
[02:39.80]Male student: Right.
[02:40.52]Professor: Okay, keep in mind that solar wind is electrically charged, which means that it interacts with the magnetic field as electromagnetic theory tells us. [02:51.56]Okay, how does it interact? [02:54.46]Earth, magnetic field deflects most the solar wind, makes it flow around the earth without getting very closed and that’s actually quite important because these high energy particles could be dangerous for living organism like us if they ever reached the earth’s surface. [03:12.39]Some are the charged particles derived from solar wind however, do get closer. [03:19.27]But those are channeled by the magnetic field toward earth poles or polar regions, that's where they hit the upper atmosphere and create, light, the aurora.
[03:30.90]Female student: Hmm, how do the particles create light?
[03:35.95]Professor: Good, let’s talk about the atmosphere. It’s mostly made up of nitrogen and oxygen, right? [03:41.18]It’s thickest closer to the earth surface, gets thinner as you go up, that's why it’s easier to breathe at lower altitudes. [03:49.19]And we get most of our weather and the lower atmosphere in the first ten miles or so of it. [03:54.72]As for the aurora, its lowest edge is about sixty miles above earth surface and can go up hundreds of miles from there, Okay? [04:05.16]So, you have those charged solar wind particles hitting the upper atmosphere near the poles, right? [04:12.25]These are high energy electrons, and what happens is, these electrons collide way up in the atmosphere with the molecules of the gases that are there, Mat?
[04:24.16]Male student: You mean oxygen and nitrogen.
[04:27.10]Professor: Yes, the gases that make up the atmosphere. [04:29.51]So, some of the energy from the charged electrons gets transferred to oxygen and nitrogen molecules, which causes the molecules to get into and excited state, which is a technical term for molecules with extra energy. [04:45.05]But these molecules hold on to that energy, just briefly and then let it go and the energy they let go, comes out this light. [04:54.93]So, when this happens to a lot of molecules at once, they can produce enough light that is visible to people.
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