Sunday, December 4, 2011

Predicting Aurora: Optics

So what better way of knowing if there is aurora than by looking at the optics! There are plenty of places to find data online, the one I check is run by some colleagues in Alaska, which can be found here. The site has some archived data, but is best for looking at real-time data (note that there won't be anything on the real-time pages if you look at them during daylight hours). Spend some time clicking around those different pages, at night, so you can see the different options. There are several different stations which are at different latitudes. If the aurora starts to move to lower latitudes there is a better chance that things will get very active.

Two of the main things you will see on this page are keograms (the rectangular ones) and all-sky images (the round ones). Let's talk about the all-sky images first, or ASI, as I'll probably continue to call them.

The ASI are probably easiest to understand, because they are pretty comparable to regular cameras. You can think of it as a regular camera that is viewing the entire sky. If you want a little more detail, imagine that you are lying on your back with your feet pointed to the North, and you are looking at the entire sky. The view of the entire sky that you see is the same projection that an ASI gives (so North is generally at the bottom of the frame, I apologize on behalf of the entire community). Some of the all-skies show white light (as in, what we would see with our eye, converted to black and white), and some show particular wavelengths (for example, 630.0 nm, which corresponds to the red aurora at higher altitudes).

The keograms are useful for knowing what the aurora has been doing over the past however many hours are plotted. One way of making a keogram is to take a slice of the all-sky image from the north to the south. Then you put a bunch of these slices together over time to show how the aurora has changed with time. Another option for the keogram (which is possibly more typical) is to use a Meridian Scanning Photometer, or MSP. An MSP is an optical device that measure photons (the light we see as aurora), but it generally doesn't use a lens like the all-sky does, so we don't actually call it a camera (hence "optical device"). The MSP, as the name implies, scans the meridian, so once again we are getting a slice of the sky from north to south, which is then plotted in sequence with time. I hope that makes sense to anyone who is not already familiar with a keogram.

For now this is all I have to write about predicting aurora, unless anyone has specific questions for me.

:) Thanks for playing.

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