Astronaut Records Unidentified Light Flashes
Posted Sep 9.03
Excerpted from Ed Lu's Journal: Entry #11: Dark Side of the Earth
Closer to home, whenever we pass south of Australia at nighttime we get to see the green and orange curtains of the aurora. Since most of our mission has been during the summertime in the northern hemisphere, we haven't gotten to see much of the northern lights over Alaska since it has been mostly in daylight.
Lately though, as the seasons are changing we are starting to get some nighttime views of the northern lights. About two months ago I saw something interesting and still unexplained, when watching the aurora. We were south of Australia, and the sun had just set. I was watching Mars rise up through the atmosphere as we flew eastwards. The aurora was off to the right, and was fairly bright that day.
A couple minutes after Mars had cleared the upper part of the atmosphere, I turned my attention to watching the aurora, when I saw a flash of light amidst the auroral curtains. It was a small point, but it was brighter than a typical star, maybe about the same as a 1st or 2nd magnitude star. It lasted maybe a second or so.
Then I saw another flash, and then another - all together maybe five or six flashes over a period of about a minute or two. I'd never heard of anyone describe such flashes coming from the aurora, and in researching it further, I still haven't! Perhaps we've discovered something new. But first we had to rule out some other explanations. When the station crosses over the day/night line, we are at an altitude where we are in sunlight for a few minutes while the ground below is still dark.
Small dust particles, which are continually shed by the Station, scatter the sunlight and are easily visible against the black background. You can see the same effect when looking at a sunbeam shining in through a window - you can see all the very tiny dust particles floating in the air. It turns out that some of the tiny particles (mostly paint flecks) that come off the Station are actually big enough so that they can look like a twinkling star as they float away and rotate. So when looking out the window at these times when we are in sunlight but the ground below is dark, you can often see little bright specks slowly drifting away from the Station.
We were able to rule this out by finding out the exact time I saw the flashes. Our navigation experts in Mission Control were able to work out to the second when Mars rose above the horizon from our point of view, and using that we were able to say that the sun had already set several minutes earlier, so it is unlikely that I was seeing scattered sunlight from dust particles.
Next, we wanted to rule out lightning (which is known to sometimes extend upwards - these are called sprites). I don't remember seeing any nearby lightning storms, but just to be sure we checked the weather maps and found that indeed the weather was clear. So that leaves us with a mystery. I've been watching the aurora carefully since then, but haven't seen this phenomenon again.
FS note: American astronaut Ed Lu is a NASA Flight Engineer onboard the International Space Station. As part of the Expedition 7 crew he is scheduled to return to earth in October.
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