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Re: Ed Lu's Latest Letter



Corrected URL is 
http://spaceflight.nasa.gov/station/crew/exp7/luletters/lu_letterlatest.html


73, Scott

----- Original Message ----- 
From: "Arthur Z Rowe" <n1orc@surfgate.net>
To: <sarex@AMSAT.Org>
Sent: Saturday, September 13, 2003 2:31 PM
Subject: [sarex] Ed Lu's Latest Letter


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> Expedition 7: Home | EVA | Timelines | Experiments
>
> Earth From Space Images
>
> Dark Side of the Earth(For pictures see:)
>
> http://www.station.nasa.gov/station/crew/exp7/luletters/lu_letterlatest.
> html
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>
> Some of the most incredible sights you can see from up here are on the
> dark side of the Earth, when the Sun doesn't dominate the sky. I like to
> go down into the docking compartment and turn out all the lights and
> watch the nighttime sky through the two portholes there. Just like at
> home, if you are indoors looking out through the window when all the
> lights are on inside, it is very hard to see the stars. Your eyes are
> adjusted to the bright interior, and besides all you can usually see is
> glare off the window. After turning off the lights, it takes a few
> minutes for your eyes to adapt to the dark, and slowly the stars get
> more and more distinct. These past couple of weeks the moon has been
> close to a new moon, so without the light from the moon, the stars seem
> even brighter.
>
> The view is something close to what you might see on a very dark
> mountaintop on a very clear night. Only better. Our solar system is
> located midway out from the center of the big disk of stars that is our
> galaxy. When you look in the directions along the disk you see more
> stars than if you look perpendicular to the disk. This is the Milky Way
> - the line of stars, gas, and dust that cross the sky, and it is
> incredibly distinct when viewed from here. We have a pair of image
> stabilized binoculars (that work by suspending the prism in some sort of
> fluid so it smoothes out the jitter), and through those I like to look
> at the various nebula and star clusters you can see when looking towards
> the center of our galaxy along the Milky Way. In truth, the view of all
> these objects is better with a real telescope on the ground than with my
> handheld binoculars, but there is something really cool about floating
> in a spaceship looking at all the stars!
>
> It is fun to watch stars as they rise or set through the atmosphere as
> we circle the Earth. They start to twinkle as the light rays bend while
> passing through the uneven density of the atmosphere. Then, as they get
> closer to the actual horizon, they start to look orange and then red
> before blinking out. Sometimes they even turn green briefly. This is
> just the same effect that makes sunsets look orange and red (if you
> wonder why that is, it turns out that dust in the atmosphere scatters
> blue light better, so when the blue color is taken out of something that
> is white, it appears reddish). In fact, it is really just a star set -
> the only difference with a regular sunset is that in this case the star
> is much further away! Actually, astronomers sometimes use this technique
> to study the atmospheres of other planets as they cross in front of
> stars.
>
> The bright red dot of the planet Mars has been a great sight recently,
> with Earth and Mars being very close now (relatively speaking). Here in
> low Earth orbit, we aren't significantly closer than you are on the
> ground to Mars, but without the atmosphere to look through it makes it
> clearer and brighter. It is bright enough that even when we are on the
> lit side of the Earth, and with all the lights on inside, it is clearly
> visible against the black background of space. With our binoculars or
> the high power lenses on the cameras you can see the disk of Mars, but
> we don't have anything onboard with enough magnification to really see
> the polar ice caps.
>
> 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.
>
> Well, since I only have a month and a half left before we come home, I
> better appreciate the view of the sky here while I still can!
>
>
> This is a photo of the aurora. You can see parts of the Space Station
> structure on the left.
>
>
> This is the crescent moon just over the horizon - taken with a telephoto
> lens. On this day there are rare high altitude clouds, known as
> noctilucent clouds. These are the silver looking clouds you can see
> above the orange color where most clouds are usually located. The dark
> bands in the orange section are the tops of thunderstorms, which extend
> up to about nine miles high.
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