Ed Lu’s Journal: Entry #11: Dark Side of the Earth

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.