This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

NASA Science News for March 24, 2003

Space Station Astrophotography

Astronauts onboard the International Space Station are capturing some
amazing photos of the night sky. 

March 24, 2003: It's a weird place for an astronomer. Meteors fly
underfoot. Auroras appear just inches in front of your nose. City
lights twinkle, but stars don't. 

Astronaut Don Pettit loves every minute of it.

"There's always something good to see out the window of the space
station," says Pettit, who happens to be an amateur astronomer as
well as the science officer of the International Space Station (ISS). 
                                                                     
"Lately we've been having some extraordinary auroras," he reports.
"They meander like big green amoebas crawling across the sky.
Sometimes there is a faint touch of red layered above the green.
These lights are constantly changing. They swirl. Bright spots come
and go. Green blobs transform into upward-directed rays topped by red
feathery structures." 

Long before he went to live onboard the space station, Pettit was an
avid aurora watcher. "I've taken photos of the Northern Lights from
Alaska and Canada," he says. Some of those displays were magnificent,
but "the view from station is even better." 

Auroras are caused by electrons and protons from space raining down
on Earth's atmosphere. The solar wind, through a set of complex and
fascinating interactions with the Earth's magnetic field, is the
ultimate source of energy that drives these particles toward our
planet. When they hit the top of the atmosphere, they excite atoms
and molecules and make the air glow. Reds and greens come from atomic
oxygen, blues from nitrogen. 

These colorful lights range in altitude from 80 km to 500 km above
Earth's surface. The ISS orbits our planet about 400 km high, so the
space station can actually fly through auroras. There's no danger to
astronauts, though. The aurora-causing electrons and protons are
thousands of times less powerful than potentially hazardous cosmic
rays. 

"[Last January] we flew through an auroral curtain over Canada,"
recalls Pettit. The station was surrounded by a dimly glowing red
fog. Just below were green rivers of light. "It was like I had been
shrunk down to some miniature dimension and inserted into a tube of a
neon sign. And it was just on the other side of the window pane. I
wanted to reach out and touch, but of course I couldn't." 

"Afterwards I had to clean my nose print off the window."

Auroras aren't all: "I've seen an occasional meteor while looking
down through the Destiny Lab window," he says. Meteors disintegrate
in Earth's atmosphere below the space station, so you have to look
down to see them! "You can also see space junk orbiting nearby.
Sometimes it flickers due to an irregularity catching light as it
rotates. And there are satellites, too. A flash of sunlight glinting
off an Iridium satellite near the Southern Cross really brought a
smile to my face." 

Pettit recently took some lovely pictures of star fields in the
southern hemisphere: the Large Magellanic Cloud (a nearby galaxy that
orbits our own Milky Way galaxy), the Coal Sack Nebula (an inky-black
interstellar cloud), and the Southern Cross. 

"These pictures show how wonderfully stable the space station is,"
says Pettit. "When the camera is mounted to the window, the ISS
itself serves as a tripod. Any movement would cause streaks in the
star images." But the station's Control Moment Gyros maintain
attitude with rock-solid precision. "I don't believe that the ISS was
designed for astronomy," adds Pettit, "but it functions very well as
a platform for astrophotography." 

One of the curious things about sky watching from orbit is the
appearance of stars. "They don't twinkle," says Pettit. Twinkling is
caused by irregularities in Earth's atmosphere that refract starlight
to and fro. But in orbit there is no atmosphere. Stars are remarkably
steady and piercing. 

City lights, on the other hand, do twinkle. "From the space station
we can see city lights when it's nighttime on the planet below,"
explains Pettit. "Shining upwards through the atmosphere, they
twinkle like stars. They're beautiful." 

When Pettit tried to take pictures of city lights he quickly realized
it wasn't as easy as photographing the stars. The station, traveling
17,500 mph, races around Earth in only 90 minutes. Lights on Earth's
surface move through the window too quickly for long exposures.
Stars, on the other hand, appear nearly motionless because they're so
far away. It's like driving down a highway in a fast-moving car:
Distant mountains and trees don't appear to move much, but the fringe
of the road is a blur. 

"I needed something to help me track the city lights, to cancel the
orbital motion of the station." 

Pettit is well-known to his friends as an ingenious gadget builder,
and it didn't take him long to devise a solution to the tracking
problem. 

"I assembled a 'barn door tracker'," says Pettit. "It's based on the
fine gimbal movements in the IMAX camera mount for the Destiny Lab
window. I figured out a way to mount a threaded screw and nut
(scavenged from a Progress rocket) and drive it with a Makita drill
driver." The drill turns the screw, which moves the camera and its
spotting scope. "All of these modifications clamp on to the IMAX
mount and do not change its original function in any way," notes
Pettit. 

"I manually compensate for the station's motion by looking through
the spotting scope and running the drill at the same time. It takes a
bit of practice, but you do learn to track." 

Pettit has since photographed cities and towns around the world.
"With tracking we can see individual city blocks--no blurring." Some
towns are well-organized like checkerboards. Others are more ...
organic. London, for example, resembles a glittering luminous spider
web splayed across the landscape. "Really nice," says Pettit. 

For sheer beauty, though, "my favorite is still auroras," he says. "I
can't get enough of them." 

Pettit is scheduled to remain onboard the ISS until May. Between now
and then, in his spare time, he plans to continue taking pictures and
sending them to Earth. There'll be more auroras, more meteors and
star clouds and city lights. 

And probably lots more nose prints on the window....

Credits & Contacts
Author: Dr. Tony Phillips
Responsible NASA official: Ron Koczor 
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Steve Roy

 - END OF FILE -
 ==========

@Message posted automagically by IMTHINGS POST 1.30
---