Space Station Science Picture of the Day 28 Mar 2003

 March 28, 2003



Iridium Flare

Credit: Don Pettit, ISS Expedition
6 Science Officer, NASA

with assistance from amateur astronomers
Rob Matson and Robert Reeves

Explanation: Two spacecraft circle Earth in different
orbits, each traveling faster than 17,000 mph. Sunlight bounces
off one and hits the other … but only for a split second. What
are the odds? International Space Station (ISS) Science Officer
Don
Pettit saw it happen–and photographed it (above)–on March
21, 2003. He was staring out one of the windows onboard the ISS
when an Iridium communications
satellite passed overhead. Sunlight hit one of the Iridium’s
mirror-like
antenna panels and bounced down to the
ISS; the fast-moving Iridium satellite seemed to flare like
a supernova! Sky watchers on Earth, using web sites such as Heavens Above to tell
them when to look, see these Iridium
flares often. The flares are trickier to predict for sky
watchers on the ISS, however, because the space station and the
passing satellite are both moving. Furthermore, the reflected
beam of sunlight is narrow–only ten or so kilometers wide. The
chances of the ISS passing through it are slim. Pettit knew when
to look thanks to the work of amateur satellite hound Rob Matson,
who wrote a computer program to calculate when Iridium flares
would beam through the windows of the space station. Using Matson’s
predictions, Pettit now sees as many as four Iridium flares each
day.