Physics Photo of the
November 4, 2011
This is the reflection of
sunlight off a polished antenna section of a communications
satellite called an "Iridium Satellite". The position
and orientation of the satellite is very well-known allowing
computer programs to accurately predict when and where the
mirror-like surfaces will briefly reflect the sunlight to a
spot on the Earth. Once such prediction program is
available at the website that is developed and maintained by
Chris Peat: HeavensAbove.com.
At Warren Wilson College several flares were predicted each
week in late October and early November, 2011.
We often see the sunlight reflected off approaching car
windshields if the Sun is in the proper position so that the
windshield briefly emits a flash toward on-coming
traffic. Other common situations occur when the setting
Sun is reflected in windows of a distant house. With the
stationary window reflection, the flash lasts a couple of
minutes. The satellite flare is a similar phenomenon.
The image above consists of two 15-second time exposures at
about 6:15 am on October 25, 2011. The gap in middle of
the streak is caused by the camera shutter switching between
exposures. The flash from an Iridium satellite lasts
about 10 seconds. Physics assistant Mayuri
Patel processed the above image by stacking
about 10 images. The bright star just to the right of
the satellite streak is Polaris - the North Star.
Occasionally satellite streaks can be mistaken for meteors -
week's Physics Photo of the Week
At right is another flash event obseved on October 30 from the back yard of a WWC colleague Dean Kahl who lives in
Asheville, NC, several kilometers from WWC. East
Asheville area was the center of the maximum brightness for
the October 30 flash at about 7:24 pm. At the Asheville
location the flash was bright enough that we could photograph
the flare with only 1/2 second shutter times. About 10
images are played back in real time in the animation.
The flash lasts for several seconds and is about 100 times
brighter than the brightest stars visible.
The Iridium satellites serve "satellite phones" - cell-type
telephones that can be used in any location in the world using
the network of about 60 Iridium satellites instead of
stationary cell towers. The satellites orbit the Earth
about 500 km above the ground level.
Physics Photo of the Week
is published weekly during the academic year on Fridays by
the Warren Wilson College Physics
Department. These photos feature interesting
phenomena in the world around us. Students, faculty,
and others are invited to submit digital (or film)
photographs for publication and explanation.
Atmospheric phenomena are especially welcome. Please
send any photos to email@example.com.
All photos and discussions are copyright by
Donald Collins or by the person credited for the photo
and/or discussion. These photos and discussions may
be used for private individual use or educational
use. Any commercial use without written permission
of the photoprovider is forbidden.
to see the Physics Photo of the Week Archive.
Observers are invited to submit
digital photos to: