Physics Photo of the Week
A meteor, an airplane, or a satellite?
conducting star photography on April 9, 2010 at about 9:00 pm, a bright
light was noticed in the east. Because the photos used a long
time exposure (15 seconds), any movement during the exposure results in
a streak of light. Is this streak a meteor, an airplane, a
satellite, or some UFO? If you look carefully in the top center
of the photo, a another faint streak (red) can also be seen.
Luckily a series of sequential images were made, each image consisting
of a 15 second time exposure. The resulting time lapse is animated
in the image below. Notice that the bright streak can be seen in
each of the frames of the animation, but moves between the
frames. The faint red streak at the top can be seen only in the
final four frames moving from right to left. If these streaks
were meteors, they would be visible in only one frame, because meteors
are visible for only about 1 second. These streaks move too
rapidly to be a distant satellite. They aircraft - the lower
aircraft has its headlights on for an approach to an airport - either
Asheville, NC or Greenville-Spartanburg, SC. The upper aircraft
leaves a dotted trail due to the blinking of its running lights.
Even though aircraft move much more slowly than satellites, they appear
to move much more quickly because they are much closer to us than
We can see two other effects in these series. Within the time
span of the animation, the sky becomes progressively darker in each
successive image. Twilight is gradually sinking into
darkness. Notice also that the stars appear to move slightly
between the images. The "motion" of the stars is due to Earth's
Photo of the
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 firstname.lastname@example.org.
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
the Week Archive.
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