Physics Photo of the
October 28, 2011
Meteors or Satellites?
Photographing stars on October 16, 2011 to
measure their brightnesses, one of the images had a bright
streak at lower center. On careful inspection there is a
fainter streak near the center of the photo. I initially
thought I had "captured" two separate meteors within the 30
second frame. Airplanes are ruled out because they
usually leave a blinking trail. I was able to conclude
that these streaks both are caused by satellites because I had
taken a series of 30 second exposures in immediate
succession. Meteors would only show up on one frame because a meteor lasts
only for about 1-2 seconds. Satellites, on account of their
orbits, cross the sky much more slowly passing the field of
view in 2-3 30-second frames.
At right a sequence of highly-processed consecutive
frames are shown. The faint streak is visible in all
three frames indicating the object took about 180 seconds to
pass the field of view - definitely not a meteor. The
bright streak highly visible in the bottom of the middle image
looks like a meteor that was visible for about 2 seconds
during the 30 second exposure time for the middle image.
However, on close examination, the image immediately before
that of the bright streak shows a "ghost" of a streak of the
object that produced the bright streak as if the object moved
from upper right towards bottom center. This indicates
that the bright object was also moving slowly like the faint
object, but brightened during its pass through the middle
frame. This could be caused by reflected sunlight from a
solar panel or a polished antenna as the angles between the
Sun, spacecraft, and observer are just right.
There are a number of communications satellites, called
"Iridium" satellites that are well-documented and produce
bright flares at predicted times. From any location
anyone can log onto certain websites and find predictions for
flares produced by these satellites. My new goal for a
future PPOW is to photograph these documented flares. I
could not find a documented predicted flare for the evening of
Oct. 16. Some satellites are no longer maintained, and
the predictions for flares have ceased.
On the photos, the bright object passes through the
constellation Perseus just above the horizon. The camera
was tilted relative to the horizon.
Physics Photo of the Week
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