Explanation:
M33 is
a big, beautiful spiral galaxy a mere 3 million light-years
away, understandably a popular target for enthusiastic
astro-imagers.
Just as understandably, interfering
satellitetrails and
airplane streaks that are
becoming more common in
planet Earth's busy night sky are
processed out of their
finished images.
But Robert Stephan left these streaks in his
final
picture of M33, realizing that he had also recorded
something relatively rare.
His otherwise cosmic skyscape shows the tail of
an aircraft passing overhead through his telescope's field of view.
A navigationalstrobe light
on the plane
flashed across the tail at exactly the right moment.
The brief illumination produced the incongruous,
though remarkably sharp image.
