On June 4, 2010 Regulus, alpha star of the constellation Leo,
and wandering planet Mars were at about the same apparent brightness,
separated on the sky by 1.5 degrees.
An ingenious and creative 10 second exposure from
a swinging camera
recorded these gyrating trails of the celestial pairing.
Can you tell which trail belongs to the star and
which to the planet?
Hint: atmospheric turbulence causes the image of the
star to scintillate or
vary in brightness and color more readily than the planet.
The scintillation is more pronounced
because the star is effectively a point source of light seen
as a narrow bundle of light rays.
refraction due to
turbulence along the
line of sight affects
different colors of light by
different amounts and generally produces a
effect for stars.
But Mars is much closer than the distant stars and an extended
source of light.
Though tiny, its disk is seen as a bundle of
light rays that is substantially broader compared to
a star's and so, on average,
less affected by small scale
The result is the varied,
rainbow like trail for Regulus (left)
and the steadier, consistently reddish trail for Mars.
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