Back in early December, Mars and Earth were at their closest to one another, a
point known as opposition. Mars has dimmed gradually since then, but it still
remains one of the brightest objects in the night sky, and certainly one of the
most vivid. While often known as the “red planet,” Mars is really more of a pale
orange, the result of abundant iron oxide (or “rust”) in its rocks, the same
substance that gives many of the rocks in southern Utah and western Colorado
their ruddy hue.
One way to tell the difference between a planet and a star is to study its light. The
light of nearby planets, like Mars and Venus, covers a larger area of the sky than
the stars. As a result, planets typically appear to shine with a steadier light, in
contrast to stars, whose light often appears to “shimmer” or “twinkle” due to
turbulence in our atmosphere. While this method isn’t foolproof, it works most of
the time!
Ultimately, it is Mars’ movement that betrays its planetary nature. On the scale of
human lifetimes, the stars remain in more or less fixed patterns, known as
constellations. Planets, however, “wander” across the sky, waltzing through
constellation after constellation as they orbit around the Sun. It is this behavior
that gives them their name: the ancient Greeks called these objects “aster
planetes,” or “wandering stars.”
This wandering is easy to see for yourself. Right now, Mars is just a little north of
the bright star Aldebaran, part of the constellation Taurus. Coincidentally,
Aldebaran also has a reddish hue. At the moment Mars is noticeably brighter than
Aldebaran, though this gap will close as we pull away from Mars in the coming
weeks. Note Mars’ position relative to Aldebaran and other nearby stars in
Taurus, then come back in a few weeks. Mars will have changed position, having
moved slightly eastward relative to the stars. All planets exhibit this motion,
though the more distant planets, like Jupiter and Saturn, do so more slowly, a
consequence of their greater distance from the Sun.
Western Slope Skies is produced by the Black Canyon Astronomical Society and
KVNF Community Radio. This feature was written and voiced by Zach Schierl.
