Sky and Telescope - July 2018 - 4

SPECTRUM

by Peter Tyson

A Meteorologist on Mars

The Essential Guide to Astronomy
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FOR THE BACKYARD ASTRONOMER, the Red Planet offers a certain

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DA MIA N PE ACH

rare opportunity, one that is particularly pronounced during ﬁne
apparitions like this year's, the best since 2003. It's something no
other planet can provide, and it's available to anyone blessed with
a modest-aperture telescope, good seeing conditions, and, as Bob
King puts it in his article on page 22, "the patience of marble."
That singular fortuity is simply this: If you train your scope on Mars, you
can actually see seasonal and even localized weather changes occur. I ﬁnd
that astounding. From the comfort of your favorite viewing location, you can
observe dynamic environmental phenomena on the surface of another planet!
(The only other planet whose surface we can view visually is Mercury, but its
tenuous atmosphere offers nothing, well, mercurial for the amateur observer.)
As this year's Martian southern-hemisphere spring progresses, you can
monitor winter mists dissipating to reveal the pearly white south polar cap.
Train your eye over days or weeks on that cap, which is currently tipped towards
us, and you can witness it gradually retreating as its ice sublimates. Gazing at
the planet's mid-section, you might catch sight of faint equatorial cloud bands, while at its edges, you can look for "limb
arcs," a bluish brightening caused by light scattered in dust
and dry-ice particles high in the atmosphere.
Try spotting the snow-white clouds, comprised of waterice crystals, that form in late spring and early summer above
Olympus Mons and the other Tharsis shield volcanoes.
Mars as it appeared
Watch, too, for bright "morning clouds" of ground-hugging
on March 31, 2018
frost or fog (on Mars's celestial eastern or following edge) as
well as their "evening" counterparts (on the western or preceding limb).
Finally, keep an eye peeled for what has been called in these pages "one of
the most spectacular planet-altering events in the solar system" - a major
Martian dust storm. These yellowish-tinted disturbances are especially noticeable when they blot out parts of dark albedo regions. Just pray the storm doesn't
grow to enshroud the entire planet, as one did in 2001 (see photo page 20).
While you're enjoying this standout apparition, you might ﬁnd yourself
contemplating other mysteries of the Red Planet. We address several of them in
this special issue: How did Mars lose its once-thick atmosphere (page 14)? What
tips can advanced observers offer for sighting the moons Phobos and Deimos
(page 52)? And why did a few astronomers in the early 20th century persist in
maintaining that Mars bears canals built by intelligent beings (page 28)?
We encourage you to make the most of this close
approach. You shall not look upon its like again for
another 17 years.

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Sky and Telescope - July 2018

Table of Contents for the Digital Edition of Sky and Telescope - July 2018