Sky and Telescope - July 2018 - 27
A LBEDO M A RK INGS: DA MIA N PE ACH; SK E TCHES: BOB K ING
One of the most dramatic events to witness is
a dust storm - as long as it doesn't expand to
become a planet-encircling event! This last
occurred in June 2007, when, within a few
weeks, dust had blanketed nearly every feature from view. Fortunately, such planetwide events are uncommon, with just 10
recorded over the past 130 years.
The more often you observe Mars, the
more familiar you'll be with any changes in
the appearance of albedo features that mark the
onset of a dust storm. Watch for a familiar feature
to disappear or a light area to appear. Visually,
dust storms appear as bright, yellow patches. A
#23A red ﬁlter will brighten and enhance the
view and serve to conﬁrm that you're seeing
dust and not water vapor clouds.
Dust storms are common during the
Martian southern summer, which begins
in mid-October. Good spots to keep an eye
on include the Chryse region and HellasNoachis from late August through November.
t NIGHT WATCH The author drew two sketches of Mars,
two hours apart, as viewed with a 10-inch telescope
at 256× on August 4, 2003 UT. The sketches show
the planet's rotation as well as several of its most
prominent features, including the dark "finger" of
Syrtis Major and the south polar cap. In the bottom
view, a dark rift shows in the cap. Such rifts appear
as the cap shrinks.
eye. Since the post referred to its apparent
diameter, it was correct. Multiply 25″ × 75 and
you get 31′, the full Moon's apparent diameter.
Then an unfortunate thing happened. As the
email made the rounds, the reference to "at a
modest 75-power magniﬁcation" was left out,
leading neophyte skywatchers to expect
a frighteningly large, Moon-sized Mars
casting a rusty specter over the landscape.
Like a mosquito you hear but forever fail
to swat, the description has popped up at
every subsequent opposition. Watch for it
to reappear on schedule this apparition, and
when friends ask what's up, patiently explain
and then direct them to the real thing right
Phobos and Deimos
that will inevitably spin out of social
Close oppositions provide a perfect opportunity to
media to your advantage to share Mars and the joys of lookobserve the Martian moons, Deimos and Phobos. Without
ing up with those new to the hobby. And it won't hurt one bit
the planet nearby, even a 3-inch telescope would be up to the
if you mention how important minimizing light pollution is
task: their 2018 opposition magnitudes are 11.5 and 10.5,
for a great dark-sky experience.
respectively. But Deimos strays just 1.2′ (arcminutes) and
Phobos only 21″ from the planet at best, so you'll need at
least a 10-inch instrument and careful planning. First and
¢ Contributing Editor BOB KING has been an avid observer
foremost, make your attempt around opposition when the
since childhood. He's a long-time member of the American
moons are brightest and their angular distance from Mars is
Association of Variable Star Observers (AAVSO) and author
at maximum (see page 52).
of multiple observing guides, including Wonders of the Night
I saw both moons during the 2003 perihelic opposition of
Sky You Must See Before You Die. Visit his blog at astrobob.
Mars in an 11-inch Schmidt-Cassegrain telescope by hiding
the brilliant planet behind an occulting strip made of aluminum foil taped across the ﬁeld stop of an ancient orthoscopic
eyepiece. With Mars safely hidden and a magniﬁcation of
233× applied, Deimos was an obvious pinpoint of light in
Though the internet is often a tool for rumormongerthe glare. Phobos, though brighter, orbits much closer to the
ing, it can also provide good information for planetary
planet and proved much more challenging.
observers. Here are a few sites to visit during this opposition of Mars.
Go for it and surprise yourself. Several planetarium-style
u Sky & Telescope Mars
u The 2018 Perihelic
software programs including the free Stellarium (stellarium.
Opposition of Mars
org) display the moons, allowing you to plan your observmarsproﬁler)
ing session when either is at maximum elongation from the
u Association of Lunar
Be a Planetary Ambassador
Finally, don't forget to get the public involved. Who could forget the internet rumor started in 2003 about Mars appearing
as big as the full Moon at opposition? I won't quote the full
e-mail that bounded from inbox to inbox, but surprisingly,
its content was mostly true, as it claimed Mars through a 75×
eyepiece would look as large as the full Moon to the naked
and Planetary Observers (ALPO) Mars Section
u The Red Planet (https://
How to Make An Occulting Bar (https://is.gd/
u Mars Observers Yahoo
s k y a n d t e l e s c o p e . c o m * J U LY 2 0 1 8