Sky & Telescope - January 2025 - 49

hemisphere spring began on Mars
last November, when the clouds of
the North Polar Hood slowly began to
part and reveal the polar cap. As the
season progresses, the NPC's carbondioxide
ice sublimates and exposes the
permanent water-ice lying beneath.
A dark collar of basaltic sand dunes,
part of which comprises Mare Boreum
(see map), encircles the NPC and helps
define its boundaries. The dunes typically
become more prominent as spring
deepens and the cap shrinks.
Prominent dark albedo features in
the northern hemisphere include the
vast, low-lying plain of Mare Acidalium,
which looks like a truncated version
of Syrtis Major, the enormous, thumbshaped
shield volcano in the planet's
southern hemisphere. Niliacus Lacus
and Oxia Palus appear as dark, southward
extensions of Mare Acidalium. See
if you can also spot the dark hump of
Utopia - another northern-hemisphere
albedo feature, located at about the
same latitude as Mare Acidalium but
north of Syrtis Major. To Utopia's south
you'll see a large, pale expanse dubbed
Utopia Planitia. With a diameter of
about 3,300 km, it's the largest known
impact basin in the solar system. It's
also where NASA's Viking 2 lander
touched down in September 1976.
On nights of very steady seeing,
additional dark markings materialize
from the Martian glare. Some of
the easier ones include Sinus Sabaeus,
Sinus Meridiani, Mare Tyrrhenum,
Mare Cimmerium, Aurorae Sinus, and
Mare Erythraeum - all located in the
southern hemisphere. South of Syrtis
Major, look for Hellas, a large, circular
impact basin with a pale floor. When
it's covered in frost or overtopped by
clouds, it mimics the appearance of the
South Polar Cap.
If you manage to see these, try for
subtler features such as Solis Lacus,
Idaeus Fons, and the towering extinct
volcano Olympus Mons. Every opposition
I look for orographic clouds hugging
its slopes. I succeeded once!
Color eyepiece filters work wonders
on Mars. A light-red Wratten 23A for
smaller scopes and deep-red Wratten
25 for larger instruments will show
dark albedo markings more clearly. For
clouds and limb haze, a blue Wratten
80A or 38A improves the contrast. A
magenta filter (Wratten 30) enhances
both surface and atmospheric details,
while an orange Wratten 21 can help
identify and enhance the visibility of
dust storms. Although most major
storms occur during southern-hemisphere
summer, they can appear anytime,
so remain vigilant. As the NPC
continues to shrink during Martian
spring, powerful seasonal winds can
whip up a dust storm in a hurry.
A day on Mars lasts approximately
39 minutes longer than one on Earth,
so a feature on the Martian central
meridian will reappear there 39 minutes
later on the following night. If you
view Mars at the same time on successive
nights, the planet will seem to
slowly rotate backwards.
To find out which face of Mars you're
observing, use our online Mars Profiler
Tool at https://is.gd/marsprofiler.
Associate Editor Sean Walker captured this
Mars occultation sequence on December 8,
2022. " Mars drifted behind many craters for
about 12 minutes or so before finally lifting
away from the Moon's edge, " he wrote. The
Moon covers the Red Planet again this month
on the night of January 13-14.
The Moon
Occults Mars
MARS HAS MORE in store. On the
night of January 13-14, the full Moon
occults the planet for observers in the
contiguous United States, much of
southern and eastern Canada, Mexico,
and West Africa. Use your favorite
planetarium software or google " International
Occultation Timing Association
Mars occultation 2025 " for
disappearance and reappearance times
for your location.
From Chicago, Illinois, for example,
the Moon and Mars are less than 2°
apart as they rise together in evening
twilight. At 8:07 p.m. CST, the Moon
encroaches on the planet, taking about
29 seconds to completely cover it.
More than an hour later, at 9:16 p.m.,
Mars slowly returns to view on the
opposite limb.
During the December 2022 Mars
occultation, I tried to keep sight of
Mars right up to the lunar limb with
just my eyes. I failed miserably, losing
the planet in the full Moon's glare nine
minutes before it disappeared. However,
it was clearly visible in binoculars
right up to the moment of occultation.
Viewed with my telescope, what struck
me most was the compelling color
contrast between the Red Planet and
the gray Moon. I also vividly recall the
wonder I felt watching Mars seemingly
rise above the lunar horizon as the
Moon inexorably drifted away.
Both objects are bright and show up
well in photos taken with a telephoto
lens on a tripod. Smartphone users can
get excellent images when the device is
aimed at the eyepiece of even a modest
telescope. This method works best with
a dedicated mounting bracket.
Good luck and take care not to let
your fingers freeze!
sk yand tele scope .o r g * JANUARY 2025 49
https://www.is.gd/marsprofiler http://skyandtelescope.org
Sky & Telescope - January 2025

Table of Contents for the Digital Edition of Sky & Telescope - January 2025
