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RISING MOON I A fortnight of features
PACKED WITH DETAIL , the large crater
Posidonius is near the top of most lunar lovers’
lists. The lava-filled interior of this 60-mile-wide
ancient impact sports cracks, jumbled peaks
poking up from the floor, an off-center craterlet,
and bright segments of slumped walls.
Unlike most craters, which seemingly vanish
at Full Moon, Posidonius boasts a bright rim
with a cream pie face; one that’s full of detail on
the inside and lasts through March’s first week.
Changes in terrain heights from long shadows
that were obvious the previous week disappear
under a high Sun. Instead, the variety of
gray we see comes from the differences
in albedo, or reflectivity. The darker lava
on the flooded floor contrasts nicely
against the brighter specks left by small
impacts and the highlight of a long arc
of slumped terrace that faces upward.
When the Sun sets over this region late
on the evening of March 13, the shadows and
highlights will be reversed compared with the
image here, getting longer as the minutes pass.
This is a prime time to track how lunar features
become increasingly exaggerated, but a close
second is watching them march into lunar day
when the Moon is an evening crescent on the
29th. The raised rim with its companion eyeline-
like shadow is striking.Details abound in and around this 60-mile-
wide crater, which sits on the northeastern
edge of Mare Serenitatis. CONSOLIDATED LUNAR
AT L A S/UA/LPL; INSET: NASA/GSFC/ASUHyades star cluster. By March
29, the Moon, the Hyades, the
Pleiades, and Venus all lie in
a 17°-wide circle as Venus
crosses into Taurus. Venus
ends the month less than 3°
from the sparkling Pleiades
star cluster (M45) in Taurus
and will grow closer still in
the first few days of April.
If you target Venus with
your telescope during March,
you won’t be disappointed.
You’ll see the planet’s Earth-
facing hemisphere morph from
a plump 62 percent lit to just
47 percent lit over the course
of a month. Over the same
span of time, Venus’ disk goes
from 19" to 26" across. Though
a true half-lit Venus occurs
March 26, due to Schröter’s
effect, you can observe the
split-view up to six days earlier
for eastern elongations. Take a
look and see what you think.
Thanks to lighting effects
along the terminator of Venus
and the scattering of light in
our atmosphere, determining
the planet’s exact 50 percent
phase is a difficult challenge.
In the predawn sky March 1,
Mars, Jupiter, and Saturn
span 19° along the ecliptic. The
trio put on a stunning show all
month as Mars cruises past
both giant planets. From mid-
northern latitudes, you can
target the worlds above the
southeastern horizon between
5:30 a.m. and 6:15 a.m. local
Posidonius
BAPosidoniusNEEasily confused with Poseidon, the Greek god
of the sea, Posidonius is actually named after a
Greek astronomer and philosopher who lived
around 100 B.C. Look for Posidonius in the north-
east quadrant of the Moon. Posidonius B is a
noticeable 9-mile-wide fresh impact on the
northeast rim, while the slightly smaller crater A
has the sharp edges of youth. Age is relative,
since a fresh feature is 100 million years old.— Continued on page 42
MARS sits 42' south of Jupiter
the morning of March 20. Mars’
0.9-magnitude orange glow
contrasts nicely with Jupiter’s
magnitude –2.1 yellowish light.OBSERVING
HIGHLIGHT
METEOR WATCH I Glimpse the solar system's dim glow
MARCH IS THE PERFECT MONTH
to glimpse isolated meteors not
associated with any known showers.
And even if you don’t spot any random
streaks, March is still ideal for capturing
views of zodiacal light. This faint glow
is the result of fine debris — left by
eons of long-since-faded ancient
comets — littering the ecliptic plane.
Once twilight has passed, look for a
cone-shaped light above the western
horizon. In order to spot it, you’ll need
a dark and moonless sky. The feeble
glimmer is aligned with Earth’s orbital
plane, and passes through Pisces,
Aries, and Taurus. Use peripheral vision
to scan from left to right to spot the
darker skies on either side of the weak
glow. With a Full Moon on March 9, the
best times to view zodiacal light are
after the second week of the month
before moonrise.Spot a fleeting flash
Sporadic meteors can show up without
warning, like this one captured from Yosemite
National Park in August 2013. TONY ROWELL