Astronomy - USA (2021-12)

Dec. 14, 4 A.M.

Looking west

CANIS

MINOR

GEMINI

CANIS

MAJOR

AURIGA

Radiant

Pollux Castor

Procyon

Capella

Aldebaran

ORION

PERSEUS

TAURUS

Sirius

Pleiades

Betelgeuse

10°

WWW.ASTRONOMY.COM 33

RISING MOON I Nested craters

IT’S EASY TO FIND twin craters side by side

or small circles inside much bigger ones —

they’re everywhere — but a Goldilocks bowl

that’s just right, nestled inside its parent crater?

Boussingault in the far southeastern area of the

Moon is the best fit. It is visible from the 7th

through the 21st, as the Moon morphs from a fat

crescent to a couple of nights past Full.

At first glance, you might think that this is a

terraced feature, where the sides have slumped

inward after the impact excavated a large hole.

But after a few seconds, you will notice it defi-

nitely has a different appearance: Terraces

don’t have raised rims like the inner

Boussingault A. Thanks to its far south-

ern latitude, shadows hang around for

many days, keeping the double nature

distinct from the hundreds of other fea-

tures in these crowded and rough lunar

highlands. There is no central peak here —

the original one was wiped out by the second

impact, then lava pooled up from below to sub-

merge it all.

Boussingault K, a younger, sharp-edged

small crater, adorns the northern rim, clinching

the positive identification of your target. An

even smaller crater chips the southern flank. As

much as the turbulence in our atmosphere per-

mits, crank up the magnification and settle in for

a while. Thanks to the shadows and our slanted

background just short of the

Capricornus border and sinks

back into twilight. Track Venus

with a telescope to view its

changing form. On Dec. 1, it

shows a 28-percent-lit crescent

spanning 39". The disk grows to

61" by Dec. 31, but shrinks to a

mere 2 percent lit. This fast

transformation occurs when

Venus approaches inferior

conjunction, which occurs early

in 2022.

As Venus gets lower late in

December, Mercury appears out

of the Sun’s glare. Try spotting

the innermost planet Dec. 26,

when it stands less than 6°

below Venus. They appear

closest on Dec. 28 — 4° apart

— with Mercury shining at

magnitude –0.8. By New Year’s

Eve, Mercury stands 1° higher

than Venus. Check them out

45 minutes after local sunset.

Saturn joins Venus in the

evening sky, shining a much

fainter magnitude 0.6. They’re

18° apart on Dec. 1, and are

closest (14° apart) on Dec. 16.

Saturn remains in Capricornus

all month.

Grab your last telescopic

view of Saturn and its rings for

the year. The ringed planet is

best during the first half of the

month, when it remains

above about 20° altitude for

up to an hour after twilight

ends. In late December,

Saturn is too low for good

views in a dark sky.

Boussingault

view, the 3D appearance might give you a sense

of sitting in low lunar orbit.

Compared to our view this month, the pic-

ture above shows us a bit beyond the limb. The

slight nodding up and down of the Moon’s face

results from its orbit taking the Moon slightly

above and below the imaginary level field of

Earth’s orbit around the Sun (the ecliptic). This

particular image was taken with the Moon above

the ecliptic, revealing more of its underside.

— Continued on page 38

METEOR WATCH I One out of two

TWO MAJOR METEOR SHOWERS

occur in December each year: the

Geminids (Dec. 4–17, peaking on the

14th), and the Ursids (Dec. 17–26,

peaking on the 22nd).

A waxing gibbous Moon lies in

Pisces for the Geminids’ peak, result-

ing in moonlight interfering until our

satellite sets around 3 A.M. local time,

offering a couple of hours of dark

skies. The Geminids are one of the

most favorable shower of the year,

with close to 150 meteors per hour

when Gemini is near the zenith.

Although the Moon will affect this

rate heavily, patient skywatchers can

wait for the occasional bright event,

which are usually spectacular.

The Ursids’ peak is strongly

affected by the Moon all night and

this year the prospects are very poor

for this shower.

Geminid meteor shower

The crater Boussingault, named for a

French botanist who lived in the 1800s,

is our target this month. CONSOLIDATED LUNAR

ATL A S/UA/LPL. INSET: NASA/GSFC/ASU

Your best bet to catch the most Geminid

meteors is first waiting for the Moon to set

on the morning the shower peaks.

GEMINID METEORS

Active dates: Dec. 4–17

Peak: Dec. 14

Moon at peak: Waxing gibbous

Maximum rate at peak:

150 meteors/hour

K

N

E

VENUS will sit 5° above Comet

C/2021 A1 (Leonard) on Dec. 17.

The comet may just reach

naked-eye brightness.

OBSERVING

HIGHLIGHT

A

Boussingault