Astronomy

ORION

URSA

MAJOR

AURIGA

GEMINI

TAURUS

LEO

Procyon Rigel

Betelgeuse

Aldebaran

Capella

Radiant

Castor

Pollux

December 14, 1 A.M.

Looking high in the south 10°

Regulus

Geminid meteor shower

Hop aboard the polar express

WWW.ASTRONOMY.COM 37

RISINGMOON

METEORWATCH

Whether Santa Claus delivers a

new telescope or you use just

your naked eyes, marvel at the

Full Moon high in a late evening

sky December 25. Chances are

you’ll feel there’s something

unusual about it. You’re right.

Mare Crisium on the eastern

limb looks like it’s nearly on

the equator, and if you view

through binoculars, the rays

pointing back to Tycho reach

near the southern limb. Plenty

of “extra” light-hued terrain also

appears near the north pole.

On the 25th, Luna lies about

as far south of the ecliptic —

Earth’s orbital plane around the

Sun — as it can get. From our

earthbound perspective, we see

a little past the north pole and

down the farside in what astron-

omers call a northern libration.

If you’re up for a little adven-

ture, let’s embark on a trek to

the north pole.

Lunar cartographers named

many features close to the pole

after great polar explorers of

past centuries. Two major cra-

ters honor the American adven-

turers Richard Byrd and Robert

Peary. Like those pioneers, avoid

eyestrain by using sunglasses or

a filter to cut down on the Full

Moon’s glare. Look just below

the northern limb for Byrd,

which appears as a large, flat,

and fully illuminated oval.

On the 25th, sunlight nicely

illuminates this crater’s back wall,

which is almost indistinguishable

from Peary’s southern flank. The

shadows help our minds gener-

ate a 3-D view of the polar

regions. We can see over and

past Peary’s parapets into its

partially shadowed floor right

up to the back wall. Immediately

behind that lies the north pole

itself, which remains in shadow.

If you look carefully beyond

Peary, you’ll see another lit

wall. This is the outer rim of

Rozhdestvenskiy, a large crater

named for Soviet physicist

Dmitriy Rozhdestvenskiy. This

feature lies at 87° north latitude

on the lunar farside. Off to the

east and down the limb a little

ways, you’ll find the crater walls

of Nansen, named for the

Norwegian polar explorer

Fridtjof Nansen.

Meteor observers always look at

the calendar to see which showers

will occur near New Moon. Bright

moonlight drowns out fainter

meteors and renders the brighter

ones less impressive. But no wor-

ries this month — the prolific

Geminid shower peaks December

14, just three days after New Moon.

The “shooting stars” appear to

radiate from a point near Castor in

Gemini. The radiant climbs higher

in the east throughout the evening

and passes nearly overhead around

2 A.M. local time. Don’t stare at the

radiant, however — you’ll see lon-

ger streaks if you look 40° to 60°

away. For the best views, find an

observing site far from the city,

where you can expect to see up

to 120 meteors per hour.

A Christmas present at Luna’s north pole

Absent Moon means magical meteor show

— Continued on page 42

Geminid meteors

Active dates: Dec. 4–17

Peak: December 14

Moon at peak: Waxing crescent

Maximum rate at peak:

120 meteors/hour

you might not be able to iden-
tify it unambiguously. To con-
firm a sighting, point your
telescope at the suspected
planet. Neptune will show a
disk that measures 2.3" across
and sports a blue-gray color.
Head 40° east of Neptune
along the ecliptic — the
apparent path of the Sun
across the sky that the planets
follow closely — and you’ll
reach Uranus. This ice giant
world, a kissing cousin to
Neptune, resides among the
faint stars of Pisces the Fish.
Uranus appears slightly more
than halfway to the zenith in
the southeast as darkness
falls and remains on view all
evening. It doesn’t set until
around 1 a.m. local time even
as the month comes to a close.
The seventh planet shows
up easily through binoculars.
Glowing at magnitude 5.8,
it is technically visible with
naked eyes under a dark sky,

One of this year’s most prolific meteor showers could deliver up to 120

“shooting stars” per hour under ideal conditions.

A favorable libration at Full Moon brings normally hidden craters at the

lunar north pole into view. ALISTER LING, BASED ON CLEMENTINE DATA; INSET: NASA/GSFC/ASU

A waning crescent Moon passes directly in front of Venus during

daylight hours December 7 for observers across North America.

OBSERVING

HIGHLIGHT

N

E

Peary

Byrd