Astronomy

Dec 1^6

11

16

21

26

31

Path of Laetitia

N

E

0.5°

CETUS

b

84

NGC 1055

M77

Cruising by a whale of a galaxy

Daytime drama for the Moon and Venus

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WWW.ASTRONOMY.COM 43

A small space rock could trigger

some excitement among astro-

imagers when it passes close

to the popular galaxy M77. On

December 9 and 10, asteroid

39 Laetitia poses as a 10th-

magnitude star on the fringe of

this bright spiral, mimicking the

light from a supernova nearly

50 million light-years away.

M77 is the founding member

of Carl Seyfert’s class of active

galaxies. Hidden from view by

gas, dust, and dense swarms of

stars, the galaxy’s core harbors a

supermassive black hole busily

devouring its surroundings.

You can pick up Laetitia and

M77 with a 4-inch telescope

from a dark site or an 8-inch

instrument from the suburbs.

The pair lies less than 1° east-

southeast of 4th-magnitude

Delta (δ) Ceti. Bump up the

power past 100x, let yourself

dark adapt a bit, and you

should see three other faint

fuzzies nearby, all part of the

M77 group of galaxies.

To the eye, Laetitia will not

move enough to notice during

a single viewing session. When

it’s near M77 or between Delta

and the spiral galaxy NGC 1055,

make a quick sketch of the field

and return to it the next clear

night. The object that has

shifted position is the asteroid.

LOCATINGASTEROIDS

An asteroid poses as a distant supernova

and then its brighter disk cross
the jovian cloud tops.
The angle of the Sun shin-
ing on Jupiter diverges notice-
ably from our line of sight
during December. You can get
a good idea of the difference
December 8. Callisto’s shadow
falls on Jupiter’s northern
hemisphere starting at 4:17 a.m.
EST when the moon itself is
still 1.6' (nearly three Jupiter-
widths) east of the planet.
Europa, the target of
NASA’s next major planetary
mission, casts its shadow on
Jupiter’s cloud tops early on
the mornings of Christmas
Eve and New Year’s Eve for
observers in the Americas. On
both days, Europa’s shadow
starts crossing the jovian disk
about 2.5 hours before the
moon itself.
The two planets that hud-
dled with Jupiter in eastern
Leo early last month string
out across neighboring Virgo
in early December. First to
rise is Mars, which comes up
nearly two hours after Jupiter.
On the 1st, the Red Planet
shines at magnitude 1.5 and
stands 1.5° due south of mag-
nitude 2.8 Gamma Virginis,
the constellation’s second-
brightest star. Mars’ orange
hue contrasts nicely with
blue-white Spica, Virgo’s
1st-magnitude luminary,
which lies some 14° southeast.

Mars tracks eastward during

Decem ber and passes 4° north

of Spica on the 21st.

The planet remains on the

far side of the solar system

from Earth and thus still

looks tiny: a mere 5" across.

At this size, only observers

with large scopes can hope to

pick up subtle surface details.

Mars will grow much bigger,

brighter, and more detail-rich

next spring as it approaches

opposition in late May.

Venus rises about an hour

after Mars on December 1

and appears conspicuous in

the eastern sky by 4 a.m. local

time. At magnitude –4.2, it is

five full magnitudes (a factor

of 100) brighter than its com-

panion Spica, which stands

just 4° away. Venus moves

quickly this month, crossing

into Libra on the 11th. Look

for the magnitude 2.8 double

star Zubenelgenubi (Alpha [α]

Librae) 2° south of Venus on

the 17th.

The rapid changes to

Venus’ telescopic appearance

this autumn slow considerably

in December. The apparent

size of its disk shrinks from

17" to 14" while its gibbous

phase fattens from 67 to 77

percent lit.

If you’re observing the

morning of December 7, you’ll

no doubt notice the waning

crescent Moon closing in on

Ve nu s. A f t e r s u n r i s e , L u n a

passes directly in front of

(occults) the planet for viewers

across North America. You can

follow this occultation through

binoculars or a telescope.

The time when Venus dis-

appears behind the Moon’s

sunlit limb depends on your

location. The following are

accurate to the nearest minute

for several cities across the

country: Seattle at 7:54 a.m.

PST; Los Angeles at 8:04 a.m.

PST; Denver at 9:36 a.m. MST;

Houston at 11:12 a.m. CST;

Chicago at 11:18 a.m. CST;

New York at 12:42 p.m. EST;

Boston at 12:43 p.m. EST; and

Miami at 12:52 p.m. EST. If

you want to view the event

through a telescope, be sure

to set up at least 30 minutes

before these times.

On June 18, 2007, Earth’s satellite passed in front of Venus during daylight
hours. North American observers can witness a similar event December 7.

The 10th-magnitude asteroid Laetitia skirts north of the bright galaxy

M77 in Cetus the Whale during the second week of December.

ANTHONY AYIOMAMITIS