2019-12-01_Astronomy

WHEN TO

VIEW THE

PLANETS

EVENING SK Y

Venus (southwest)

Jupiter (southwest)

Saturn (southwest)

Uranus (southeast)

Neptune (south)

MIDNIGHT

Uranus (west)

MORNING SK Y

Mercury (southeast)

Mars (southeast)

42 ASTRONOMY • DECEMBER

5°

December 28, 1 hour after sunset

Looking southwest

CAPRICORNUS

Venus

Moon

The Moon’s dramatic meeting with Venus

A slender crescent Moon bathed in earthshine rises up to greet the sky’s
brightest planet during 2019’s final week.

COMET SEARCH I A visitor receives a Hero’s welcome

COMET PANSTARRS

(C/2017 T2) strikes two notable

poses in December as it continues

its nine-month tour of the polar

sky. Researchers discovered this

comet as a 20th-magnitude fuzz-

ball in October 2017 while survey-

ing the sky with the Pan-STARRS1

Telescope on Haleakala in Hawaii.

Astronomers expect it to glow at

9th or 10th magnitude this month.

PanSTARRS spends most of

December among the background

stars of Perseus the Hero, a region

that passes nearly overhead during

the evening hours. If you have clear

skies, haul out a 4-inch or larger tele-

scope on the 14th or 15th and target

the star cluster NGC 1528. C/2017 T2

shares a low-power field of view

with the cluster both evenings. You’ll

need to boost the magnification quite a bit to see detail in the compact but high-surface-brightness comet.

The second photo opportunity comes the weekend of December 21 and 22. The comet then appears to

drift across the face of the sprawling emission nebula Sharpless 2–205. Think of the nebula as a fainter sibling

to the more famous Heart and Soul nebulae in Cassiopeia. PanSTARRS will pass near that pair in January.

The comet remains on the inbound leg of its elongated orbit around the Sun. Astronomers expect it to

reach 7th or 8th magnitude at its closest approach in May 2020.

This cosmic interloper could reach 9th magnitude as it skirts the

boundary between Perseus the Hero and Camelopardalis the Giraffe.

1°

PERSEUS

CAMELOPARDALIS

h

_

b

+

Sharpless 2–205

Path of

Comet PanSTARRS

Dec 1

6

11

16

21

26

31

NGC 1528

N

E

Comet PanSTARRS (C/2017 T2)

Fortunately, Neptune rides 45°

above the southern horizon as

twilight fades to darkness and

doesn’t set until near midnight

local time.

The planet resides in the

same binocular field as 4th-

magnitude Phi (φ) Aquarii. On

December 1, Neptune lies 1.5°

west-southwest of this star.

Look for a 7th-magnitude field

star 0.9° due west of Phi. The

planet forms an isosceles tri-

angle with these two stars.

Neptune moves slowly east-

ward relative to the starry back-

ground during December. By

the 31st, it has closed to within

1.1° of Phi. If you have a hard

time identifying the planet,

target your suspect with a tele-

scope. Only Neptune shows a

disk, which appears 2.3" across

and blue-gray in color.

Uranus proves to be an eas-

ier target. Not only does this

planet shine brighter than

Neptune, at magnitude 5.7, but

it also appears higher in the

sky. Uranus lies in the south-

east after darkness falls and

climbs 60° above the southern

horizon around 9:30 p.m. local

time in early December. It

reaches the same position two

hours earlier by month’s end.

The planet lies in a sparse

region of southern Aries, near

the Ram’s border with Pisces

the Fish. Although it’s bright

enough to be an easy target

through binoculars, the lack

of nearby guide stars makes it

tricky to pinpoint.

Start with the Ram’s bright-

est star: magnitude 2.0 Hamal

(Alpha [α] Arietis). Then locate

magnitude 3.8 Alrescha (Alpha

Piscium) 21° due south of

Hamal. If you draw an imagi-

nary line between these two

stars, you’ll find Uranus about

1° from the midpoint in the

direction of Alrescha.

Although Uranus has about

the same physical size as

Neptune, it lies 1 billion miles

closer to Earth, or a bit less than

two-thirds as far away. Do the

math, and you’ll find Uranus

should appear slightly more

than 50 percent larger when

viewed through a telescope. It

does — Uranus spans 3.7" this

month, and its disk sports a

delightful blue-green color.

The night sky’s final two

planets don’t emerge until the

approach of dawn. Mars appears

first, rising around 4:30 a.m.

local time December 1. The Red

Planet shines at magnitude 1.7

near the western edge of the

constellation Libra. About an

hour later, Mercury rises against

SKY THIS MONTH

94 

The peak percentage of the Sun’s area the

Moon hides during the December 26 eclipse.

— Continued from page 37