Skywatch - 2021 - 56

DECE M BE R | 2021
These are just a tiny fraction of the
cataclysmic consequences of too much
human-created light. A groundbreaking
study published in 2016 reported that a
whopping 80% of the world's population lives under skyglow, the eﬀect of the
sky's brightening in inhabited areas, and
a jaw-dropping 99% of Americans and
Europeans can't readily enjoy the experience of a naturally dark night. There are
some things you can do to mitigate these
eﬀects, for example, by asking yourself
if you need to keep your front porch
light on all night long. And if the answer
is "yes", consider shielding its bulb, or
choosing one that pours out less light.
Several organizations exist whose sole
purpose is to raise awareness of and combat light pollution. The most prominent
is the International Dark Sky Association (darksky.org). Go to its website
for more tips on what you can do or how
you, too, can help mitigate this scourge.
December delights. Did you know
you can spot the Crab Nebula from
your backyard? And you won't need the
Hubble to see it. Of course, it won't look
like much more than a smudge, but just
think: You're seeing the remnants of a
supernova explosion with your very own eyes.
Locating the Crab is the easy part: Train

your scope on Zeta Tauri, the star that's
the tip of the Bull's eastern horn, then
sweep roughly 1° northwest. You should
detect the nebula as a small, hazy patch.
In ideal, non-light-polluted conditions,
the Crab can be glimpsed in binoculars,
but a telescope is better. At lower magnifications the nebula smudge fits in the
same field of view as the star; with higher
magnification the Crab morphs into a
faint oval of light, longer than it is wide.
But a really big telescope with plenty of
magnification will start to reveal hints of
the network of delicate tendrils that you
see in the images on page 54.
On the evening of December 18th, the
Moon is full - and it's one day past apogee. So return to the spot where you witnessed the full Moon back in May when
it was close to perigee (but you'll have to
face the east-northeast now). Do you see a
diﬀerence? Probably not. But that doesn't
mean you can't enjoy the last full Moon
of the year - it's pleasingly framed by
Aldebaran, Capella, Castor and Pollux,
and Betelgeuse, all familiar names from
this past year of discovering the night sky.
Whether you're marveling at views of
the Crab Nebula through a telescope or
oohing-and-aahing at the Moon, remember: There's plenty to see - enjoy.

Dusk, Dec 6 - 8

Dawn, Dec 30 - 31

45 minutes after sunset

1 hour before sunrise

Moon
Dec 8

Saturn

Moon
Dec 30
Moon
Dec 7

CAPRICORNUS

Venus

Moon
Dec 31
10°

Moon
Dec 6

S Left:

Mars

Looking Southeast

Saturn, Venus, and the waxing crescent Moon make for a pretty sight after sunset at the start of
the month. Right: Bid 2021 farewell with a lovely view of the thin sliver of the crescent Moon, Mars, and
Antares - you'll have to get up before the Sun does, but you'll be richly rewarded.
56 SK Y WATCH 2021

Mercury remains out of view most of
December, returning to the evening sky after
the 24th. By the 31st the swift little planet is
relatively well placed, shining at magnitude
-0.7 and setting 1¼ hours after the Sun.
Venus is climbing higher and getting
brighter. On December 3rd it reaches its
greatest altitude for observers at mid-northern latitudes. Soon afterwards, on the 6th,
it's joined by the crescent Moon, which sits
just 3° below the Evening Star. On the 9th,
Venus reaches maximum brightness and
gleams a startling magnitude -4.9. That
luminosity peak represents an appropriate
ﬁnal hurrah for the planet's 2021 apparition.
Mars is gradually lifting itself out of
morning twilight. As December opens, it
clears the east-southeast horizon 1½ hours
before the Sun, and stretches that ﬁgure to
a full 2 hours by month's end. At magnitude
1.6, Mars is a far cry from the magnitude
-2.6 brilliance it attained when it was near
Earth in October 2020. You'll have to wait
until December 2022 before the Red Planet
and Earth are close again.
Jupiter and Saturn adorn the early evening sky and form an attractive threesome
with Venus all month. The trio are strung out
in a line, and on the 4th are equally spaced.
On the 7th, the Moon sits roughly 5½° below
Saturn, and a bit more than 7° below Jupiter
the following night. At mid-month, both planets transit the meridian well before sunset.
Saturn sets shortly after 8 p.m., followed by
Jupiter a little after 9:30 p.m. For detailed
telescopic views, you need to get busy as
soon as twilight begins to fade and catch the
planets while they're still relatively high.

SCORPIUS

Antares

Looking South-Southwest

PLANETS IN
DECEMBER

Historical Events
12/3: Pioneer
10 makes
the fi rst
spacecraft
flyby of
Jupiter, 1973

12/5: Nicolas
Louis de Lacaille
discovers
NGC 2070,
the Tarantula
Nebula, 1751

http://www.darksky.org

Skywatch - 2021

Table of Contents for the Digital Edition of Skywatch - 2021