Skywatch - 2021 - 52

NOV E M BE R | 2021

During a total solar eclipse, you can see neat
features like the Sun's hot corona.

e.g., Gianluca Masi's Virtual Telescope
Project (virtualtelescope.eu).
The Demon Star. It's not only the
Sun and Moon that undergo eclipses.
There's a whole class of double stars out
there called eclipsing binaries. The orbital
plane in these systems is oriented at a
relatively low inclination to our line of
sight. As a result, the stars blot out each
other's light as they whip around each
other. One of the most famous of these
stands high in November evening skies.
Meet the Demon Star.
Algol (Beta Persei) is from the Arabic
ra's al-ghūl, which means the demon's
head (see where we got "ghoul" from?).
It's a three-star system, with Algol A and

Nov 18 - 20

29
30

Algol B eclipsing one another and Algol
C orbiting the tighter pair at a larger
distance. Every 2 days, 20 hours, and
49 minutes dimmer Algol B partially
eclipses brighter Algol A; the magnitude
fades from 2.1 to 3.4, after which the
system returns to its original brightness.
The eclipse lasts about 10 hours, but you
don't need to keep watch the whole time!
Algol remains at its dimmest for about
two hours centered on the time at mideclipse, which means you can catch it
near its brightest about two hours before
or after that. There's an easier way: Step
outside and check Algol out when it's at
(or near) its dimmest. Return a couple of
hours later and prepare to be amazed.
Nights in November. While you're
gaping at Algol's brightenings and dimmings, look to another showpiece object,
the Double Cluster. It's in Perseus, but
let's use Cassiopeia to locate it. Extend
the imaginary line from Gamma to Delta
Cassiopeiae about twice the distance
(the chart on page 53 should have "Facing NE" at the bottom) and you'll come
across it easily. It stands out well in binoculars and is a fairly obvious cloud of light
to the naked eye. A telescope will reveal
a pair of star clumps, and you might even
spot a few orange stars in the mix.

Around 8 pm

Pleiades
Moon
Nov 18

18

PERSEUS

Moon
Nov 19

38

Algol

21

TA U R U S
Aldebaran

TRIANGULUM

34

Moon
Nov 20

PLANETS IN
NOVEMBER
Mercury concludes its current, favorable
dawn apparition when it slips from view
around the 11th. However, before then, it
has a couple of notable encounters. On the
3rd Mercury shines at magnitude -0.8, 4½°
left of Spica and just 3° below a thin lunar
crescent. A much more difficult conjunction
to observe is Mercury's close encounter
with Mars on the 10th. Low in morning twilight, descending Mercury passes less than
1° to the left of ascending Mars. You'll likely
need binoculars or a telescope.
Venus is a dominant presence at dusk
all November, gleaming a brilliant magnitude
-4.7 on the 15th. Venus has its monthly
Moon encounter on the 7th when the waxing lunar crescent sits less than 4° to the
planet's lower right. Such pairings are a
reliably lovely sight with just your eyes and in
binoculars, which help bring out the Moon's
"unlit" side, bathed in light reflecting off the
Earth - a phenomenon called "earthshine."
Mars emerges at dawn this month and
will be naked-eye visible after the 22nd.
You should aim your scope at it this morning
when Mars will be just 10′ below the extravagantly named 3rd-magnitude double star
Zubenelgenubi. You'll need an unobstructed
view to the east-southeast.
Jupiter and Saturn remain prime telescopic targets in November, but the clock is
winding down for them. At mid-month, Saturn shines at magnitude +0.6, while Jupiter
is much brighter at magnitude -2.4. On
November 10th, the Moon sits between and
below the planetary pair, and on the following
night, the Moon reaches first-quarter phase
roughly 5° below-left of Jupiter.

10°

2.87 days, Algol dips from its usual
magnitude 2.1 to 3.4 and back. Use this chart to
estimate its brightness in respect to comparison
stars of magnitude 2.1 (Gamma Andromedae) and
3.4 (Alpha Trianguli). The decimals are omitted so
as not to be confused with stars.
ECLIPSE: SEAN WALKER

S Every

Historical Events
ORION
Betelgeuse

the night of the lunar eclipse, the Moon will
be pleasingly placed near the Hyades and the
Pleiades. Even if you don't stay up late enough to
watch the eclipse, you'll nevertheless witness a delightful sight (provided skies are clear, of course).

Rigel

X On

52 SK Y WATCH 2021

Looking East

11/5:
Copernicus
observes a
lunar eclipse
from Rome,
1500

11/9: Captain
James Cook
observes a transit
of Mercury from
New Zealand,
1769


http://www.virtualtelescope.eu

Skywatch - 2021

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