THE SOUTHWORTH PLANETARIUM
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Altitude:  10 feet below sea level
Founded January 1970
Julian Date: 2458820.16
                "Heavens above!"

THE DAILY ASTRONOMER
Monday, December 2, 2019
December 2019 Night Sky Calendar   Part I


What's happening in December!
Well, what ISN'T happening.  This month, astronomical winter begins, the
Geminid meteor shower peaks, we bid adieu temporarily to Jupiter, the moon
swings by three planets, Venus appears to nudge close to Saturn, the Long
Night Moon describes a wide arc over our crystallines snowscapes, the Sun
will start to set later each night and one never knows if an aurora
borealis will bedazzle our skies.


*THURSDAY, DECEMBER 4:  FIRST QUARTER MOON*
"First Quarter" is a curious term applied to this lunar phase.  It implies
that we see only one quarter of the moon's "facing area,"  the region of
the moon directed toward Earth.   Instead, we see half of the "facing area"
at first quarter.    The term refers to the first quarter of the moon's
orbit.  After a new lunation cycle begins at new moon, or conjunction, the
moon must complete one quarter of its orbit to attain the first quarter (or
quadrature) position.    At this time, we see it as a "half moon."

*FRIDAY, DECEMBER 5:  MOON AT APOGEE*
Yes, we know what Ptolemy said.  In his elaborately designed, brilliantly
conceived, yet utterly incorrect model, the planets and the moon all
revolve around Earth along perfectly circular orbits.  He derived his
notion of circular orbits from the Greek idea that the sky was an
exquisitely beautiful and timeless realm in which all the empyreal orbs
described perfect orbits.  Even though Copernicus properly placed the Sun
in the solar system center, he retained the circular orbits because a. they
seemed to move that way and b. he was a political pragmatist who realized
that kicking the hornet's nest twice was slightly more problematic than
doing it once.
Kepler, who actually coined the term "orbit," was the first to accurately
describe the planetary and lunar paths as elliptical, meaning that their
distance from the parent body wasn't constant, but changed constantly:
veering from a minimum to a maximum.   The moon's minimum distance is
called "perigee," while the maximum is known as "apogee."    Today, the
moon reaches "apogee," and will be 404,446 kilometers from Earth at the
precise apogee moment.   As the moon is at such a far distance around the
time of first quarter, we can expect tides to be lower.  Apart from this
effect, nothing unusual should occur as a consequence of this lunar apogee.

*TUESDAY, DECEMBER 10:  MOON NEAR PLEIADES*
One will barely see the Seven Sisters "close" to the nearly full moon (97%
illuminated) tonight.   The Pleiades Star Cluster is the night sky's
brightest (but not the closest) star cluster.*
As it appears so luminous, this cluster will remain visible despite the
gibbous moon's close proximity.     Now that we're veering precariously
close to astronomical winter, the Pleiades Star Cluster will remain visible
all night long.   Those who experience difficulty in locating it, should
look to the moon tonight as a guide to finding it.

*THURSDAY, DECEMBER 11: VENUS 1.8 DEGREES SOUTH OF SATURN (BRONZE EVENT!)*
One will find the brightest planet and the most distant naked eye planet
apparently close together in the western evening sky tonight.
 Distinguishing between these two worlds will prove quite easy, as Venus
(magnitude -4) will be 70 times brighter than Saturn (magnitude 0.6)
Both planets will set just after 6 p.m.

*FRIDAY, DECEMBER 12: FULL MOON*
The long night moon, so named because the nights are longest this time of
year.  Also, the full moon close to the winter solstice follows the longest
path of any full moon during the year.  When the moon is full around the
winter solstice, it moves along an arc the Sun describes on the summer
solstice. Conversely, when the moon is full around the summer solstice, it
moves along the sun's winter solstice arc.    As the Sun remains above the
horizon for more than 15 hours on the summer solstice, the winter's first
full moon will also be visible for the same amount of time.


*The closest is the Hyades Star Cluster at a mean distance of 153 light
years.  The Pleiades Star Cluster's mean distance is 445 light years.


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