THE SOUTHWORTH PLANETARIUM
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43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded
January 1970
2021-2022: LIII
"The mind that is anxious about the future is miserable."
-Seneca


THE DAILY ASTRONOMER
Monday, December 6, 2021
December 2021 Night Sky Calendar Part III

*TUESDAY, DECEMBER 14, 2021: GEMINID METEOR SHOWER PEAKS*
In order to discuss the Geminid meteor shower, we should first mention a
remarkable little celestial body called 3200 Phaeton. Discovered in 1983,
Phaeton is an *Apollo asteroid*, or one that crosses Earth's orbit.* Even
by the standards of Apollo asteroids, it is highly unusual. Not only does
it veer closer to the Sun than any named asteroids (13 million miles from
the Sun, about 1/3 of Mercury's mean distance), but it might well be a
"dead comet," or one that has depleted its surface ices so as to expose a
rocky inner core. As this extinct comet approaches the Sun, the intense
heat and solar pressure wicks away this core material, much as wind erodes
desert sand. The detached particles form a tail reminiscent of a dust tail
which follows in a comet's wake. These particles constitute the meteoroids
responsible for the Geminid meteor shower. Consequently, the Geminid meteor
shower 's parent body is asteroidal, not cometary. Almost all meteor
showers originate from comets.

The Geminid meteor shower begins on December 4, ends on December 17th and
peaks on December 14th. At peak, this shower produces about 80 bright,
medium-speed meteors an hour. These meteors appear to originate within the
constellation Gemini, hence the name. The graphic below shows the radiant's
location close to Castor, the star representing the head of the northern
twin of the same name.

[image: Geminids_Art_725x572.jpg]
The Geminid radiant is located within Gemini, the zodiacal constellation to
the northeast of Orion. Image credit: Astronomy Now.

While one can watch for Geminid meteors throughout the night, it is best to
watch after midnight, the time when our part of the planet is moving into
the path of the meteoroid stream.

*THURSDAY, DECEMBER 16: MOON NEAR PLEIADES STAR CLUSTER*
The waxing gibbous moon (94% illuminated) appears close to the Pleiades
Star Cluster, a galactic cluster within the constellation Taurus the Bull.
Although the gibbous moon is quite bright, one will still be able to
observe the Pleiades, or Seven Sisters, within the same vicinity.

*SATURDAY, DECEMBER 18: FULL MOON*
A micr0-moon! Ok, well, what is a "micro-moon?" A micro moon is a full moon
that occurs when the moon is full around the time of apogee, the point of
greatest distance in the moon's orbit. As the moon reached apogee
yesterday, we can consider this full moon to be a micromoon.

*TUESDAY, DECEMBER 21: WINTER SOLSTICE (GOLD EVENT!!!)*
At 10:59 a.m. Eastern time, astronomical winter begins! Earth is tilted on
its axis by 23.5 degrees relative to its orbital plane. Consequently, as
Earth revolves around the Sun, the poles continually change alignments
relative to it. When we reach the summer solstice, the north pole is
directed toward the Sun to its greatest extent. When we reach the winter
solstice, the south pole is aligned toward the Sun, while the north pole is
directed away from it.

[image:
Typical-diagram-illustrating-the-cause-of-seasons-in-the-northern-hemisphere.png]

When at an equinox, neither pole is directed toward the Sun more than the
other.       After reaching the winter (December) solstice, Earth will
continue to move along its orbit so that the north pole will start to move
back toward the Sun again.

[image: images.png]

On Earth, we observe this shifting as the changing altitude of the Sun.
 On the winter solstice, the Sun follows its shortest path through the
sky.    On the summer solstice, its path is longest.   Throughout the year,
the Sun's path vacillates between these two extremes.     This change
affects our weather profoundly because the Sun heats the ground,which then
warms the surrounding air.        When the Sun's angle is lower, it heats
the ground less efficiently than it does when it is at a higher alttitude.

Winter now begins in the northern hemisphee.
Summer begins in the southern hemisphere!

Final part of the calendar tomorrow.


*More precisely, an Apollo asteroid's semi-major axis (mean distance) is
greater than Earth's, but perihelion distances less than that of Earth. A
perihelion distance is a celestial body's point of least distance from the
Sun. Apollo asteroids are named after the asteroid 1862 Apollo.


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