THE SOUTHWORTH PLANETARIUM
70 Falmouth Street      Portland, Maine 04103
(207) 780-4249      usm.maine.edu/planet
43.6667° N    70.2667° W
Founded January 1970
2022-2023: LIV
Sunrise: 7:05 a.m.
Sunset: 4:04 p.m.
Civil twilight begins: 6:33 a.m.
Civil twilight ends: 4:37 p.m.
Sun's host constellation: Ophiuchus
Moon phase: Waning Gibbous (83% illuminated)
Moonrise: 8:00 p.m.
Moonset: 11:12 a.m. (12/13/2022)
Julian date: 2459926.21
"People who say it cannot be done should not interrupt those who are doing
it." -George Bernard Shaw


THE DAILY ASTRONOMER Monday, December 12, 2022
December 2022 Night Sky Calendar Part I

Yes, we're finally starting the December 2022 Night Sky Calendar, which is
convenient timing now that we're almost in mid-December. This truncated
calendar will be offered in two parts.

*FRIDAY, DECEMBER 9:  DATE OF EARLIEST SUNSET*
Although the duration of daylight is shortest on and around the winter
(December) solstice, the dates of earliest sunset do not correspond
precisely with the solstice.  In fact, these dates vary with latitude.
 As we can see in the graphic below, the date increases with increasing
distance from the Equator. (Note: the daylight duration on the equator is
12 hours every day of the year.)     While the earliest sunset in Miami
occurs on November 30th, the earliest sunset in Southern Maine occurs on
December 9th.     The sunset time on 12/9 in Portland is 4:04 p.m.      The
sunset time remains the same for the next few days until December 14th,
when the sun sets at 4:05 p.m.   During the intervening dates, the sun set
time increases by a matter of less than 10 seconds each day.

[image: earliest-sunset-stephen-aman.jpg]

One might wonder:  if the shortest "day" is on the winter solstice, how can
the earliest sunrise occur earlier?   It's simple.    The sunrise times
will continue to increase until early January.    On January 2nd, the sun
rises at 7:15 a.m. in Portland. For the next few days, the sun rises at
7:15 a.m.   On January 6th, the Sun will rise at 7:14 a.m.

For  mid-latitude Northern Hemisphere observers, the sequence is as follows:


   - *Earliest sunset*:   early/mid December
   - *Shortest day:*  winter (December) solstice
   - *Latest sunrise*:  early January

For mid-latitude Southern Hemisphere observers, the sequence is:


   - *Earliest sunrise:*  early/mid December
   - *Longest day:*   summer (December) solstice
   - *Latest sunset:   * early/mid January

The latest sunrise, earliest sunset and winter solstice would occur on the
same day if Earth's orbit were perfectly circular and if the planet were
not "tilted" relative to the plane of that orbit.     However, because
Earth's orbit is elliptical, its distance from the Sun and, consequently,
its orbital velocity, is never constant.     When Earth is closest to the
Sun (Northern Hemisphere winter), it appears to move more quickly along the
sky than it does when further away (Northern Hemisphere Summer).   Also,
the tilted axis draws the Sun along different arcs throughout the year, so
its pathway will vary.

If you're eager for longer days, take solace on December 9th.  After that
date, the Sun will start setting progressively later each day.

*WEDNESDAY, DECEMBER 14: GEMINID METEOR SHOWER PEAKS (SILVER EVENT!!)*
Meteors are mesospheric events, meaning that they generally occur high in
the Mesosphere, between 75 - 100 kilometers above Earth's surface.   This
altitude is just at or below the Karman Line (100 km) that marks the
official boundary of outer space.   Meteors are the lights we see when
meteoroids infiltrate our upper atmosphere.   The meteoroid heats up as it
descends and excites the nearby atmospheric atoms, meaning that the
electrons within them are elevated to higher energy states.  When the
electrons revert to their previous states, they emit the photons we
perceive as "meteors."

Meteor showers are named for the constellation from which the meteors
appear to emanate.    The Geminid meteors appear to come out of the
constellation Gemini.    One can best see these meteors after midnight,
when our part of the planet is turning into the densest part of the meteor
stream.

Ordinarily, one would be able to see about 30 - 40 meteors an hour from
this shower.     The waxing gibbous moon (67% illuminated) will interfere
somewhat as it rises at 10:08 p.m.

[image: unnamed.jpg]

*FRIDAY, DECEMBER 16:  LAST QUARTER MOON*

*WEDNESDAY, DECEMBER 21:  MERCURY AT GREATEST EASTERN ELONGATION (20
DEGREES)*
Mercury watchers rejoice!  Tonight, you'll be able to snatch a glimpse of
this  elusive little planet in the western evening sky.  Note:  when a
planet is at greatest eastern elongation, it will appear in the western
evening sky.   Conversely, when the planet is at greatest western
elongation, one will find it in the eastern pre-dawn sky.

*WEDNESDAY, DECEMBER 21:   WINTER SOLSTICE (GOLD EVENT!!!)*
At 4:47 p.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 altitude.

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



To subscribe or unsubscribe from the "Daily Astronomer"

http://lists.maine.edu/cgi/wa?A0=DAILY-ASTRONOMER