THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
                    "A space for everything and everything in space."

THE DAILY ASTRONOMER
Tuesday, December 15, 2015
December 2015 Night Sky Calendar (Second half)

If one regards the "Daily Astronomer" as a voyage, then within the last 45
days, we've been ploughing the choppy waters around the Cape of Good Hope.
The smooth flow has turned to tumultuous toss; the even keel inverted to
odd oscillation; the constant replaced the sporadic; the reliable has
become the absent; and our cynosure Polaris has precessed down into the
sea. Of course, we are confident that all will be as right as rain again at
least by the turn of the new year! Until then, we brace ourselves against
the onslaught and try to make the best of it.

Toward this end, we offer the second half of the December Night Sky
Calendar. If you're a regular reader, you'll know that the DA posts a
monthly night sky calendar at the beginning of each month. This month, it
was absent and, we're gratified to learn, has been missed. Therefore, we
try to make amends by offering the second half of the December 2015 Night
Sky Calendar.

NOTE: Although we just missed the Geminid Meteor Shower Peak, one can still
observe Geminid Meteors: Watch for a proliferation of Geminds to appear to
emanate from the Castor region tonight. At peak, the Geminid shower can
produce 50 - 100 meteors an hour: a measure called the "ZHR," Zenithal
Hourly Rate. This value equals the number of meteors per hour that a
seasoned observer would see provided the radiant (apparent origin point)
were at the zenith (point directly overhead) in a completely dark sky.
Castor will pass close to our zenith after midnight and remain visible
throughout most of the night. Factoring in light pollution effects, one can
expect to observe perhaps 20 - 40 meteors an hour. The Geminids are unusual
as they are particles cast off by an asteroid, not a comet. The Geminids
parent body is 3200 Phaethon. One might notice that the meteors are quite
bright, but don't leave persistent trains, indicative of their rocky
nature.

FRIDAY, DECEMBER 18: LAST QUARTER MOON

FRIDAY, DECEMBER 18: THE SUN ENTERS SAGITTARIUS

Yes, we do go through this every month. The Sun appears to travel through
thirteen different constellations: those comprising what the astrologers
call "the zodiac," but which astronomers have dubbed "the ecliptic." The
Sun's annual progression through these constellations is illusory. Earth
moves around the Sun and, consequently, the Sun seems to migrate through
thirteen constellations. Today, it leaves Ophiuchus the Serpent Charmer and
enters Sagittarius the Archer. The retinue of ecliptic constellations are
SAGITTARIUS the Archer, Capricornus the Seagoat, Aquarius the Water Bearer,
Pisces the Fish, Aries the Ram, Taurus the Bull, Gemini the Twins, Cancer
the Crab, Leo the Lion, Virgo the Maiden, Libra the Scales, Scorpius the
Scorpion and Ophiuchus the Serpent Charmer. The Sun enters Capricornus on
January 20, 2016.

TUESDAY, DECEMBER 22: WINTER SOLSTICE!

Now, wait a minute! Winter's commencement rates the top medal?! Well, yes,
and despite our sensible aversion to cold, ice, and drear, we confer the
gold onto the winter solstice because it is a solstice, and those events
occur twice yearly. Also, realize that the solstice marks the solar nadir.
Once it attains this low altitude, Sol begins a gradual, but inexorable,
ascent toward the next solstice in June. Were we a bit more astronomically
accurate, we'd refer to this event as the "December Solstice," as winter
begins in the Northern Hemisphere, and summer starts in the Southern
Hemisphere.

WEDNESDAY, DECEMBER 23: MOON 8.6 DEGREES SOUTH OF THE PLEIADES

The gibbous moon veers close to the Seven Sisters. Though the moon appears
quite bright, it won't obscure the star cluster entirely.

FRIDAY, DECEMBER 25: CHRISTMAS FULL MOON

And, this event prompts the question: when was the last time we had a full
moon on Christmas? 1977! When is the next time we'll have a full moon on
Christmas? 2034. So, Christmas full moons aren't exceedingly rare...they
just don't occur that often. Oh, and, for those who really want to know:
the next lunar eclipse on Christmas wont happen until 2531! (Chances are
that some of us won't be around to experience it, but it is utterly
supernatural that we can know it will occur in that year, anyway.)

MONDAY, DECEMBER 28: MOON 5.0 DEGREES SOUTH OF THE BEEHIVE CLUSTER

The Moon is closer to the Beehive Star Cluster (Praesepe) than it was to
the Pleiades, but it will be at a lower illumination percentage (96% on the
23rd as opposed to 88% tonight) so it will still not wholly obscure the
star cluster. See them both in the late evening sky.

TUESDAY, DECEMBER 29: MERCURY AT GREATEST EASTERN ELONGATION (19.7 degrees
from the Sun.)

When at eastern elongation, a planet will be in the western evening sky.
See Mercury low in the western evening sky tonight.

THURSDAY, DECEMBER 31: MOON 1.7 DEGREES SSE OF JUPITER

(The Gold, Silver, and Bronze Event designations will return in the new
year.)

The last astronomical event in 2015 finds the Moon less than two degrees
away from Jupiter. Jupiter and the Moon are two of the night sky's three
brightest objects. Behold them both traveling together across the late
evening sky,

PLANET WATCH

MERCURY: Mercury emerges in the western evening sky by mid month, just
about the time when this half calendar posts. VERDICT: We advise you to
search for Mercury late in December, around the time it reaches greatest
eastern elongation.

VENUS (PICK PLANET): has been diminishing in brightness since August, but
remains brighter than all the other planets. Venus remains the predominant
planet in the early morning sky. VERDICT: Oh, seize every opportunity to
observe the brilliant planet, Venus. Remember, Venus will remain in the
pre-dawn eastern sky until April. Then it will vanish until late July
before emerging in the western evening sky.

MARS: has been gradually brightening since September, but it is dimmer than
the other naked eye planets, including Saturn. Mars will continue to
brighten dramatically throughout the first part of 2016 until it reaches
opposition on May 22. At this time, it will be just about as bright as
Jupiter! VERDICT: Mars isn't a spectacle, yet, but still a moderately
bright planet that one can see in the early morning eastern sky.

JUPITER: isn't nearly as bright as Venus, but is still brighter than all
the night sky stars. Jupiter's brightness is increasing as it approaches it
March 8th opposition. Jupiter is the "beta" morning sky planet along with
"alpha" Venus and "gamma" Mars. VERDICT: Heavens! Three morning sky
planets! Why bother sleeping at all?!

SATURN: returns to the morning sky by mid month, thus ending its month long
hiatus. This gorgeous ringed world is just visible in the pre-dawn sky.
Watch Saturn brighten gradually and rise progressively earlier as it
approaches its June 3, 2016 opposition. VERDICT: Saturn is a rather
difficult object to observe presently. Better to wait until later this
winter, when it rises higher into the morning sky.

PLANETS IN ORDER OF DECREASING BRIGHTNESS

VENUS - JUPITER - MERCURY - SATURN- MARS
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