THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Founded January 1970
Julian date: 2457707.16 (see "From the Catacombs of Infinite Knowledge")
"One night at a time."
*THE DAILY ASTRONOMER*
*Monday, November 14, 2016*
*Week 11 Night Sky Calendar*
If last week's night sky calendar had been a casual stroll through a
perfumed garden, this week's will be a desperate sprint through a perilous
labyrinth. The night sky is roaring on all eight cylinders and we are
determined to keep up with it. (Truth be told, we never do, actually.
The sky, much like the Universe beyond it, changes ceaselessly and
continously in every direction for a thousand different reasons and if we
could keep up with every chance conjunction, errant meteor, auroral oval
expansion, and the myriad other spectacular celestial events, each DA
would be a burdensome, 20,000 word disaster sent to less than one
subscriber.)
Of course, this calendar is not quite as long as it would have otherwise
been had we not devoted Thursday's DA to Monday's super moon. All the
same, we have a lot to do today, so off we go!
MONDAY, NOVEMBER 14: SUPER MOON (PLATINUM EVENT)
Today, the moon will be closer to Earth than it has been since 1948. That
this close approach coincides with the full moon will give us a super moon
worth watching. This super moon will be 14% larger and 30% brighter than
an apogee full moon: a full moon that occurs when the moon is at its
greatest distance from us. For more information about this uber-super
moon, please refer to the DA article posted on Thursday, November 10.
The forecast for Monday is dicey, so we cannot assure you that you will see
this super moon. However, we'll have yet another in December, albeit
slightly less dramatic.
TUESDAY, NOVEMBER 15: MOON 9.0 DEGREES SOUTH OF THE PLEIADES
The moon will be 98% illuminated tonight and will therefore resemble a full
moon. Though quite bright, the moon will not completely obscure the
gorgeous galactic star cluster poised on Taurus the bull's shoulder.
When the nearly full moon appears to pass close by the Pleiades, one knows
that winter is imminent.
TUESDAY, NOVEMBER 15: MOON 0.45 DEGREES NORTH OF ALDEBARAN
If the moon appears near the Pleiades, it should also appear close to
Aldebaran, the brightest star in Taurus the bull. The moon will, indeed,
move close Aldebaran in our sky tonight. It will be so close that the
moon will occult Aldebaran from locations in the Eastern Hemisphere. An
occultation occurs when the moon passes directly in front of a more distant
celestial object. Such occultations are quite common. Less common are
occultations of bright stars. Only four first magnitude stars (Aldebaran.
Antares, Regulus and Spica) are close enough to the moon's orbit to ever be
occulted by it.
THURSDAY, NOVEMBER 17: LEONID METEOR SHOWER PEAKS (GOLD EVENT!!!)
What is a meter shower? Simply. a meteor shower occurs when Earth moves
through a stream of particles emitted by either a comet or an asteroid.
For instance, as a comet approaches the Sun, its upper ice layers
sublimate and release vast quantities of dust and other impurities that had
been trapped within them. These particles, called "meteoroids, remain
suspended in space along a region centered on the parent body's orbit.
When Earth passes through this cloud, many meteoroids will descend through
the atmosphere. The meteoroids excite the atmospheric atoms in their path.
(The electrons within the atoms are elevated into higher energy levels.)
The electrons settle down into their original energy orbits and, in so
doing, emit the photons that produce the light we see as meteors.
*The Leonids' Radiant. ** Meteor showers are named for the
constellation*
*from which the meteors appear to emanate. The Leonid meteors appear to
shoot*
*out of Leo the Lion. Were one to 'track' these meteors, one would notice
that*
*the paths converge within this constellation. Image: Stardate.org*
The Leonid meteor shower consists of meteoroids emitted by Comet
Tempel-Tuttle, a short period comet that reaches perihelion-closest point
to the Sun- every 33 years. (For this reason, the Leonid shower stream is
abundantly replenished every 33 years.) The meteors appear to emanate
from the constellation Leo, hence the name, "Leonids." The shower
technically begins on November 6th, when Earth enters the vast region of
Leonid meteoroids. We leave this stream on November 30th. The shower
peaks on November 17th, when our planet pushes through the densest area of
this stream "cloud."
*Shower from above. This 1997 NASA image shows Leonid meteors high in
Earth's atmosphere. *
An observer will see 20 - 30 meteors an hour tonight, provided the sky
conditions are favorable. The best time to observe a meteor shower is
after midnight, when our part of the planet moves into the meteoroid
stream. However, tonight the moon will be 86% illuminated and will rise
before 8:00 p.m. The moon will be bright and up throughout the rest of the
night, making seeing more difficult than usual.
SATURDAY, NOVEMBER 19: MOON 3.9 DEGREES SOUTH OF BEEHIVE CLUSTER
The Beehive Star Cluster is the one prominent feature in the zodiacal
constellation Cancer the Crab. Tonight, the waning gibbous moon (67%
illuminated) will appear to pass just to the south of this cluster.
(We'll visit the Beehive Star Cluster in Tuesday's DA as part of our annual
Messier tour.)
*PLANET WATCH*
*MERCURY (Host constellation: Libra)*
Mercury is not visible until late November, when it will emerge in the
western evening sky. Mercury passed into superior solar conjunction on
October 27th. For three weeks following this conjunction, Mercury will be
too close to the Sun to be visible. VERDICT: Don’t bother to search
for Mercury until around Thanksgiving week, when it will high enough in the
west for viewing. It will return just before Thanksgiving week, but will
be exceedingly difficult to observe.
*VENUS: (Host constellation: Ophiuchus) PICK PLANET!*
As far as brightness is concerned Venus enjoys all the advantages. Its
pervasive clouds reflect about 67% of the sunlight it receives. It is
closer to the Sun than Earth, so the incidental sunlight is more intense.
It is also one of the closest planets to Earth, so the reflected light
isn't as diminished as it would be were it farther away. Also, Venus is
almost as large as Earth, so its reflective surface area is larger than the
other two terrestrial planets, Mars and Mercury. Venus is often the
pick planet because of these advantages. Venus remains a bright beacon
in the western evening sky throughout November. VERDICT: Easy to see
if one ventures outside soon after sunset. Venus is one of those celestial
bodies that appears during civil twilight. Seek it out in the early
evening western sky.
*MARS (Host constellation: Sagittarius)*
Careful observers will notice something rather peculiar about Mars. It
sets around the same time (9:30 p.m.) each night through November, just as
it did for most of October. This occurs because Earth and Mars are moving
relative to each other in such a way so that Mars' position relative to the
Earth-Sun line remains the same…at least for now. VERDICT: Even
though it is nearly 100 times dimmer than Venus, Mars is still a
conspicuous sight in the western evening sky. It will also remain visible
for about two hours after Venus sets.
*JUPITER (Host constellation: Virgo)*The second brightest planet, Jupiter
outshines all the night sky stars, but rises in the early morning eastern
sky. In fact, Jupiter is currently the only visible planet in the
morning sky. Jupiter rises a few minutes earlier each day and slowly
brightens throughout the year. VERDICT: If you're up before dawn,
treat yourself to some delectable eye candy. If you'd rather remain in
beautiful communion with your bed, you can wait to see Jupiter at more
decent hours later this winter.
*SATURN (Host constellation: Ophiuchus)*We lose Saturn just after mid
month. One might observe the sixth world low in the southwestern evening
sky during the first three weeks of November. Otherwise, it will be
lost to sight. Saturn passes through superior solar conjunction on December
10th and then will return to the pre-dawn eastern sky by late December.
VERDICT: Try to find Saturn before November 23rd. After that, wait until
the end of the year.
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FROM THE CATACOMBS OF INFINITE KNOWLEDGE
*"What IS that Julian date nonsense?"*
One difficulty astronomers encounter when specifying the precise timing of
an astronomical event is in choosing the proper calendar date and time.
The world is divided into many time zones and calendar systems are still
not uniform among all cultures. Our 10:55 a.m. November 13 is 7:55 a.m.
November 13 in California, but 1:55 a.m November 14 in Sydney, Australia.
What with all these different dates and times specifying the same
exact moment, astronomical bookkeeping can quickly become a bit dodgy.
Fortunately, astronomers use the Julian date system which assigns a unique
number to each moment. Devised in the 16th century by Joseph Justus
Scaliger, this system counts each day that has elapsed since January 1,
4713 B.C. Scaliger chose this date because it was the most recent year
which was a starting point for three three different cycles: the 19 year
lunar cycle, the 28 year solar cycle and a 15 year indiction cycle.
(Indiction cycles are civil inventions: time periods when, for instance,
land taxes were reassessed. The 15-year cycle chosen by Scalinger was the
one introduced by Roman Emperor Constantine. ) Scalinger was a
historian, not an astronomer and consequently developed his system for
historical purposes. Astronomers later adopted the system to precisely
pinpoint the time of astronomical events.
Noon on January 1, 4713 B.C . was specified as 0. The number increased
by one with every solar day that elapsed since this date. Look up at the
Julian date we listed in our heading today: 2457707.16
2,457,707 days have passed since January 1, 4713 B.C. Notice the
decimal. Another advantage of this system is that one can indicate a
precise time down to the second by using these decimals. We always use
the 0.16 as a rough estimation of the time around noon in the eastern time
zone for the given date. Of course, the Julian date changes rapidly and
continuously, so we could list the separate Julian date at the beginning of
each sentence. (Hmmm...maybe in the new year.)
*Joseph Justus Scaliger (1540-1609)**The French scholar who devised the
Julian date system astronomers still use to precisely indicate the time of
astronomical events. *
We can use this cycle for 7,980 years because 7,980 is the product of 15,
28 and 19, the duration of the indiction, solar and lunar cycles,
respectively. So, in about 1,250 years, we'll have to decide if we need
to begin anew, or not.
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