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. 

________________________________________________________

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.      

_________________________________________________________________________________