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:  2457714.16

            "The one turkey that won't be cooked."

THE DAILY ASTRONOMER

Monday, November 21, 2016

Week 12 Night Sky Calendar

Scorpius the Scorpion is often called the "Thanksgiving Constellation," because the Sun appears to pass through it during Thanksgiving.     We know that Thanksgiving, being the fourth Thursday of November,  can be as early as November 22nd or as late as November 28th.    The Sun generally enters the Scorpius region around November 22nd and then departs on or just after November 29th.   Therefore, if you are settling down for Turkey day with your nearest, dearest and far too nearest, know that as you're coveting the moist drumstick, but avoiding all five metric tons of the fruitcake,  the fearsome scorpion lurks behind the Sun, destined to return to the early morning winter sky.

Gobble! Gobble!    Scorpius the Scorpion is known

as the Thanksgiving constellation because the Sun appears

to move through it during this high caloric holiday.

This week brings us the last quarter moon,  a nearly hidden Mercury-Saturn appulse, a close lunar encounter with Jupiter, and the moon at apogee.  (Since we devoted so much time to the perigee, we should at least give passion mention to its polar opposite.)     While this week might not prove as hyper-kinetic as last week, the sky remains as exquisitely interesting and indefatigably active as ever.    Welcome to week 12 of 1,989,110,334,115!

MONDAY, NOVEMBER 21:  LAST QUARTER MOON

Last Quarter Moon

First, the last quarter moon rises around midnight.   However, this time is only an approximation.  The last quarter moon tends to rise earlier than midnight around the autumnal equinox, but later than midnight around the spring equinox.    Around the solstices, the last quarter moon rises close to midnight.     

Second, the last quarter moon is slightly dimmer than the first quarter moon, as the illuminated region we observe at last quarter contains more darker areas (maria) than that visible during the first quarter moon.

TUESDAY, NOVEMBER 22:  SUN ENTERS SCORPIUS

Yes, the Sun' moves into the Scorpius region today.  We won't see anything, of course, as the Sun will block out the scorpion's stars. The Sun appears to move into the sky region Scorpius occupies because Earth has moved to the far side of the Sun relative to these stars. The Sun appears to move through thirteen constellations each year. These constellations are SCORPIUS THE SCORPION, Ophiuchus the Serpent Charmer, 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, and Libra the Scales. The Sun spends less time in Scorpius than in any other single constellation. The Sun appears to move into Ophiuchus on Tuesday,  November 29. 

WEDNESDAY, NOVEMBER 23:  MERCURY 3.4 DEGREES SOUTH OF SATURN

This one is essentially an academic event, as both planets will be only 15 degrees from the Sun in the western evening sky.  The closest naked-eye planet to the Sun appears to pass just south of the most distant naked eye planet.   Mercury, at magnitude -0.5, will appear 2.5 times brighter than Saturn, magnitude 0.5.    Of course, Mercury has the advantage of proximity, as it will be about 892 million miles closer to Earth than Saturn.

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

Messier 71: The Globular in Disguise

M71:  The "loose" globular cluster located in the

Sagitta constellation.     For two centuries

astronomers wondered if it was an open cluster, like the Pleiades

or a much larger globular cluster, such as Omega Centauri. 
Astronomers now know M71 is a globular cluster, albeit a loosely

bound and comparatively small one.    Image: NASA/HST
​

​As our Messier tour continues, we will encounter objects that are not nearly as prominent as the Orion Nebula (M44) or the Andromeda Galaxy (M31).   Today's stop takes us to a particularly strange globular cluster designated as M71.   As is true with many Messier objects, this one was not discovered by Charles Messier.     It was first observed in 1746  by French astronomer Philippe Loys de Chéseaux whose instrument was incapable of revealing its stellar components.     Charles Messier first observed it in 1780 and also classified it as a "nebula with no stars."    Three years later prolific astronomer William Herschel first resolved this object into stars.   As it seemed so loosely bound, this cluster was not immediately recognized as a "globular."  In fact, astronomers debated the character of this cluster until the 1970's,, when they finally classified M71 as a globular cluster, as opposed to an open or  galactic cluster.

This globular cluster is 12,000 light years from Earth and has a diameter stretching 27 light years.    Even with a pair of good binoculars, one can observe this cluster within the Sagitta constellation.      Search for it between the constellation's  gamma and delta star:

Look for M71 in the constellation Sagitta.

(Sagitta is tucked inside the Summer Triangle.)

One can observe this globular cluster with binoculars,

but a telescope is necessary if one wishes to resolve its stars.

One will need a telescope to observe some of its stars, however.    While admiring this beautiful, but loose, cluster, realize that you're observing a globular cluster that is between 9 - 10 billion years old, young by globular standards.       ​   Even seasoned sky watchers might perceive it as a rich galactic instead of a loosely bound globular.  However, in astronomy, as in life, not everything is as it seems.

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