THE DAILY ASTRONOMER
Monday, December 12, 2016
Week 15 Night Sky Calendar
No, astronomical winter has not yet begun! We have more than week of astronomical autumn to enjoy before the scythe-wielding old man winter sows despair and discord amongst the populace. All the same, the winter constellations are rising into greater prominence and the evening sky is now adorned with myriad brilliant lights. Starting next week, we'll be featuring a new winter constellation at the beginning of these night sky calendars. This week, we'll focus on a faint, but famous, autumn pattern: Pisces the Fish.
Gaia, the Earth Goddess, and Uranos, the sky god, sired the Titans, including Cronos and Rhea, who, themselves, later sired the gods. Fearful of being usurped by his children as he, himself, had usurped Uranos, Cronos swallowed his children as they were born, save Zeus, whom Rhea secretly delivered in a Cretian cave. She presented Cronos with a blanket-swaddled rock, claiming it to be the infant Zeus, which Cronos promptly swallowed. Zeus and his mother then conspired to liberate the other gods by tricking Cronos to ingest an emetic that caused him to regurgitate the gods. The gods then successfully waged a 10 year battle against the titans who, when vanquished, were consigned to Tartarus, the punitive underworld region reserved for the most wicked.
Distressed at the fate of her children, Gaia seduced Tartarus and in so doing sired Typhon, a monster more formidable and horrific than any that ever appeared in the world before or since. (For instance, a hundred serpent heads protruded from one shoulder. These heads issued flame, bile and the worst noises the ear that hear, including the wailing of bereaved parents, shrieks of the tortured and screams of unbridled rage.) Gaia hoped that Typhon would destroy the gods and liberate the titans from Tartarus. Instead, the bestial and violent Typhon nearly destroyed the entire Universe and was only defeated after an epic battle lead by Zeus. During Typhon's reign of terror, love goddess Aphrodite and her son Eros transformed themselves into fish and retreated deep into a river. Not wanting to lose touch, they tied themselves to each other with a rope knotted in the middle. After Typhon's defeat, Aphrodite and Eros returned to the land and re assumed their human aspects. The constellation Pisces depicts Aphrodite and Eros in their piscine forms.
Pisces the Fish the form that Aphrodite and Eros assumed when hiding from the ferocious Typhon. Fearful of losing track of each other in the swift current, they were tethered to each other with two ropes knotted together. Image by Till Credner
Astronomically, Pisces is noteworthy as the Sun's host constellation on the vernal equinox. As Pisces draws closer to the setting Sun each day, we draw closer to Spring's inception. Tonight, Pisces the fish begins the night high in the western sky. The southern fish is just south of the Great Square of Pegasus and the northern fish is to the east of this square.
This week we experience a lunar occultation of Aldebaran, the unfavorable peak of the Geminid meteor shower, another super moon and the Sun enters Sagittarius, demonstrating that autumn's end is imminent.
MONDAY, DECEMBER 12: MOON 9.0 DEGREES SSW OF THE PLEAIDES
The moon is nearly full (97%) illuminated and will therefore appear quite bright. However, the Pleiades will be nine degrees to its south-southwest and will remain visible despite the bright moon's proximity. The moon will move through Taurus the bull and then will literally move in front of Taurus' brightest star, Aldebaran.
MONDAY, DECEMBER 12 AND TUESDAY, DECEMBER 13:
LUNAR OCCULTATION OF ALDEBARAN (PLATINUM EVENT!!!!)
Tonight, we will see Aldebaran, the brightest star in Taurus the Bull, appear to move behind the nearly full moon. This occultation is a "grazing" event because Aldebaran moves behind the upper part of the moon and then emerges soon after.
Lunar occultation of Aldebaran path. Observers within most of the continental United States will observe a "grazing lunar occultation of Aldebaran" tonight. Aldebaran will appear to move behind the moon's upper limb and then will emerge closer to its mid section. Image by Curt Renz
Such occulations have limited visibility. We are fortunate to be within the visibility region of this month's lunar occultation. The graphic above displays time ticks in Universal time. We subtract five hours to convert to Eastern Standard Time. The occultation will start before midnight. We recommend that observers venture outside around 11:20 p.m. in order to observe the entire sequence.
The occultation will occur around 11:22 p.m. Aldebaran will re emerge at 12:35 a.m.
Occultation begins Observers will observe Aldebaran disappear behind the moon along its upper limb. The star vanishes at 11:22 p.m. 12/12 and will reemerge at 12:35 a.m. 12/23. As the moon lacks an atmosphere, the star will disappear instantly as the moon passes in front of it. Image by John's Skynotes.
Technically, this event occurs on Monday night into Tuesday morning! For this reason, we listed both dates at the heading of this passage.
WEDNESDAY, DECEMBER 14: FULL MOON (SUPER MOON!) GOLD EVENT!!!
The moon will be full tonight and was at perigee on December 12th. As today's weekly sky calendar is turning out to be quite heavy, we'll wait until tomorrow to discuss the super moon in greater detail.
WEDNESDAY, DECEMBER 14; GEMINID METEOR SHOWERS PEAKS
The full moon is beloved by most, but detested by meteor watchers as the lunar light interference washes out all but the brightest meteors. The Geminid meteor shower peaks occurs during this particularly brilliant full moon, so 2016 is not a favorable year for the Geminids.
Generally, 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. Ordinarily, one can expect to see 20 - 35 meteors an hour. This year, one will be lucky to see 5 - 10 due to the lunar light glow.
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.
SATURDAY, DECEMBER 17: MOON 4.7 DEGREES SOUTH OF BEEHIVE CLUSTER
The waning gibbous moon will be 82% illuminated tonight. We will see it south of Praesepe, also known as the "Beehive Star Cluster," a prominent feature within Cancer the Crab. See them both rising in the mid evening and will be high in the eastern sky by midnight.
SUNDAY, DECEMBER 18: 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, 2017.
PLANET WATCH:
MERCURY (Host constellations: Sagittarius-Ophiuchus)
The first world peeks up in the western evening sky. This apparition favors southern observers, but Mercury remains visible low in the southwest for northern sky watchers. Mercury will be at greatest eastern elongation on December 11th, but at inferior conjunction on December 28th. Mercury will vanish around the third week of December. VERDICT: We would advise you to venture out during the first half of December to find Mercury. The elusive world vanishes late this month.
VENUS (Host constellation: Sagittarius) PICK PLANET!
People wonder why Venus is such a prima donna when she receives the coveted "pick planet' diadem almost every month. Venus enjoys the advantage of being the brightest planet, so whenever it appears it will invariably outshine it planetary cohorts. This month Venus shines brilliantly as the western evening sky star. VERDICT: Easy to find if you're outside in the early evening. Look west and just behold the spectacle.
MARS (Host constellation: Capricornus - Aquarius)
Here's an interesting observational exercise: observe Mars in the western evening sky throughout December. One will notice that Mars is setting around the same time each night. Mars has been setting around 9:30 p.m. each night this autumn because Earth and the red planet are moving in such a way as to make their positions relative to each other nearly constant. VERDICT: Not only can you see the red planet, you can almost set your watch by it. What's not to love?
JUPITER (Host constellation: Virgo)
Rising earlier each morning, Jupiter is the only pre-dawn planet visible to the naked eye. The fifth sphere serves as a the brilliant eastern beacon one can easily see provided one ventures outside a couple of hours before sunrise. VERDICT: The perfect planet for joggers, dog walkers, and those accursed few who always arise with alacrity before the alarm blares,
SATURN (Host constellation : Ophiuchus)
We're sorry to say that we have to bid Saturn adieu, at least for awhile. The ringed world vanishes into the dusk, destined to return to the pre-dawn sky by late December. Saturn is in solar conjunction on December 11th. VERDICT: Don't bother to seek out Saturn until just before the New Year's celebrations.
© 2016 Edward Gleason