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Star Gazing - December 17, 2018
Monday, December 17
• The Summer Triangle is sinking lower in the west after dusk, and Altair is the first of its stars to go (for
mid-northern observers). Start by spotting bright, zero-magnitude Vega in the northwest right after dark.
The brightest star above Vega is Deneb. Altair, the Triangle's third star, is farther to Vega's left or lower
left. How late into the evening, and into the advancing season, can you keep Altair in view?
Tuesday, December 18
• For the next few days the asteroid 6 Hebe, magnitude 8.6, is passing just south of the dim Rosette Nebula
in Monoceros with its central star group NGC 2244. They're high in late evening. See the article and finder
chart in the December Sky & Telescope, page 50.
Moon, Pleiades, Aldebaran: Dec. 19-21, 2018
Every December, the Moon is nearly full when it crosses Taurus in the eastern evening sky.
Wednesday, December 19
• The waxing gibbous Moon shines in the east this evening, with the Pleiades to its left and orange Aldebaran
to its lower left.
To the right of the Moon is orange Alpha Ceti, fainter at magnitude 2.5.
At this fulsome phase the Moon displays all of sinuous Mare Frigoris, north of big round Mare Imbrium.
Explore along its length with your telescope and Chuck Wood's Exploring the Moon article, "Imbrium's
Eyebrow," in the December Sky & Telescope, page 52.
Thursday, December 20
• Now the Moon shines in the Hyades, near Aldebaran and below the Pleiades, as shown here.
• Venus will occult a 6th-magnitude star before or during dawn tomorrow morning the 21st for much of
central and eastern North America. Venus will be a thick crescent, 41% sunlit; the star is about 10,000 times
fainter. "Only the dark-side reappearance can be seen, but it can be observed well, with any telescope with
high power, since the dazzling sunlit parts of Venus will be at least 15 arcseconds away," writes David
Dunham of the International Occultation Timing Association. Amateurs with large scopes who can do rapid
imaging or video recording may be able to document brightenings and fadings of the star as its light is
refracted by layers of Venus's atmosphere. You might even record the brief, globe-encircling central flash
exactly at mid-occultation on the centerline.
But if you're too far east the sky will be too bright, and too far west Venus will be too low. Maps, local
timetables, and observing details and tips.
• You are remembered, Carl Sagan (November 9, 1934 – December 20, 1996).
Friday, December 21
• The Moon, nearly full this evening, forms an almost-isosceles triangle with Aldebaran to its upper right
and Betelgeuse to its lower right. Aldebaran is an orange, K5 giant star 65 light-years away. Betelgeuse is
an orange, slightly less hot M1 supergiant about 10 times more distant.
Saturday, December 22
• Full Moon (exact at 12:49 p.m. EST). The Moon, near perigee, is between the feet of the Castor figure
and the dim Club of Orion. Farther to the left or lower left of the Moon are brighter Castor and Pollux.
Farther right or lower right of the Moon is Orion, with his belt almost vertical.
The full Moon of December rides higher across the sky in the middle of the night than it does in any other
month (for Northern Hemisphere skywatchers), "giving luster of midday to objects below."
• Algol should be at minimum brightness for a couple of hours centered on 11:36 p.m. EST. Algol takes several
additional hours to fade and to rebrighten.
Starry, Starry Night . . .
"I know nothing of any certainty, but the sight of the stars
makes me dream." -Vincent Van Gogh