Friday, December 24
Christmas star: Sirius, the
brightest star in the night sky, rises in the southeast around 7 or 8
p.m. (depending on where you live in your time zone). Orion's Belt
points down nearly to Sirius's rising point, showing where to watch for
it. When Sirius is low it often twinkles in vivid, flashing colors, an
effect that binoculars reveal especially clearly. All stars do this, but
only Sirius is bright enough to do it so visibly.
Saturday, December 25
Merry Sol Invictus!
In the late Roman Empire December 25th was the Birthday of the
Unconquered Sun — marking the Sun's survival past its seasonal dark
decline with the promise of a new spring and summer to come. Along with
other solstice-period celebrations (including the birthday parties of
numerous pagan deities), the date and the symbolism were taken over by
Christianity and officially set to be Christmas in the 4th century.
Carefully note the sunset point on your horizon from day to day. Can you
see that it's already beginning to creep a little north?
Christmas also marks the time of year when iconic Orion finally clears
the east-southeast horizon and sparkles in full view soon after twilight
ends (for skywatchers at mid-northern latitudes).
The
eclipsing variable star Algol is at its minimum light, magnitude 3.4
instead of its usual 2.1, for a couple hours centered on 1:08 a.m.
Sunday morning Eastern Standard Time (10:08 p.m. Christmas evening
Pacific Standard Time).
Jupiter's Red Spot crosses Jupiter's central meridian around 11:04 p.m. EST; 8:04 p.m. PST.
Sunday, December 26
Two famous "enclosure"
asterisms lie upper right of Jupiter these evenings: the small, dim
Circlet of Pisces, and, farther on, the big, brighter Great Square of
Pegasus. Also, far below Jupiter in early evening, look for Fomalhaut.
The tiny black shadow of Jupiter's moon Europa starts crossing the
planet at 8:06 p.m. EST. Just five minutes later, Europa itself leaves the opposite limb of Jupiter. Europa's shadow leaves Jupiter's face at 10:46 p.m. EST.
Stick your head out around 3 a.m., and the waning Moon guides your way to Saturn.
Monday, December 27
Last-quarter Moon tonight
(exact at 11:18 p.m. EST). The last-quarter Moon always rises around the
middle of the night, in a constellation that won't appear high in the
evening sky until one season ahead. In tonight's case the Moon is in
Virgo, a constellation best known in spring. Look for Saturn to the
Moon's left, as shown here (on the morning of the 28th).
Tuesday, December 28
Dawn and sunrise are
now happening nearly as late by the clock as they're going to. Look
southeast in early dawn Wednesday morning for the Moon, Saturn and
Spica. For North America, Spica is just a few degrees from the Moon —
upper left of the Moon at 3 a.m. as shown here, and above the Moon by
dawn. Saturn at dawn is off to their upper right. Venus, much brighter,
shines far to the Moon's lower left.
Jupiter's Red Spot crosses Jupiter's central meridian around 8:35 p.m. EST this evening.
The
eclipsing variable star Algol is at its minimum light, magnitude 3.4
instead of its usual 2.1, for a couple hours centered on 9:58 p.m. EST
this evening.
Wednesday, December 29
A small telescope,
or steadily held binoculars, will show the 5.5-magnitude star 20 Piscium
just 4 arcminutes (six Jupiter diameters) to Jupiter's south or
southeast, looking like a very out-of-place Galilean moon. With a
slightly larger telescope, here's a chance to compare Jupiter's moons at
high magnification with a star. In good seeing, their non-stellar
nature is fairly plain.
And don't miss Uranus, magnitude 5.8, currently 50 arcminutes to
Jupiter's north-northeast. It looks even more un-starlike at high power.
During dawn Thursday morning, spot the waning
crescent Moon with Venus to its left. Can you follow Venus with your
unaided eyes right through sunrise?
Thursday, December 30
Jupiter's Red Spot crosses Jupiter's central meridian around 10:14 p.m. EST; 7:14 p.m. PST.
As the Moon wanes further, it points the way to Venus, Antares, and newly arrived Mercury.
At dawn Friday morning, Venus shines upper left of the Moon.
Friday, December 31
The eclipsing variable
star Algol is at its minimum light, magnitude 3.4 instead of its usual
2.1, for a couple hours centered on 6:47 p.m. EST.
After the noise and revelry at the turning of midnight, step outside
into the silent, cold dark. If the sky is clear, Sirius will be shining
at its highest in the south. To its upper right, Orion is just beginning
to tilt westward. To Sirius's upper left shines Procyon. And (if you're
near latitude 39° north) Capella and the Castor-Pollux pair straddle
the zenith. This is a preview of how the constellations will look at
dusk at winter's end.
At dawn on the morning of
January 1st (are you really going to be up then?) look far below Venus
in the southeast for the thin crescent Moon. Antares and Mercury are
also in the scene, as shown at right.
Saturday, January 1
Sirius, the Dog Star,
sparkles low in the east-southeast after dinnertime. Procyon, the Little
Dog Star, shines in the east about two fist-widths at arm's length to
Sirius's left. If you live around latitude 30° (Tijuana, New Orleans,
Jacksonville), the two canine stars will be at the same height above
your horizon soon after they rise. If you're north of that latitude,
Procyon will be higher. If you're south of there, Sirius will be the
higher one.
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