Friday, December 20
Now that the evening sky is Moon-free, it’s time to aim for fainter targets, including 12th-magnitude Comet 333P/LINEAR. Located in far northern Cygnus, close to where that constellation’s border meets those of Cepheus and Draco, LINEAR sits some 8.4° northeast of magnitude 3.8 Kappa (κ) Cygni tonight. The comet is roughly halfway along a line drawn between a 4th-magnitude and 5th-magnitude field star, oriented southeast-northwest.
Continue your gaze an additional 4.2° northeast of the comet, and you’ll land on 8th-magnitude NGC 6939, an open cluster in Cepheus. Just to the cluster’s southeast is the spiral galaxy NGC 6946, about a magnitude fainter but roughly the same size, some 10’ on the sky.
It’s best to search these targets out early in the evening, as soon as the sky grows dark. Two hours after sunset, LINEAR is still 40° high in the northwest, but will sink lower as the hours pass and Cygnus swoops toward the horizon.
Sunrise: 7:18 A.M.
Sunset: 4:38 P.M.
Moonrise: 10:19 P.M.
Moonset: 11:11 A.M.
Moon Phase: Waning gibbous (70%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.
Saturday, December 21
The winter solstice occurs at 4:21 A.M. EST. This moment marks the time when the Sun appears farthest south in the Northern Hemisphere sky, resulting in the shortest day and longest night of the year for this part of the world. After today, daylight in the Northern Hemisphere will slowly begin increasing.
The winter solstice also officially rings in its eponymous season — winter has officially begun for those who live north of the equator.
About an hour before sunrise this morning, turn your gaze toward the southeastern horizon to look for two bright points of light low in the sky. The higher and brighter of the two is magnitude –0.2 Mercury; to its lower right is fainter magnitude 1.2 Antares. The latter is a red giant star that marks the heart of the constellation Scorpius. Its ruddy color causes some observers to mistake it for the planet Mars.
The two will rise together as dawn begins to brighten the sky. Antares will be lost to the growing morning light first. How long after that does Mercury remain visible?
Mercury will pass 7° due north of Antares later today at 7 P.M. EST, when both are below the horizon.
Sunrise: 7:19 A.M.
Sunset: 4:38 P.M.
Moonrise: 11:20 P.M.
Moonset: 11:33 A.M.
Moon Phase: Waning gibbous (61%)
Sunday, December 22
The Geminids may have had poor prospects this year, but the Ursid meteor shower peaks this morning with less interference from Earth’s satellite, as the Moon has both dimmed and now sits at the opposite end of the sky as the shower radiant.
That radiant— the point from which meteors appear to originate — lies just northwest of Kochab, Ursa Minor’s beta star and the southwesternmost point in the Little Dipper’s cup. At magnitude 2.1, it’s also the brightest star in the Little Dipper asterism. Once you’ve located the Little Dipper in the north, look some 40° to 60° away from its cup, to either side. These regions are where the streaks of light left by shower meteors will be the longest.
The Ursids have a relatively low maximum zenithal hourly rate of 10 meteors per hour but can be quite variable, sometimes generating up to 50 meters per hour. Plus, the radiant lies so far north that it’s visible all night, so you can watch for shooting stars whether you’re up late or early! However, the radiant will be highest in the early morning, and this is also when meteor rates are likely to be at their best, so if you’re willing to get up early, you may be richly rewarded.
Last Quarter Moon occurs this afternoon at 5:18 P.M. EST.
Sunrise: 7:19 A.M.
Sunset: 4:39 P.M.
Moonrise: —
Moonset: 11:52 A.M.
Moon Phase: Waning gibbous (52%)
Monday, December 23
Jupiter is still blazing bright, some two weeks after it reached opposition earlier this month. It remains at its brightest for a few more days, shining at magnitude –2.8 in the constellation Taurus. The gas giant sits just over 6° from the Bull’s alpha star, Aldebaran, appearing to the upper left of the star as the constellation rises in the evening sky. The planet appears to stand almost directly above Betelgeuse, the bright star marking Orion the Hunter’s lower shoulder as he rises following Taurus.
Jupiter’s disk is a magnificent 48” wide, showing off alternating light and dark cloud belts through a telescope. Later in the evening, the Great Red Spot — a long-lived, hurricane-like storm in the planet’s southern hemisphere — appears, rotating into the middle of the disk around midnight Eastern time.
Earlier in the evening, the planet’s icy moon Europa transits the disk, followed by its shadow projected onto the cloud tops. The moon and shadow are already crossing the disk from east to west as night falls and Jupiter rises in the Eastern time zone; the pair straddle the central meridian, with Europa west of the planet’s center and its shadow to the east, around 5:40 P.M. EST, and Europa leaves the southwestern limb shortly before 6:30 P.M. EST. Its shadow slips away some 45 minutes later, around 7:15 P.M. EST.
Keep watching, and you’ll see Europa pull away to the west even as Io closes in from that side (Ganymede and Callisto lie even farther west, with the former closer to the planet). Io disappears behind the planet in an occultation around 11:45 P.M. EST, reappearing around 2:20 A.M. EST (now the 24th in all time zones except Pacific) after also crossing through the planet’s shadow, which stretches behind it to the northeast.
Sunrise: 7:20 A.M.
Sunset: 4:39 P.M.
Moonrise: 12:19 A.M.
Moonset: 12:11 P.M.
Moon Phase: Waning crescent (42%)
Tuesday, December 24
The Moon reaches apogee, the farthest point from Earth in its orbit, at 2:25 A.M. EST. At that time, our satellite will stand 251,335 miles (404,484 kilometers) away.
Look south an hour before sunrise and you’ll see the waning crescent Moon just to the upper right of a bright, 1st-magnitude star. This is Spica, Virgo’s alpha star. You may even spot earthshine illuminating the portion of the Moon now in shadow, caused by sunlight bouncing off Earth. It’s a beautiful scene.
The Moon passes 0.2° north of Spica at 3 P.M. EST. By the time Virgo rises again — shortly before 2 A.M. local time tomorrow morning — the Moon will have moved on, now more than 7° southeast of Spica.
Mercury is at greatest western elongation at 10 P.M. EST, reaching a point 22° from the Sun. It, too, is in the early-morning sky, shining at magnitude –0.3 in the constellation Ophiuchus. The solar system’s smallest planet sits to the upper left of the bright red giant star Antares in Scorpius, rising roughly 90 minutes before the Sun. Through a telescope, Mercury is now just over 60 percent lit — an increase of over 10 percent from last Friday, when it was 50 percent illuminated.
Sunrise: 7:20 A.M.
Sunset: 4:40 P.M.
Moonrise: 1:19 A.M.
Moonset: 12:31 P.M.
Moon Phase: Waning crescent (33%)
Wednesday, December 25
For those who celebrate Christmas, there’s a festive set of lights rising in the east not long after sunset tonight. Fourth-magnitude NGC 2264, also called the Christmas Tree Cluster, is one of the brighter open star clusters in the wintertime sky.
Located in Monoceros the Unicorn, you can find NGC 2264 to the lower left of Betelgeuse, Orion the Hunter’s bright shoulder, in the early-evening hours tonight. The easiest way to find it is to first locate Xi (ξ) Geminorum, a magnitude 3.4 star that lies at the feet of Gemini the Twins, in the far southern reaches of that constellation. NGC 2264 is a short 3° hop south-southwest from that star.
The brightest star in the cluster, 15 Monocerotis, is at the base of the Christmas Tree’s trunk, while a wedge-shaped pattern of stars pointing away from it forms the festive tree itself. Note that depending on your optics, the tree may appear sideways or even upside-down, so take your time looking for the pattern. The entire cluster spans about a degree, so it’s rather large. Reaching “down” toward the top of the tree is the Cone Nebula, whose tip is alight with young, forming stars, while its base is composed of dark dust that blocks out the background stars.
Sunrise: 7:21 A.M.
Sunset: 4:40 P.M.
Moonrise: 2:19 A.M.
Moonset: 12:53 P.M.
Moon Phase: Waning crescent (25%)
Thursday, December 26
Saturn’s rings are slowly thinning as the tilt of the planet relative to our line of sight shrinks. Tonight, that angle is 4.4°, but by the end of the first week of January, it will dip below 4°. The trend will continue as Saturn nears conjunction with the Sun, which it reaches March 12, less than two weeks before the viewing angle of the rings drops to 0 as Earth crosses the plane of the rings and they thin to invisibility. Unfortunately, on that date — March 23 — Saturn will be less than 10° from the Sun, unable to be viewed from Earth. But for now, we can watch the strange progression as the rings grow ever thinner over the next few months; consider documenting the planet’s appearance every few weeks with a quick sketch or astrophoto.
Saturn still hangs in Aquarius, visible for about six hours after sunset. The ringed planet glows at magnitude 1, still the brightest point of light high in the southern sky, though to its lower right, about 25° above the horizon an hour after sunset, is unmissable Venus (magnitude –4.4). To Saturn’s lower left, forming the third point in a large triangle in this part of the sky, is magnitude 1.2 Fomalhaut, the alpha star of Piscis Austrinus.
Telescopic views of Saturn show the planet’s 17”-wide disk as well as those thin rings, which stretch some 38” end to end, with a minor axis spanning just 3”. The planet’s brightest moon, Titan, lies far to the west of the ringed world tonight, while fainter, 10th-magnitude Rhea, Tethys, and Dione are close by. Rhea lies west of the planet and Tethys to the east. Dione sits just off Saturn’s southeastern limb early in the evening, transiting the disk starting just before 8 P.M. EST. The transit lasts nearly three hours, with Dione slipping off the disk shortly before 9:45 P.M. CST, when Saturn is low in the Midwest and has already set for observers on the East Coast.
Those on the West Coast might be able to catch the very start of Tethys’ transit, which also begins at the planet’s southeastern limb shortly after 9 P.M. PST. However, note that both Dione and Tethys’ transits will be hard to follow visually, and are best captured with astrophotography — particularly high-speed video.
Sunrise: 7:21 A.M.
Sunset: 4:41 P.M.
Moonrise: 3:22 A.M.
Moonset: 1:19 P.M.
Moon Phase: Waning crescent (17%)
Friday, December 27
The dark feature Mare Cimmerium lies roughly central on the martian disk at local midnight in the central U.S. this evening. Magnitude –1.2 Mars is in Cancer; the planet rises around 6:30 P.M. local time and remains visible until sunrise. By midnight, the planet stands 60° high in the east, to the upper right of the Sickle of Leo and the upper left of bright Procyon in Canis Minor. Just below Mars is the Beehive Cluster, also cataloged as M44. With no Moon in the sky, you may be able to spot this object with the naked eye, either as a dim, fuzzy glow or perhaps as a few scattered points of light. Binoculars or a low-powered scope will reveal many more of the bright cluster’s stars.
Moving on to Mars, turn the largest scope you have on the planet’s ruddy disk, which now appears 14” wide and 98 percent lit. As the planet rotates, features appear at the eastern limb and move west. As Mare Cimmerium moves away from the center of the disk after local midnight in the mid-U.S., the larger, even darker Syrtis Major appears in the east, with the brighter Hellas region to its south. High-speed video capture is the best way to pick up details on the planet’s surface, though if you have a clear, dark sky, you may be able to visually spot lighter or darker areas on the small disk, particularly during random moments of excellent seeing.
Sunrise: 7:21 A.M.
Sunset: 4:42 P.M.
Moonrise: 4:26 A.M.
Moonset: 1:50 P.M.
Moon Phase: Waning crescent (10%)
Sky This Week is brought to you in part by Celestron.