The Night Sky Tonight: December 11 – December 24

By Mark Wagner

Friday, December 11

6 Trianguli is an easy to find colored binary double stars just east of the three bright stars comprising Triangulum?s constellation figure. At a distance of 294 light years, the combined magnitude of 4.93 make is easily visible unaided in dark skies, or in a magnifying finder from in town locations. The yellow primary is magnitude 5.26 and blue companion one and a half magnitudes dimmer at P.A. 69, separated by a close 3.7 arc-seconds. You should notice the pair splitting in low power views, but the colors will be prominent with higher power.

Skill Level: Beginner

Tomorrow Lunar Occultation Of Venus.

Saturday, December 12

Late this morning, Pacific Standard Time, observers in the western United States will be treated to a daytime occultation of Venus by our Moon. Have you even seen Venus in bright daylight? It is surprisingly easy to do knowing its approximate distance from the Sun. Today the 4% waning crescent Moon will pass in front of Venus, an interesting sight in a telescope or binoculars. The image at left is with a darkened sky to show the Moon approaching Venus. Find the timing information here: https://in-the-sky.org/news.php?id=20201212_16_100

Skill Level: Beginner

Tomorrow Evening: Geminid Meteor Shower.

Sunday, December 13

The Geminids is one of the great meteor showers of the year, and with an only 1% Moon tonight, this is a prime date. These are often bright and intensely colored with medium-slow velocity. Look toward Gemini just east of Orion?s great red star Betelgeuse to the shower?s radiant, from where the shooters will appear to come from. The shower is from debris left in the trail of asteroid 3200 Phaeton. Find a dark place, dress warm, have a warm drink and bring a comfortable seat for this show!

Skill Level: Beginner

Tomorrow Morning: Total Solar Eclipse.

Monday, December 14

If you are lucky enough to be in South America, you may have an opportunity to witness today?s total solar eclipse. The center line, where the entire disk of the Sun will be covered, crosses southern Chile and Argentina. Lesser degrees of eclipse will be visible over much of the continent. How many of you have experienced this wonder in person? What were your impressions?

Skill Level: Beginner

Suggested Gear: Orion Scenix 10x50 Binocular Solar Kit

Tomorrow Morning: Constellation Bootes

Tuesday, December 15

Bootes is a great summer constellation, anchored by its magnitude -0.07 (A) red giant Alpha star Arcturus, 36 light years from us and the 4th brightest star in northern skies. With 907 square degrees Bootes is the 13th largest constellation in area, and is ancient, dating to Babylon with entries in Homer?s Odyssey. Home to dim galaxies and globular clusters, it also contains some outstanding double stars. Neighboring constellations include (1) Canes Venatici, (2) Ursa Major, (3) Draco, (4) Hercules, (5) Corona Borealis, (6) Serpens, (7) Virgo and (8) Coma Berenices.

Skill Level: Beginner

Tomorrow Evening: Planetary Triplet.

Wednesday, December 16

An hour after sunset this evening you can treat yourself and others to the outstanding sight of Saturn and Jupiter in conjunction over our thin crescent Moon. The Moon is 2.4 days old with 7.3% illumination and 373,000 km from us. Jupiter sits 4-1/4 degrees above the Moon and almost 5.9 astronomical units (AU) away (5.9 times the Earth?s 93 million miles distance from the Sun) shining at a bright magnitude -1.98. Only half a degree above Jupiter Saturn sits nearly 10 AU from us glowing warmly at magnitude 0.63. They may all fit in one binocular field of view.

Skill Level: Beginner

Tomorrow Morning: Double Star Epsilon Bootes

Thursday, December 17

Epsilon Bootis is a fine challenge double star located conveniently along the constellation figure of Bootes 203 light years distant. At magnitude 2.34 it is obvious even in brighter skies. An orange magnitude 2.58 primary coupled with its excellent magnitude 4.81 secondary and separated by a tight 2.8 arc-seconds is a favorite among double star observers. Known as Izar (Arabic for veil) it was named Pulcherrima, meaning ?the loveliest?, by Friedrich Georg Wilhelm von Struve, great grandfather of famous double star observer Otto Struve.

Skill Level: Beginner

Tomorrow Evening: Moon Targets.

Friday, December 18

Tonight?s waxing crescent Moon is 4.4 days old at 22.6% illumination. West of Mare Crisium in 10X binoculars find (1) Palus Somni, a 120x60 area of ridges and flat unusual terrain of usual coloration. (2) Crater Macrobius to the northwest is good with 50mm instruments, 39 miles in diameter with very high walls, terraces, a flat floor and central mountain. Locate (3) Crater Hill then to its north (4) Macrobius X in 200mm instruments, isolated with its bowl shaped rounded floor. Using 300mm try for (5) Romer J1, an extrusive volcanic shield of 1.2 miles diameter.

Skill Level: Beginner

Tomorrow Morning: Globular Cluster Challenge NGC 5466.

Saturday, December 19

Are you ready for a challenge target this morning? NGC 5466 is large at 11 arc-minutes but dim magnitude 9.1 globular, a distant 52,000 light years from us. Find it hopping from (A) Arcturus to (1) 12 Bootis and (2) 9 Bootis, both at or under magnitude 5.0. The inset detail shows its location. This cluster is part of a recently discovered stream of such objects that form a discrete band around our galaxy. Discovered by Sir William Herschel in 1784, its low surface brightness make is a target for darker skies.

Skill Level: Intermediate

Suggested Gear:

Tomorrow Evening: Jupiter And Saturn Conjunction.

Sunday, December 20

Here?s a sight that hasn?t been visible for 397 years. Jupiter and Saturn are in conjunction, just under eight arc-minutes apart in apparent distance. Jupiter is at 5.92 A.U. from earth, Saturn 10.8 A.U. from us. Jupiter is the normally third and sometime fourth brightest object in our sky at magnitude -1.97, Saturn significantly dimmer at 0.63. Estimate their combined magnitude and compare it to tomorrow morning?s Venus (at -3.94) over the eastern horizon. Telescope views will show both planets and moons in one field of view, an extremely rare treat!

Skill Level: Beginner

Tomorrow Morning: End Of Year Solstice.

Monday, December 21

Is it the beginning of Summer, or Winter? Depends on where you live, of course. Northern hemisphere residents celebrate Winter Solstice, Southern humans Summer Solstice. One hemisphere is tilted toward the Sun to it maximum 23.5 degrees, the other away as much as possible. Days begin growing longer in the north, and shorter in the south. Which do you celebrate?

Skill Level: Beginner

Suggested Gear: , Orion Resolux 7x50 Waterproof Astronomy Binoculars

Tomorrow Evening: Ursid Meteor Shower.

Tuesday, December 22

The Ursid Meteor Shower reaches its peak of activity tonight, a Christmas present for observers. The usual rate is much lower than the recent Geminid shower, but you can expect to pick up 5-10 per hour, although there are rate outbursts of over 25 per hour. Wait until after moon set for the best chance of seeing activity. The shower is medium speed averaging 20 miles per second, and appears related to Comet 8P/Tuttle.

Skill Level: Beginner

Tomorrow Evening: Moon Targets.

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Wednesday, December 23

Tonight?s 9.4 day old Moon is paired nicely tonight with Mars, at 69.5% illumination and near apogee. Both (1) Plato and (2) Clavius, north and south, are fine 10X binocular targets tonight. With a 50mm instrument (3) Copernicus will be outstanding. Nearby is (4) Stadius T, a wonderful chain of craterlets running north-south for 100mm views. In 300mm (5) Rima Birt is paired with an anonymous parallel groove.

Skill Level: Beginner

Suggested Gear:

Tomorrow Morning: Colored double Xi Bootis.

Thursday, December 24

Are your skies clear this Christmas Eve morning? Take your telescope out to check out the beautiful colored double star Xi Bootes. This binary star system is very close by at just under 22 light years, shining at a combined magnitude 4.53. Can you see it without a magnifying finder in your skies? If not, it is easy in a finder. The primary is magnitude 4.76 and companion 6.95 with 5.3? separation at PA 298. When you observe it, tell us the colors.

Skill Level: Beginner

Tomorrow Evening: More Moon Targets.

Charts from Starry Night Pro. 6 Trianguli, Izar and Xi Bootis sketches from Jeremy Perez. Solar Eclipse path and Solstice images from NASA. Lunar images courtesy NASA LRO.

Mark Wagner is a lifelong astronomy enthusiast and deep sky observer in the San Francisco bay area. Visit our Facebook Page if you'd like to post comments, questions, sketches or images you've taken to our Night Sky Tonight post.