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Last updateWed, 27 Sep 2017 1pm

Evenings during twilight in early December 2017 feature a half-dozen stars of first magnitude or brighter, including the Summer Triangle of Vega, Altair and Deneb well up in the west, getting lower as month progresses; Fomalhaut, mouth of the Southern Fish, in the south; and Capella, the Mother Goat star, ascending in the northeast, with red-orange Aldebaran, eye of Taurus, to its lower right.

Binoculars and an unobstructed view are needed to spot Saturn, with Mercury close to its lower left, very low in the southwestern twilight glow 2.8 to 2.3 degrees apart Dec. 1-3, some 40 minutes after sunset. But both sink lower each evening, with Mercury fading to the equal of Saturn by Dec. 3, and fading rapidly thereafter. Mercury passes inferior conjunction, nearly between Earth and the sun, on Dec. 12, and Saturn hides in conjunction on the far side of the sun on Dec. 21.

In evening twilight late in month—or later in the evening in early December—watch the eastern horizon for the rising of reddish Betelgeuse and blue-white Rigel. About midway between them, Orion’s vertical three-star belt confirms their identity as Hunter’s shoulder and foot.

Our morning chart (below) depicts the sky about 45 minutes before sunrise, but we advise you to begin viewing at least a half-hour earlier than that, to allow time to locate all the bright objects before they are drowned out in the brightening twilight. Steady Jupiter in the southeast is the most prominent object during the half-hour beginning 75 minutes before sunup. (Venus doesn’t rise until 45 minutes before sunrise on Dec. 1; 30 minutes before on Dec. 12; and only 15 minutes before sunrise on Dec. 23.) Binoculars are increasingly useful for spotting Venus before sunup on the last possible date before superior conjunction, beyond the sun on Jan. 9.

Next in prominence after Jupiter are twinkling blue-white Sirius in the southwest to west-southwest, until it sinks from view late in the month; golden Arcturus high in the east; blue-white Vega rising higher in the northeast; and Capella sinking in the northwest. Mercury, very low in the east-southeast to southeast, attains magnitude +1 by Dec. 20, and magnitude 0 by Dec. 24, and for the rest of month ranks second in brilliance, after only Jupiter, since Sirius has departed.

Other bright morning objects include the Winter Hexagon, which has Sirius and Capella marking its southern and northern vertices, and red Betelgeuse inside. But Rigel, Aldebaran, Sirius and Betelgeuse exit the morning sky in December, leaving only the upper arch of Procyon, Pollux (with Castor 4.5 degrees to its right, not shown) and Capella.

Regulus, heart of Leo, is high in the southwest to west-southwest following the Hex across the sky. I like to imagine Leo chasing his menu, which includes some beef (Aldebaran in Taurus), two dogs (Sirius and Procyon in Canis Major and Canis Minor), a mother goat (Capella in Auriga) and even some human fare (Rigel and Betelgeuse of Orion, the Hunter, becoming the Hunted; and Pollux and Castor, of Gemini, the Twins).

Following Regulus across the sky are Arcturus and Spica. The latter star marks the ear of grain in the hand of Virgo, the next zodiac constellation east of Leo. The zodiac constellations serve as hosts to the bright objects of the solar system, namely the sun, moon and planets.

On Dec. 1, dim red Mars appears just 3 degrees from Spica and 16 degrees to the upper right of Jupiter. Jupiter itself is 4 degrees west-northwest of the third-magnitude star Alpha in Libra on Dec. 1; within 1 degree of that star Dec. 18-26; and as close as 0.7 degrees from Alpha Lib on Dec. 21-23. On Dec. 31, Mars is 3 degrees to the upper right of Jupiter, and 20 degrees to the lower left of Spica. On the last morning of 2017, Alpha Lib lies nearly midway between the planets, 1.5 degrees from Mars and 1.7 degrees from Jupiter—a beautiful sight for binoculars! The star’s Arabic name, Zubenelgenubi, meaning “Southern Claw,” refers to its assignment to a larger early version of the Scorpion, the next zodiacal constellation east of Libra. The pairing of Jupiter with Alpha Lib on Dec. 22 is the first of a triple conjunction between them. Jupiter, retrograding, will pass closely north of the star on June 3, 2018, and then, after resuming direct (eastward) motion, will pass closely north of it a third time, on Aug. 15.

Mercury, pulling away from its inferior conjunction of Dec. 12, brightens rapidly in the morning sky and holds a steady 28 degrees to the lower left of Jupiter Dec. 21-27. Look 8 degrees to the upper left of Antares, heart of the Scorpion, Dec. 20-27. During Dec. 28-30, Mercury is 9 degrees to the left or lower left of Antares. On Dec. 31, Mercury is 31 degrees to the lower left of Jupiter and 10 degrees to the lower left of Antares. On New Year’s morning, Mercury reaches greatest elongation, 23 degrees from the sun. On the mornings of Jan. 6 and 7, Mars will appear only 0.3 degrees from Jupiter. Within a week later, on Jan. 13, Mercury will pass 0.8 degrees south of Saturn. Wouldn’t a good pair of binoculars to view these events make a great gift for a skywatcher?

December opens with a few brightly moonlit nights. On Saturday evening, Dec. 2, the moon rises 20 minutes before sunset and is nearly full. An hour after sunset, find the Pleiades 10 degrees to the moon’s upper left, and Aldebaran, whose name means “the Follower” (of the Pleiades), within 14 degrees below the Pleiades and 7 degrees to the moon’s lower left. The moon creeps closer to Aldebaran throughout that night. During morning twilight on Sunday, Dec. 3, use binoculars to spot Aldebaran very close to the moon’s upper left. A “supermoon,” the closest full moon of 2017, occurs at 7:47 a.m. that morning, just more than an hour after moonset in Palm Springs. The moon reaches its least distance from Earth just 17 hours later, at 12:46 a.m. on Dec. 4.

Moonrise early on Sunday evening, Dec. 3 (as seen from Palm Springs), occurs at 5:11 p.m. Although more than nine hours past full, the moon, rising 33 minutes after sunset, will be impressive. Note Aldebaran 8 degrees to the moon’s upper right.

After it’s full, moonrise occurs later each night: On Monday, Dec. 4 at 6:10 p.m.; on Dec. 5 at 7:13 p.m. (northernmost moonrise of the month); on Dec. 6 at 8:19 p.m.; on Dec. 7 at 9:25 p.m.; and on Dec. 8 at 10:30 p.m.

On Dec. 5, two weeks have elapsed since Nov. 21, when Earth passed between the sun and the Pleiades (Seven Sisters) star cluster. Starting on Dec. 5, the moon is well below the horizon at the end of evening twilight, nearly 1 1/2 hours after sunset, and the sky is then dark and moonless. Starting on the evening of Dec. 5, face east-northeast to east at dusk and watch the Pleiades emerge and ascend in the deepening twilight. The scene is well described in lines by Alfred Lord Tennyson.

After the full moon, you can follow its motion in the morning sky, averaging 13 degrees per day eastward through the constellations of the zodiac. Watch the waning gibbous moon pass 9 degrees south of Pollux on Dec. 6, and leapfrog over Regulus on Dec. 8 and 9. On Dec. 12, find the waning crescent moon 9 degrees above Spica. On Dec. 13, the moon is 4 degrees to the upper left of Mars and 9 degrees to the lower left of Spica.

The moon rises very late on the night of Dec. 13 (as a 13 percent crescent at 3:21 a.m. on Dec. 14), leaving the peak of the Geminid meteor shower, overnight on Dec. 13-14, excellent for viewing meteors. Best hours are from Wednesday at 9 p.m. until first light of dawn at 5:15 a.m. on Thursday, although a few long trails from meteors grazing Earth’s atmosphere might be seen anywhere in the sky as Castor, near the shower’s radiant, rises soon after 6 p.m.

On the morning of Dec. 14, perhaps after a few good hours of meteor-watching, look for the moon passing 4 degrees north of Jupiter. On Dec. 15, find the moon within 12 degrees to the lower left of Jupiter. On the 16th, the last easy old crescent moon will appear 23 degrees to the lower left of Jupiter. If you have a very good low horizon between east-southeast and southeast, use binoculars to find Antares rising 9 degrees to the lower right of the crescent moon in brightening morning twilight.

In case the sky is very clear just after 6 a.m. on the morning of Sunday, Dec. 17, we have a site selected in northwestern Palm Springs to attempt a sighting of a very old moon, just a little more than 16 hours before new. We’ll announce the details in the “Impromptu Star Parties” link mentioned below.

We’re still checking out sites in Desert Hot Springs and the eastern Coachella Valley to attempt a sighting of a very young moon shortly after 5 p.m. on Monday, Dec. 18. The moon’s age will be just more than 18.5 hours. As the date draws near, visit the same link for details. Twelve days later, on Saturday, Dec. 30, the daytime waxing gibbous moon rising at 2:53 p.m. is covering Aldebaran. Telescopes may show the star emerging along the moon’s bright edge at 3:51 p.m.

The website of the Astronomical Society of the Desert, at www.astrorx.org, has a listing of our evening star parties at two locations. The primary, more-accessible location is at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument (on Highway 74, within four miles south of Highway 111 in Palm Desert). A session is scheduled there on Saturday, Dec. 23, from 5-8 p.m. Sawmill Trailhead, our high-altitude site (elevation 4,000 feet—wear warm clothes), will have a star party starting at dusk on Saturday, Dec. 9. The society’s website includes maps and directions for both locations. Star parties can be cancelled in poor observing weather. See the link to “Impromptu Star Parties” on that website.

On Friday, Jan. 5, I will present a summary of the coming year’s sky events. The summer and early autumn of 2018 will be outstanding for viewing planets in the evening sky, and there will be total lunar eclipses in January 2018 and January 2019. The talk will be held at the Portola Community Center, 45480 Portola Ave., in Palm Desert. Doors open at 6:30 p.m. for refreshments, and the talk begins at 7 p.m.

Also, check out the Sky’s the Limit Observatory and Nature Center in Twentynine Palms, at skysthelimit29.org.

Wishing you clear skies!

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing sky watching opportunities for a variety of groups in the Coachella Valley. Robert D. Miller did graduate work in planetarium science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.

Published in Astronomy

Brilliant Venus (magnitude -4.0) and fainter Saturn ( +0.5) are 4.5 degrees apart in the southwest at dusk on Nov. 1, but Venus speeds away while Saturn sinks into the solar glare, widening the gap between them to nearly 15 degrees by Nov. 11, and to 22 degrees by Nov. 18. Use binoculars to watch Venus pass background stars in Ophiuchus and Sagittarius on Nov. 4, 16, 17, and 22. Venus sets farthest south Nov. 14. By month’s end, Venus brightens to magnitude -4.2 and is noticeably higher than it was at the start of November. A telescope shows Venus in gibbous phase, 70 percent full at month’s end. Wonderful changes will happen in coming months, before Venus departs from the evening sky in late March.

Mercury (magnitude -0.5) passes 3.5 degrees south (to the lower left) of Saturn on Nov. 23, but they’ll both be very low in the twilight glow, with Mercury brighter. Using binoculars, look 27 degrees to the lower right of Venus. Replacing Saturn, Mercury is 25 degrees to the lower right of Venus on Nov. 30, and will hold 24 degrees to the lower right of Venus Dec. 2-12.

Look for dim Mars (magnitude +0. 4 to +0.6) in the south to south-southwest, to the upper left of Venus, by 37 degrees on Nov. 1; 30 degrees on Nov. 16; and 24 degrees on Nov. 30. Watch Mars pass third- and fourth-magnitude stars in Capricornus, the sea-goat, on Nov. 14 and 27, and on Dec. 10.

In the morning sky in the east-southeast to southeast, find bright Jupiter, magnitude -1.7 to -1.8. As the sun withdraws east of Jupiter this month because of Earth’s faster revolution around the sun, the giant planet ascends higher in predawn. Note the first-magnitude star Spica in Virgo, 13 degrees to 8 degrees below bright Jupiter.

The moon, as a waxing crescent in evening sky, can be seen in a pretty gathering with Venus and Saturn on Nov. 2; near Mars on Nov. 5 and 6; near Mercury on Nov. 30; near Venus on Dec. 2 and 3; and near Mars on Dec. 4 and 5. In the mornings, follow the waning moon, near Aldebaran, eye of Taurus, on Nov. 15; near Pollux, brighter of the Gemini twins, on Nov. 18; near Regulus, heart of Leo, on Nov. 21; near Jupiter on Nov. 24; and near Spica and Jupiter on Nov. 25.

The full moon, on Monday, Nov. 14, at 5:52 a.m., follows the moon’s perigee (closest approach to Earth) by only 2.5 hours. The resulting “Supermoon” is the closest until Nov. 25, 2034. (Get ready for the inevitable hype in the news media!) The next “Supermoon” closer than that one will occur on Dec. 6, 2052—the best of the 21st century. The moon this month will be closest for observers in the Coachella Valley on the night of Sunday, Nov. 13, just a few minutes after the moon reaches its highest point in the south, at 11:20 p.m., and, contrary to appearances, not when the moon is rising on Sunday around 4:33 p.m. or setting Monday morning around 6:11 a.m. (The moon just seems larger at rising or setting than when it is high in the sky. It’s called the “moon illusion.”) Also, this is not the brightest full moon of this year. That’s because this month’s full moon passes widely south of Earth’s shadow, and does not reflect as much light toward us as it would if the moon narrowly missed the shadow. The sharp brightening of the moon or an asteroid when it appears almost exactly 180 degrees from the sun is sometimes called “the opposition effect,” or “opposition surge.”

Star parties provide wonderful opportunities to join with other folks who love to share their interest in observing the sky, and to get great views of astronomical objects through a variety of binoculars and telescopes. The first two events, happening this weekend, are annual gatherings not far from the Coachella Valley: The 2016 Nightfall Star Party takes in Borrego Springs Oct. 27-30, while the 2016 Joshua Tree National Park Night Sky Festival is Oct. 28-30.

Local star parties (in and near the Coachella Valley): The Astronomical Society of the Desert will host the next of our series of monthly star parties on Saturday, Nov. 5, from 6 to 9 p.m., and on Saturday, Dec. 17, from 5 to 8 p.m. They are held at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument, on Highway 74, within four miles south of Highway 111 in Palm Desert. Check the society’s website at www.astrorx.org for listings of our regular star parties at the Visitor Center, and our high altitude star parties at Sawmill Trailhead starting at dusk. The next high-altitude star parties (at 4,000 feet—wear warm clothes!) will be held on Saturday, Nov. 19, and on Saturday, Dec. 3. Follow links to maps and directions to both star party sites, and for dates and locations of lecture meetings. Also, check the link to our “Impromptu Star Parties,” which could be announced on short notice at any time.

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. Robert D. Miller did graduate work in planetarium science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.

Published in Astronomy

The full moon occurs on Sunday, Aug. 10, at 11:09 a.m. The moon passes perigee—221,765 miles from Earth, the closest approach of the year—at the same hour.

But this “supermoon,” visible at dawn and dusk on that date, is not the brightest moon of 2014, because of the phase effect, which makes the moon’s brightness decrease sharply when it’s a few degrees away from being exactly 180 degrees from the sun. You can duplicate this effect one night by standing between a stationary bright-light source and a highly reflective road sign, so that the shadow of your head is cast upon the sign. Note how the sign really lights up around your head’s shadow, giving the shadow a brilliant “halo.” However, if you take a step or two to left or right, you’ll notice how quickly the road sign fades away.

August's full moon passes four to five degrees north of Earth’s shadow center, causing the moon to set after sunrise and rise before sunset on Aug. 10. Further, the timing of the full moon, during the daytime, places the moon widely northwest of the Earth’s shadow at sunrise, and northeast of it at sunset.

Even with the moon not as bright as could be, there are no truly dark skies between dawn’s first light on Aug. 8 and nightfall on Aug. 14. This fact will largely spoil this year’s Perseid meteor shower, which would otherwise be at its best in the predawn darkness hours of Wednesday, Aug. 13.

If you’re outdoors that morning as twilight brightens, watch for Jupiter rising in the east-northeast, 5 degrees to the lower left of Venus. Venus goes east against background stars by 1.2 degrees per day compared to Jupiter’s 0.2 degrees; watch their separation narrow by about 1 degree daily.

Don’t miss the spectacular pairing of Venus and Jupiter on Monday, Aug. 18, within 0.4 degrees. Five days later, on Saturday, Aug. 23, the old crescent moon joins the brilliant planets in a beautiful scene.

Evening planets: Find the planets Mars and Saturn in the southwest at nightfall, and compare them in brightness and color to each other; to bluish Spica, to their lower right; and to reddish Antares, to Saturn’s left. The stars will twinkle noticeably.

Watch the Mars-Saturn gap shrink until they’re 3.4 degrees apart on Aug. 25, and then widen to 5.0 degrees apart by Aug. 31. The moon will appear near these planets on Aug. 31.

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs.

Published in Astronomy