Page 77 - Astronomy - October 2017 USA

SOUTHERN

SKY as it appears in Earth’s southern sky.
MARTIN GEORGE describes the solar system’s changing landscape

December 2017: Mars and Jupiter rule

December begins with a pair Mars moves eastward at a into view. A telescope reveals a Cetus. Aim your binoculars 7°
of planets hanging low in the good clip relative to the back- disk that spans 7" and appears south and a bit east of Diphda.
west-southwest during evening ground stars, crossing from slightly more than half-lit. (Seven degrees is a typical field
twilight. Mercury shines at Virgo into Libra in late Venus hides in the Sun’s of view through 7x50 binocu-
magnitude –0.1 and will be far December. It then rises 3.5 glare all month. It will pass lars.) This carries us across the
easier to spot than its sibling, hours before the Sun and on the far side of the Sun in border into Sculptor, where we
magnitude 0.5 Saturn. The stands 25° high at the start of January and return to view find the splendid Silver Coin
innermost planet lies 9° high twilight. Still, its better posi- in the evening sky in early Galaxy (NGC 253). This almost
45 minutes after sunset on the tion doesn’t translate into good autumn. edge-on spiral is not a difficult
1st and appears 3° to the ringed views through a telescope. Even The starry sky binocular object under a dark
planet’s upper left. Mercury on the 31st, the Red Planet sky, and you should see it as a
reached greatest eastern elon- shows a featureless disk just 5" We’re all busy in December, short streak of light. Caroline
gation in the final week of in diameter. whether preparing for the holi- Herschel, William Herschel’s
November, but it is now sink- Jupiter also resides in the day season or attending all of sister, discovered this object
ing rapidly toward the Sun on morning sky. It rises 90 min- those end-of-the-year parties. in 1783.
the way to its December 13 utes before the Sun in early With summer’s late sunsets About 2° southeast of
inferior conjunction. Target December, when it appears upon us and the extra hour NGC 253 lies globular cluster
it through a telescope in the about 15° to Mars’ lower right. of summer time observed in NGC 288. This loosely concen-
month’s first few days and Unlike Mars, however, Jupiter many places, it’s a great oppor- trated object, discovered by
you’ll be rewarded with nice shines brightly. Gleaming at tunity to pop outside with William Herschel in 1785,
views of an 8"-diameter, magnitude –1.7, it’s the bright- binoculars after an evening glows at 8th magnitude.
crescent-shaped disk. est point of light in the night barbecue to admire the sights Now shift your gaze 17°
Because Saturn glows more sky. Jupiter lies in Libra and of December’s night sky. Keep farther south to the 2nd-
faintly and stands deeper in the moves eastward as well, though in mind that the lights of the magnitude star Ankaa (Alpha
twilight, it is much harder to more slowly than Mars. By the city will make these objects [α] Phoenicis). Scan 4° north-
view. Although binoculars end of December, the two plan- harder to view. west and see if you can spot
should reveal the pair, you’ll be ets have closed to within 3° of Although many people NGC 55. This is another edge-
hard-pressed to spot the ringed each other. don’t consider the variable star on spiral in Sculptor, but it’s
planet with your naked eye. Jupiter still lies fairly low W Orionis spectacular, it’s one harder to spot than NGC 253.
And a telescope likely won’t in the sky, so it won’t appear of my favorite objects. I find The last three objects I men-
show much detail because tur- supersharp through a tele- this deeply red star quite strik- tioned are best suited to dark
bulence in Earth’s atmosphere scope. By month’s end, how- ing. To locate it, start at 2nd- country skies, so let’s wrap up
distorts the image. Saturn ever, you should be able to magnitude Mintaka (Delta [δ] our tour with an easy one. Go
passes on the far side of the discern its two dark equatorial Ori), the westernmost star in back to Orion, trace a line
Sun on December 21 and won’t belts on a disk that spans 33". Orion’s famous belt. Using through its belt stars, and then
return to view until January. Our final planet is none binoculars, scan westward extend this line to the south-
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You’ll need to wait until the other than Mercury. After toward 4th-magnitude Pi (π ) east. You’ll immediately see
other end of the night to see passing between the Sun and Ori, the southernmost star in brilliant Sirius, Canis Major’s
another bright planet. Mars Earth at inferior conjunction, Orion’s shield. You’ll find W luminary and the night sky’s
rises about two hours before the innermost planet climbs about 80 percent of the way to brightest star. Scan 4° due
the Sun in early December. rapidly into the predawn sky Pi . Visually, W varies between south of Sirius and you’ll land
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Look for its ruddy glow in the by the end of December. On magnitudes 6 and 8 over a on the splendid open star clus-
eastern sky soon after. If you the 31st, it stands 8° high in period that averages about ter M41. If it helps you figure
don’t see it right away, first find the east-southeast 45 minutes 200 days. out directions, remember that
1st-magnitude Spica, the blue- before sunup. Shining at mag- To find the next group M41 lies about one-third of the
white luminary of Virgo. Mars nitude –0.3, it should be easy to of objects, swing around to way from Sirius to magnitude
lies 3° below Spica. At magni- pick out of the twilight glow. If the west and zero in on 2nd- 1.5 Adhara (Epsilon [ε] Canis
tude 1.7, the planet glows half you don’t see the planet right magnitude Diphda (Beta [β] Majoris), the Big Dog’s second-
as bright as the star. away, binoculars will bring it Ceti), the brightest star in brightest star.