SKY REPORTER: Winter Wondersky

The Great Nebula in Orion.
Credit: R. Villaverde, Hubble Legacy Archive, NASA

The holiday season is heralded by a magnificent array of celestial lights centered on the constellation Orion with its glorious pair of exceptional stars, tinted supergiant Betelgeuse, and blue-white Rigel.  Orion represents the great mythological Hunter—sky nemesis of Taurus and companion of Diana, goddess of the Moon.

Evening skies are graced by Orion’s arrival soon after sunset, and throughout the nights of December this majestic figure travels westward across our southern sky. On many levels, cosmic treasures in and around Orion delight our eyes and trigger the imagination.

Perhaps the best place for a novice to begin exploring the winter evening sky is the striking threesome of stars representing Orion’s Belt. They’re not the brightest above our horizon but are distinguished by their elegant line with Alnitak to the left, Mintaka on the right, and Alnilam between them. Framing this cynosure are four principal stars outlining the Hunter’s frame. This set is highlighted by orange-yellow first magnitude Betelgeuse on the top left and even brighter bluish-white Rigel at the lower right of the giant’s figure.   

Just south of the Belt is one of the most remarkable sites in the entire sky. Known variously as the Great Nebula in Orion, Messier 42, and the Orion star factory, it’s a vast cloud of glowing gas, dust, and stars. It’s seen with unaided eyes as a fuzzy star if the night is clear and dark. Optical and photographic enhancements reveal rich allure of the Nebula’s magnificent, turbulent swirls.

Just beyond Orion’s borders, sky neighbors offer a smorgasbord of visual treats. The unmatched sparkle of Sirius, brightest star in the night sky, immediately captivates when we trace our line of sight along a path extending down to the left of the Belt stars. Viewing in the opposite direction brings us to the giant star Aldebaran, representing the fiery eye of Taurus. Other winter sky delights beckon including telescopic views of the fine multiple star Castor in Gemini and binocular and small telescope sights of a sparkling array of stars set amid soft reflected glow in the Pleiades star cluster of Taurus.

Whether viewing with unaided eyes, binoculars, small telescopes, or substantial observatory instruments, winter nights present wonders all the more remarkable because we experience those objects via first-hand contact with their far travelled beams of light.

If you don’t have a telescope, but the idea is appealing for yourself or as a gift, I suggest first using binoculars to explore the night sky for a few months with a good guide book in hand, scouting and identifying bright planets and stars. It will then be lots more fun handling, and enjoying a good telescope after you have spent a while exploring the heavens with binoculars.  Excellent practical advice to savor before buying your telescope may be found on Ed Ting’s telescope review website.

For a heads-up about sky treats this winter season, we’ll be exploring the celestial scene in the Hayden Planetarium Space Theater Monday evening December 15 beginning 6:30 p.m. Later while we’re enjoying our hot chocolate and, if the sky is clear, the Amateur Astronomers Association will have telescopes poised outside showing sights above. Be sure to bring binoculars for the dome and outdoors if we have a clear night.

The Moon

The Planets

Until the last week in December, when it might be seen low in the southwestern sky during evening twilight, Mercury is too close to the Sun’s glare to be noticed. Venus is quite low in that part of the sky, but its brilliancy and greater angular distance from the Sun allow us to spot it without much difficulty. Rusty, first magnitude Mars is also in the southwestern evening sky this month. It remains above the horizon for about three hours after evening twilight.

On Tuesday December 9, Jupiter begins its annual retrograde motion whereby the big planet reverses its apparent motion relative to “fixed” background stars. For several months it will seem to move gradually westward relative to those stars. Similar motions of Mars, Jupiter, and Saturn vexed ancient astronomers and astrologers as they tried to predict locations of the planets. Eventually complex geocentric models of the heavens, although incorrectly assuming Earth to be at the center of the cosmos, did provide fairly accurate predictions of planet positions. Those models were totally at variance with the reality of planets orbiting the Sun.

The night of Thursday December 11 the waning gibbous Moon is about six degrees of arc to the southeast of Jupiter and a similar distance from first magnitude star Regulus, brightest in Leo.

Saturn is currently emerging from early morning twilight and may be seen for several pre-dawn hours low in the southeast.

December 13 is the peak of the Geminid Meteor Shower. About one meteor trail per minute may be expected, appearing to radiate from a direction in the sky near the star Castor in the constellation Gemini.

Sunday December 21 is the start of winter in the northern hemisphere and the shortest day in our year. At 6:03 p.m. Eastern Time the Sun is directly overhead a point in the Pacific Ocean on the Tropic of Capricorn about 730 miles South-Southeast of American Samoa.

A lovely young crescent Moon may be seen toward the southwest near Mars in Capricornus early on Christmas Eve and Christmas night.

As the year approaches its conclusion, Mercury may be seen less than four degrees of arc from much brighter Venus early on the evening of December 30. At the end of civil twilight at about five p.m. Mercury appears below Venus and a few degrees of arc above the southwest horizon.