Night Lights: December sky offers gift of good gazing

Graphic courtesy of Andy Veh. Jupiter is in retrograde motion, appearing to move from left to right through Gemini in December and January.

Graphic courtesy of Andy Veh. Jupiter is in retrograde motion, appearing to move from left to right through Gemini in December and January.

By Andy Veh, for the Redoubt Reporter

Rising in the east and gaining altitude throughout the next two months are the great winter constellations. One is Orion with seven bright stars, among them red Betelgeuse and blue Rigel and its stellar nursery, the Orion nebula.

Then there’s Taurus with red Aldebaran and its prominent star cluster, the Pleiades, and Auriga with yellow Capella. Gemini with the twin stars Castor and Pollux can be seen, as can the head of Canis Major with the brightest star (aside from the sun) that we can see from Earth, Sirius. There’s also Procyon in tiny Canis Minor and, very late in the evening, Regulus in Leo.

This is my favorite region of the sky, because it holds seven of the 20 brightest stars as seen from Earth, and because it contains quite a few easily recognizable constellations.

High in the south is the Great Square of Pegasus in the shape of a diamond. Above it, close to the zenith, is Cassiopeia. Getting close to the western horizon — but never completely setting in Alaska — are the three stars that make up the summer triangle, Deneb in Cygnus, Vega in Lyra and Altair in Aquila (that one actually does set — just barely, for a few hours).

In the north are Ursa Major’s Big Dipper and Ursa Minor’s Little Dipper, the latter always really close to 60 degrees, our latitude on the Kenai.

Several planets are visible in the evening and the rest of the night. Quite-bright Jupiter rises in the northeast in the early evening, becoming particularly prominent around 9 p.m. This winter it appears in Gemini, making a nice triangle with Pollux and its fainter twin, Castor.

Jupiter is in retrograde motion (an optical illusion caused by Earth’s orbit) this month, seemingly moving from Pollux to the fainter Alhena (one of Gemini’s feet) to its right until it’s smack in the middle between these two by the end of the month.

That motion continues through January and February. In March and April we will have passed Jupiter enough that we can see its regular motion, back toward Pollux. Look for the full moon right next to the giant planet Dec. 17 and 18.

Uranus and Neptune can still be seen in the evening but they require finder chart. (I recommend Googling them.)

Other planets are visible in the early morning. Mars rises in the east around 1 a.m., gaining altitude during the night and shining prominently reddish in the south near Leo by the time we get our kids to school. It is moving rapidly from Leo toward Virgo’s bright Spica, which it will join in early February. The third-quarter moon joins the red planet on Christmas Day.

Saturn rises around 5 a.m. in the southeast. During dawn, draw an imaginary line from Jupiter through Mars and continue until you get to the last bright object above the southern horizon — that’s Saturn. The crescent moon is near the ringed planet Dec. 28.

Venus cannot be seen until fall 2014, when it will appear in the morning sky.

All other planets — Mercury, Mars, Uranus and Neptune — appear too close to the sun, so that they can’t be seen against the bright daytime sky.

You may have read about comet ISON. Unfortunately, it disintegrated due to solar heat at its perihelion, coming within two solar radii to the sun’s 10,400-degree F atmosphere. There had been a faint glimmer of a dust tail reappearing, prompting Phil Plait of Slate magazine calling it the “undead maybe somewhat ex-comet.” (Phil is the author of the very good Bad Astronomy website.)

The winter solstice is Dec. 21, when the northern hemisphere’s axis points away from the sun, giving us the shortest day (with the sun about five hours above the horizon) and the lowest sun in the sky at only 7 degrees above the southern horizon at noon.

The low altitude of the sun (spreading its radiation out across the landscape) and the short duration combine to give us low temperatures during winter. Our closest approach to the sun Jan. 4 is not enough to alleviate that.

Andy Veh is an associate professor of physics, math and astronomy at Kenai Peninsula College.


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