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Winter sky provides brilliant views

The Sky Guy

Posted: Sunday, December 02, 2007

 

 

The recurring spectacle starts between 7 and 8 p.m. every day in December. That's when a brilliant winter sky starts rising in the east: along with Orion's Betelgeuse and Rigel, its belt and sword, Canis Major's Sirius and Canis Minor's Procyon, Gemini's Castor and Pollux, Cancer's Praesepe cluster, Auriga's Capella, Taurus' Aldebaran, Hyades and Pleiades clusters, the planet Mars glows reddish among them.

Mars is closest to Earth on Dec. 18 at 54 million miles but of course presents great views all month long. Together with the two red giant stars Betelgeuse and Aldebaran, Mars is producing a great triangle.

Somewhat later in the evening, Leo's Regulus and the planet Saturn are rising. To include those two the diagram shows the sky around 11 p.m., when everything moved to the South. I used the free shareware "Stellarium," and the snow-covered mountains are actually the Olympic Range in Washington as a possible landscape in the software.

The full moon can be seen very close to Mars on the 23rd, the waning thrid quarter moon is close to Saturn on the 27th and 28th.

Looking elsewhere in the early evening, but not pictured in the diagram, are the constellations and stars in the north: Ursa Major above the horizon, Ursa Minor quite high; in the West: Cygnus' Deneb, Lyra's Vega, Aquila's Altair, Delphinus; near the Zenith: Cassiopeia, Cepheus, Pegasus, Andromeda, and Perseus.

Venus remains the main staple in the morning sky, rising around 8 a.m. in the east. If you happen to drive east on the Sterling Highway at that time, it's Venus that you see; it appears together with a waning crescent moon on the 4th.

The other planets, Mercury, Jupiter, Uranus, Neptune, and Pluto, are either on the other side of the sun or lost in the glare of twilight.

The Geminid meteor shower peaks during the nights of Dec. 13 and 14 with an expected average of about 20 meteors per hour; the radiant as the name suggests lies in Gemini, so it looks as if the meteors are emanating from Castor, Pollux and Mars. It's also the only major meteor shower that is associated with an asteroid, Phaethon, rather than a comet.

Comet 17P/Holmes is still a faint fuzz ball near Perseus' brightest star Mirfak, between Auriga's Pentagon and Cassiopeia's W, and can be spotted with binoculars (for finder charts I recommend skyandtelescope.com).

While the winter solstice occurs as expected on Dec. 22, the earliest sunset is already on the 8th and the latest sunrise on Jan. 5. Since Earth is closest to the sun on Jan. 3 at 91.5 million miles (it's farthest on July 4 at 94.5 million miles), it orbits a little faster this has to do with Kepler's second law, which is due to the conservation of angular momentum, and which is also responsible for a figure skater spinning faster upon pulling in his or her arms during a pirouette and therefore the day (from one noon to the next noon) is, at 24 hours, 28 seconds, about half a minute longer than the average day (by definition 24 hours, 0 minutes).

Since clocks are kept at a constant 24 hours, this combined effect places the earliest sunset two weeks earlier than the solstice and the latest sunrise two weeks later.

Andy Veh is an assistant professor of physics and mathematics at Kenai Peninsula College.



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