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Night Sky

December 2010 Night Sky

—Charlie Christmann

We are in for some great sky watching this month. One prime event for the children will be watching for a fast moving “star” with a bright red color floating above homes and dancing between cities on the evening of the 24th. Some may even hear sleigh bells as the star passes near.

The Geminid Meteors

The winter rival for the summer Perseid shower is the Geminids, radiating from the constellation Gemini. The peak is predicted to occur about 1 a.m. MST on the 14th. This could be great viewing for New Mexicans. Gemini will be almost directly overhead at that time, and the Moon will set around midnight, allowing a darker sky.

The shower is thought to be caused by the dusty trail of what may be an extinct comet—3200 Phaethon. Up to 50 meteors are expected each hour; however, the Geminid meteor shower has been increasing in intensity over the past several years, and it is possible to see up to 150 meteors each hour. The Geminids are considered special because of their multicolored hue. This year, the Geminid meteor shower will begin around December 6th and will continue through December 19th.

Thirty two hundred Phaethon is currently classified as an asteroid. It is unusual for an asteroid to be the source of a meteor shower. There are some that will argue that this object is an extinct comet. It is in a highly elliptical 1.4-year orbit that brings it within 0.15 AU (1.4 million miles) of the Sun. It made its closest recent approach to Earth in December 1997, when it passed within 0.31 AU (28.2 million miles) of our planet.

One of the earliest thoughts was that 3200 Phaethon might occasionally collide with other asteroids as its orbit passed through the asteroid belt just beyond Mars. At first, this hypothesis seemed likely, but more detailed studies cast doubt. The orbits of individual Geminid meteoroids are not consistent with the idea that they broke free while in the asteroid belt. Instead, they appear to have crumbled away as Phaethon passed close to the Sun. In this respect, Phaethon is behaving like a comet. The origin of the Geminids may not be fully understood until future space travelers pay a visit to the asteroid-comet.

Total Eclipse

Yes, we have a total lunar eclipse to enjoy this month. Total lunar eclipses happen around the hours of the full Moon. Since the orbit of the Moon does not line up with the equator, it is tipped at a five-degree angle; the Moon spends most of the time either above or below the plane of Earth’s orbit. Only when the Moon, Earth, and Sun line up with the Moon crossing near the equator in its orbit will an eclipse occur. The timing needs to be right to see a total eclipse; otherwise, only a portion of the Earth’s shadow will intersect the Moon. 

It just so happens the full Moon this month is on the same night as the winter solstice. Beginning on the 20th at 11:32 p.m. MST, the Moon begins entering the Earth’s shadow and will slowly start to darken across its face. Sixty-eight minutes later, at 12:40 a.m. on the 21st, the Moon completely will enter the Earth’s shadow, appearing a ruddy red color. The color is caused by refraction of the Sun’s light through the Earth’s atmosphere. Essentially, we are seeing the effect of all the sunrises and sunsets being reflected by the Moon. The total phase lasts 74 minutes, ending at 1:54 a.m. For the next 66 minutes, the Moon will slowly become brighter. The Moon will finally break free of the Earth’s shadow at 3:01 a.m.

The Planets and Moon

The first of the month will be active for planet sightings.

  • Mercury will be making its reappearance this month in the west. On the 1st, look quick for the planet right above the horizon, 30 minutes after sunset. On the 7th, find Mercury on the horizon seven degrees to the lower right of the Moon 45 minutes after sunset.
  • Venus, too, is reappearing this month. On the 2nd before sunrise, relatively dim Venus will be seven degrees to the upper left of the Moon. Use binoculars to look for its crescent shape.
  • Mars is back in the sky. Look 30 minutes after sunset on the 6th, using binoculars to find the planet less than one degree to the right of the thin crescent Moon.
  • Jupiter is midway up in the western sky after sunset this month.
  • An hour before sunrise on the 28th, find Saturn nine degrees to the upper left of the waxing crescent Moon.
  • Feeling lucky? Look for Uranus just below Jupiter in the west. You’ll need dark skies and good binoculars or a small telescope.
  • The Moon is new at 10:36 a.m. on the 5th and full at 1:13 a.m. on the 21st.
     

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