The Night Sky

The Night Sky A Celestial Spectacular Month In the upcoming month of December 2013, the night sky will put on a spectacular show with bright planets in the evenings and a possible bright comet in the early morning sky. I am sure many of you have noticed the very bright star-like object low in the southwestern sky after sunset. This is the planet Venus which is now shining at its maximum brightness. On December 5th, Venus shines to the lower left of crescent moon. With each passing day this month, Venus gets bigger and more crescent shaped in a telescope as it sets earlier and earlier. Sharp-eyed observers may be able to barely make out this crescent shape with the naked-eye on the evenings between Christmas and New Years Day. If you are unable to see this crescent, you will easily be able to see it through binoculars. In early December, bright Jupiter rises on the northeastern horizon just as evening twilight is ending. On the nights of December 9th and 10th, Jupiter shines just to the east of Delta Geminorum. During the following week, a nearly full moon passes just to the south of Jupiter on December 18th. By the month’s end, Jupiter will rise just ½ hour after sunset. A little over 4 hours after Jupiter rises, the red planet Mars will rise due east. During the first week of the month, Mars will be very close to Beta Virginis, while during the last few days of the year, Mars will be very close to Gamma Virginis as it rapidly moves through this constellation. During this time period, Mars brightens by about 30%. The astronomical fun continues a few hours prior to dawn. During the first week of the month, Mercury, Saturn, and perhaps Comet ISON will be visible low in the east an hour before sunrise. On December 1st, a crescent moon shines a little below Saturn and to the upper right of Mercury low in the southeast 60 to 30 minutes before sunrise. Comet ISON may be visible to their left. Four days later on December 5th, Comet ISON forms an equilateral triangle with Saturn and Mercury, where Mercury will be the lowest of the three. As mentioned last month, Comet ISON passes to within a solar diameter of the sun on Thanksgiving Day. This comet has been very faint throughout first part of November; however on November 14th, Comet ISON flared to naked-eye visibility, though still relatively faint. A long tail started to develop during November as well and continues to lengthen. The nucleus of this comet will likely fragment during this close encounter with the sun and the date of this fragmentation will determine the brightness of this comet during the first week of December. Should Comet ISON fragment prior to closest approach to the sun (perihelion), this comet may not be visible in early December. If however it fragments at perihelion or shortly thereafter, Comet ISON may be spectacular in the early morning sky prior to sunrise. This is what happened to Comet West in 1976, which was a dazzling sight in the eastern morning sky that spring. If you are not an early riser, I encourage you to go out an hour or so before sunrise to see this possibly bright comet. The moon will be full at 4:28 a.m. on the morning of December 17th. According to folklore, the December full moon is known as the Full Cold Moon. Unfortunately, the Geminid meteor shower peaks three days prior to that date which means we are unlikely to see many Geminids in the bright moonlit sky. Finally, the winter solstice occurs at 12:11 p.m. on December 21st. This marks the lowest point on the sky that the sun reaches and corresponds to the fewest number daylight hours of the year. This also marks the first day of winter in the northern hemisphere. The free public astronomy open houses at the ETSU Powell Observatory take a hiatus over the holiday break. They will resume on February 8, 2014. Further information about these open houses can be found on the web at http://www.etsu.edu/cas/physics/observatory/default.aspx. This month’s Night Sky was written by Dr. Donald G. Luttermoser, Chair of the Department of Physics and Astronomy. He can be reached at [email protected]. Astronomy-related information for the public, including a link to the ETSU Powell Observatory, can be found at http://www.etsu.edu/cas/physics/outreach/astronomy.aspx. .

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