This is Dudley Observatory’s Skywatch Line for Friday, December 26, through Sunday, December 28, written by Alan French. The Moon reaches first quarter Sunday afternoon so a waxing crescent Moon will dominate the early evening sky on Friday and Saturday. Sunday’s Moon will be just over half full. On Friday the Moon will be due south as darkness falls. By Sunday it will be due south at 6:00 pm, when the sky is completely dark, and fifty degrees above the horizon – ideally placed for exploration with binoculars or a telescope. If you have a new telescope, or one that has been sitting in a closet unused, put in your lowest power eyepiece and spend some time enjoying our nearest celestial neighbor. No other sight in the night sky shows as much detail and, although the lunar landscape is unchanging, the changing illumination makes for a dynamic view. As the Moon moves toward full, it is fun to watch the sun rise over craters and mountains, slowly bringing more and more detail into view. The Moon sets, leaving the sky nice and dark, at 10:15 pm Friday, 11:25 Saturday, and 12:11 am Monday morning. The Moon will reach full next Sunday, January 4. Venus has moved back into the evening sky and may be glimpsed just after sunset. The Sun now sets just before 4:30 pm and Venus sets just over an hour later, so you’ll need an unobstructed view to the southwestern horizon, free of clouds, and good timing to catch sight of Venus. Look at 5:00 pm when our sister planet will be just over four degrees above the horizon. During the coming weeks Venus will move higher into the evening sky and become increasingly easier to spot. Venus is called our sister planet because it is almost the same size as Earth. The equatorial diameter of Earth is 7,926 miles, while Venus’s is 7,521 miles. Because of its similar size and distance from the Sun there was once speculation that life might exist on Venus. We now know conditions Venus are far from suitable for sustaining life. The planet has a thick atmosphere of carbon dioxide, so the greenhouse effect traps heat and the surface temperature is a whopping 860 degree Fahrenheit. The atmospheric pressure is 92 times that of Earth at sea level and little light reaches the surface of the planet. Mars continues to grace the early evening sky, lying low in the southwest as darkness falls. Mars is now too far away for good telescopic views, spanning only 4.8 arc seconds. Mars observers generally observe the planet when its apparent size exceeds 10 arc seconds. We get a good view of Mars about every 2 years, when the Earth, on its inside track around the Sun, catches up and passes Mars. We’ll have to wait until May, 2016, for out next chance for good telescopic views of the Red Planet. But it’s still nice to see Mars and think about how much we’ve learned in recent decades with orbiters, landing probes, and rovers.
Posted on: Fri, 26 Dec 2014 00:02:16 +0000
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