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The Sky This Week, 2016 December 27 - 2017 January 3

So long, 2016. Wait a sec...
Orion and vicinity, New Year's 2016
imaged from Morattico, VA with a Canon EOS Rebel T2i DSLR

The Moon returns to the evening sky to greet the onset of 2017. New Moon occurs on December 29th at 1:53 am Eastern Standard Time. You’ll find Luna within five degrees of dazzling Venus on the evening of January 1st. On the following couple of nights she dances with the red planet Mars.

By now many of you might have noticed that it’s not quite as dark at 5:00 pm as it was a few weeks ago. You are not being deceived: sunset now occurs about 10 minutes later than it did back on December 7th. However, the total length of day is only three minutes longer than it was on the solstice. The discrepancy occurs because we have yet to experience the year’s latest sunrise. Here in Washington that won’t occur until January 4th, when Old Sol crests the eastern horizon at 7:27 am EST. It also happens that on that day the Earth is closest to the Sun, but we’ll look into this in more detail next week.

2016 will certainly go down as one filled with notoriety. It is probably not too much of a stretch of the imagination to say that a great many people will be more than happy to see it end. That being said, 2016 will drag on for just a bit longer than most other years. Yes, it has already stretched an extra day in length thanks to the rules of the Gregorian Calendar which deem it to be a leap-year, but thanks to our modern precision timekeeping methods it will get one extra second added to its length in the last minute before the strike of 00 hours, 00 minutes, and 00 seconds Coordinated Universal Time (UTC) on January 1st, 2017. This "leap second" is necessary due to the gradual slowing of the Earth’s rotation when compared to the ultra-precise atomic time scale known as International Atomic Time (TAI) that is now observed around the globe. Since 1972 our civil time has been based on TAI, whose second is defined by a very precise atomic frequency. This time-scale exists coincidentally with another, known as UT1, which closely mirrors the length of the mean time between successive transits of the Sun over a standard meridian. Currently the difference between these two time-scales amounts to about 0.0015 to 0.002 seconds per day, resulting in a cumulative difference between TAI and UT1 of one second over the span of a few years, and when the difference approaches one full second a "leap second" is inserted to coordinate the two time-scales for another few years. The actual date of insertion for a given "leap second" is based on observations carried out in part by the USNO’s Earth Orientation Department, which keeps close tabs on how the Earth rotates with respect to a distant reference frame made up of thousands of very distant quasars. While 2016 will amount to an extra-log year, at least it won’t be like 1972, which saw the insertion of two "leap seconds" in addition to being a leap year.

Venus continues to command a prominent presence in the western sky at dusk. The dazzling planet sets well over two hours after the end of evening twilight and is gradually increasing in brightness as she approaches greatest elongation from the Sun in another few weeks.

Mars is working his way through the dim constellation of Aquarius, a constellation whose two brightest stars barely reach third magnitude. The red planet is the brightest object after Venus in this part of the sky and is easily found thanks to his warm pinkish hue. The waxing crescent Moon pays a call on both planets as the New Year opens.

Jupiter is now close to the meridian in the south an hour before sunrise. He is gradually closing in on the bright star Spica in the constellation Virgo, and he will spend the 2017 apparition in the general vicinity of the star. With the current late sunrises, you can catch a decent glimpse of him through the telescope at an almost decent hour.


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