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The Shortest Day Is the Longest

This time of year a day is 30 seconds longer

Winter officially begins with the solstice Saturday, December 21. At 12:11pm EDT that day, the sun reaches its most southerly declination, standing still above the Tropic of Capricorn. For the roughly 90 percent of the world’s population that lives in the Northern Hemisphere, this is the first day of winter, the day of the longest night and the shortest day of the year.
    We say it is the shortest day of the year, but in truth it is one of the longest days as measured from the time of high noon until high noon the next day. Solar time is not neat and consistent like mean time, or civil time, by which we set our clocks.
    In short, the earth moves at different speeds — in both its own rotation and its orbit around the sun — at different times of the year. Right now we are spinning slower, meaning that the solar day is roughly 30 seconds more than 24 hours. Scientists account for this discrepancy with what’s called the Equation of Time. The difference between solar time and civil time is also why the earliest sunset of the year comes two weeks before winter solstice and the latest sunrise comes two weeks after solstice.
    Winter solstice is, more accurately, the day with the least sunlight. This Saturday we will have only 9 hours 26 minutes of it. Of course for stargazers, that’s more than 14 hours of prime viewing.
    Thursday night, the waning gibbous moon rises a couple hours after sunset. A few degrees above it is bright Jupiter, with the twins of Gemini, Pollux and Castor, nearby. Below and to the right of the moon is the bright star Procyon with brilliant Sirius lower still.
    Friday the moon is amid the mostly indescript stars of Cancer. The exception is a small, fuzzy patch at the center point of the Y-shaped constellation, where the crab’s legs meet its body. Here is the Beehive Cluster, or Praesepe, one of the few open clusters visible to the unaided eye. It was this smudge in the sky on which Galileo focused his early telescope in 1609, revealing “not one star only, but a mass of more than 40 small stars.” Today’s binoculars are more powerful than Galileo’s telescope, so you can see for yourself more than what the great Renaissance thinker saw.
    Saturday and Sunday the moon is near the bright star Regulus of the constellation Leo the lion. After midnight these two days also comes the peak of this year’s Ursid meteor shower. While not a big shower, the Ursids reliably produce five to 10 meteors an hour, and the gibbous moon is far from the radiant, in Ursa Minor, so poses little problem.
    Before dawn Christmas morning and Thursday the 26th, the moon rises with dim, ruddy Mars after midnight.
    As the sun sets, there’s no mistaking Venus low in the southwest. But these are the last nights to see this dazzling evening star, which will soon vanish amid the sun’s glare.