First Christmas full moon since 1977

Published 1:59 pm Friday, December 18, 2015

This year, Santa and his reindeer will be able to use the full moon as a big spotlight. For the first time since 1977, we have a full moon on Christmas Day.

Full moons at Christmas don’t happen all that often because of the 19 year cycle of the 29.5 day month of lunar phases, combined with leap years. But it’s happening this year, doing its usual job of whitewashing the night sky. All but the brighter stars and constellations get washed out, with the sky lit up like a bright Christmas tree. Full moons are especially rough on stargazing this time of year because they trace a very high arc across the sky through the course of the night. In fact, they take about the same high arc across the sky as the sun does on the first day of summer.

If you’ve been good this year you may get a new telescope under the Christmas tree, but unless you want to get really frustrated I’d wait until New Year’s before you give it “first light” from the stars. The moon rises much later at night and the early evening skies are a lot darker.

Even though the sun has a much lower profile this time of year it’s about to make its big annual move at 10:48 p.m. Monday. That’s the moment of the winter solstice, the first day of winter and also the moment we start gaining daylight once again.

This time of year you’ve no doubt noticed that the sun takes a very low arc across the southern sky, rising in the southeast and setting in the southwest, and spending less than nine hours above the horizon. Monday is the day that the sun reaches its lowest point in the southern sky. We’re not being delivered nearly the amount of solar power as we get in the summer.

From now through late next June the sun’s arc across the heavens will get higher and higher and we’ll eventually get warmer. However, the coldest weather of the winter is yet to come. That’s because of the north polar regions where there’s been little or no sun since autumn began in September. For some time now and super cold air has had a chance to built up. Because of the Earth’s rotation and general wind circulation patterns the polar cold has to go somewhere. Naturally some of it will spill our way in intervals well into the spring. I call it the polar hangover effect.

Mike Lynch is an amateur astronomer and professional meteorologist.