As a cold winter storm moves through the region, snow showers will decrease in both the valleys and the mountains Saturday, leaving behind a cold and dry Christmas Day. Scattered snow showers will pop up Saturday during the day, with minor valley accumulations possible and an additional couple of inches in the mountains during the daylight hours. Saturday and Sunday’s high temperatures will barely break the freezing mark, with overnight lows dropping into the teens Sunday and Monday morning. For the rest of the next week, a dry and slowly warming trend will settle in.

winter-solstice

Yesterday I wrote that while the day of the Winter Solstice (Dec 21 this time around) is the shortest day of the year, it doesn’t have the latest sunrise or the earliest sunset (those are January 4 and December 6 respectively.) Why is that? It’s a little tough to visualize, but the short answer is that it has to do with the fact that our orbit around the sun isn’t a circle, but rather elliptical, and the earth’s elliptical orbit causes us to change speed during our yearly trip around the sun…going faster when we are closer to the sun (perigee) and slower when we are the farthest out (apogee.) .

elliptical

This time of year, we are near perigee, the closest to the sun, and are travelling “fast.” On any average day we travel about a degree around the sun, since there are 360 degrees in a circle and 365 days in a year. When we are moving faster, we travel a little more than average around the sun, and when we travel slower, we travel a little less. Since we measure our day with respect to the sun, that change in speed throughout the year means that we have to spin a little further in the winter to make up for the extra angle top the sun that we have traveled, which makes the latest sunrise happen a little later in the year than it would if the speed was constant, and the earliest sunset happens earlier in the year.

bethlehemchristmascitystar

And just a quick note to wish you all a very Merry Christmas, filled with all the joy present that first Christmas morn.

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