HAPPY WINTER SOLSTICE

The Winter Solstice occurred today at exactly 5:02 AM (EST). It is important to understand that the two seasonal solstices (winter and summer) and the two seasonal equinoxes (spring and fall) are astronomical events that occur at exact positions (and therefore exact moments in time) during Earth's 365.25 day, 65,000 mph trip (orbit) around the Sun. Today's Winter Solstice is the position at which the northern hemisphere experiences the maximum relative tilt of Earth's rotational axis away from incoming sunlight. This produces three observable effects regarding the amount and intensity of sunlight received: 1) the fewest hours of sunlight (latest sunrise and earliest sunset), 2) the lowest sun angle (height above the horizon) of the year which causes, 3) the weakest, most diffuse (spread out) sunlight. The direct result of the diminished strength and duration of daily sunlight at this time of year is just what one would expect: a generally cold winter season.

The amount and strength of sunlight varies considerably with latitude; the greater the distance from the equator, the shorter the window of sunlight becomes. Here in upstate New York, we'll receive about 8 to 9 hours of sunlight, whereas residents of northern Alaska will see only 2 or 3 hours of light. And Santa way up on the North Pole will never see the Sun! This explains why winters are colder the further north one travels. For the 30% of Earth's population living in the Southern Hemisphere, today is their Summer Solstice (maximum length and strength of sunlight) making Christmas in Australia and Argentina a beach holiday!

The Winter Solstice also marks the "return of light" as the amount of sunlight starts to increase by about two minutes per day beginning tomorrow! This gradual increase in light at sunrise and sunset is usually noticed around late January or early February when someone will remark, "Hey its starting to get light again!" You can always tell them that, "it's been getting lighter since December 22nd!"

In the popular media, the Winter Solstice is deceptively referred to as the "shortest day of the year" suggesting it is less than 24 hours long or the "first day of winter" which mistakenly suggests a connection to the day's weather (It can be unseasonably warm on the Winter Solstice). And interestingly enough its is never called the "weakest day of the year" - but it is! There is no need to apply sun bloc in the winter - not because air temperatures tend to be cold - but because incoming UV light is the weakest (most diffuse) resulting in a low UV index even if it's a bright and sunny day.

Holidays lights are no coincidence at this time of year as agrarian societies celebrated the "return of sunlight", the essential ingredient for a new growing (farming) season. And so the Winter Solstice marks a time of hope and renewal that is celebrated all over the Northern Hemisphere in late December.