Winter Officially Begins Today in the Northern Hemisphere

Winter officially arrives in the Northern Hemisphere today at 10:27 p.m. EST. My fifth-grade students often ask me why the start of a new season doesn't begin at midnight on a certain date, much like the beginning of a new year. The answer has to do with the Earth, the tilt on its axis, and its revolution around the Sun.

I've always maintained that the start of a new season is more of an "event" than watching the ball drop in Times Square on New Year's Eve. That's because New Year's Day is a "man-made" holiday which can arbitrarily occur at any time during a calendar year. An equinox or a solstice, however, marks a precise time when the Sun's rays strike a particular point on the face of the Earth. I try to observe the arrival of a new season, and today will be no exception.

As the Earth travels around the Sun in its orbit, the North-South position of the Sun changes over the course of the year due to the changing orientation of the Earth's tilt with respect to the Sun. The dates of maximum tilt of the Earth's equator correspond to the Summer Solstice and Winter Solstice, and the dates of zero tilt correspond to the Vernal Equinox and Autumnal Equinox.

In the Northern Hemisphere, the Winter Solstice is day of the year when the Sun is farthest South. However, in the Southern Hemisphere, the Winter and Summer Solstices are the opposite, so that the Winter Solstice occurs on the first day of Summer in the Northern Hemisphere. The Sun's direct rays will be over the Tropic of Capricorn next Thursday morning.

The Winter Solstice also marks the "shortest day" of the year in terms of daylight. The length of time elapsed between Sunrise and Sunset at the Winter Solstice is at a minimum for the year. Of course, Daylight Saving Time means that the last Sunday in March has 23 hours and the first Sunday in November has 25 hours, but it does not correspond to the actual number of daylight hours.

Finally, the shadows cast by the Sun will be at their longest by the end of this week, since the Sun is at its lowest point in the sky. The actual times of Sunrise and Sunset in southwestern Connecticut for the Solstice are 7:16 a.m. and 4:27 p.m., respectively. Consider that on the first day of Summer in late June, the Sun rises at 5:19 a.m. and sets at 8:30 p.m. So, today's "length of day" is only nine hours and 11 minutes as opposed to 15 hours and 11 minutes exactly a half-year later.

So, as we prepare to welcome Winter, also realize that its arrival marks a turning point. The days will gradually begin to get longer from this point forward until the end of June. Things can only get brighter from here on out.

Paul