Winter’s start and the shortest day sometimes differ

From Dec. 8, 2017:

Our current calendar is fairly accurate in that it takes the Earth 3651⁄4 days to travel around the sun every year. With that in mind, how come the winter solstice isn’t on the same day every year?

The winter solstice can occur on Dec. 20, 21, 22 or 23. The last Dec. 23 solstice was in 1903 and will not happen again until 2303.

There’s a difference between the tropical year (the time the sun takes to return to the same position in the seasons cycle) and the calendar year.

The tropical year is approximately 365.242199 days, but it varies from year to year because of the influence of other planets and the wobble in the Earth’s axis. Over time, that means the dates of the solstice are going to vary.

Winter solstice is the shortest day of the year in terms of daylight, but it does not have the latest sunrise nor the earliest sunset of the year. That’s because of the equation of time, the difference between how we keep times with our watches and how time is measured using the sun.

They are not always the same thing. If you were to check the sunrise and the sunset times for any city in the Northern Hemisphere around the December solstice, you would see the earliest sunset occurs a few days before the solstice and the latest sunrise happens a few days after the solstice.

This has to do with sun’s declination, the angle at which the rays of the sun hit the plane of Earth’s equator.

I could go into all the numbers and dates, but, trust me, that all gets really boring and confusing.

Winter also means it’s time for The Republic’s Season for Sharing campaign, a cause long near to Clay’s heart.

You can donate in his memory and help stop goobers (people who know help is needed, who can help, but don’t) by going to sharing.azcentral.com, facebook. com/seasonforsharing, or by clipping the coupon on Page 4A of today’s newspaper.

Be sure to mention goobers.