We can change when the sun rises and sets


October 2017

For years, as a party trick, I have asked people which city has more daylight over the course of the year, clouds aside, Miami or Boston. Very few get it, but the correct answer is that they both have the same amount of daylight.

In fact, every place on earth has the same amount of daylight over the course of a year. As the earth rotates while orbiting the sun, all parts face the sun about half the time. So, at the equator, every day is about 12 hours long, all year.

We would all have the same length of day year round as the equator, except the earth is tilted 23.5 degrees relative to the sun. This changes the distribution of the daylight and gives us seasons. It is summer when our part of the earth is tilted towards the sun, and winter when it is tilted away from the sun.

The farther away from the equator you get, the longer the days are in summer and the shorter they are in winter. In fact, when you get to the North and South Poles, there is no daylight in winter; but the days are 24 hours long in summer.

Cape Cod, where I live, is almost half-way between the equator and the North Pole, so our days range from 9 hours and 9 minutes on December 21, to 15 hours and 12 minutes on June 21st. That’s more than a 6-hour difference from the shortest day to the longest day. (Type “Daylight calculator” into a search engine and you can get a list of sites that will give you these figures for anyplace on earth.)

There is nothing we can do about our total daylight and its distribution. But we do have control over the time. Because we are at the eastern end of our time zone, the sun rises at 7:05am on December 21 and sets at 4:14pm. At roughly the same latitude at the other end of the same time zone, Ohio, the sun rises and sets about 45 minutes later (7:49am and 5pm). All of this difference is accounted for by relative location in the time zone.

The current recommendation of an 11-member commission is that Massachusetts join the Atlantic Time Zone with Bermuda, Puerto Rico, the Virgin Islands and parts of Canada. We would use standard time all year. (No more re-setting clocks twice a year). In summer we would have the same hours we have now on Eastern Daylight Time, but in winter our sun would rise and set an hour later than it does now.

I am all in favor of this change but I agree with the condition set by the commission. As the Wall Street Journal put it: “There’s a major caveat for the effort: the commission’s report recommends against Massachusetts making a unilateral move without most of New England. Commission member Paul Frost, a Republican state representative, believes New York would also have to change zones. Otherwise he fears disruptions to financial markets, television-broadcast schedules and travelers.”

OK, there’s time for one more fun test. Two days a year, every place on earth has the same length of day, 12 hours, because the earth is perpendicular to the sun. What are those days? March 21 and September 21. Check it out. YouTube has some good videos of the earth rotating around the sun.

Please follow and like us:

Leave a Reply