Governments require us to change our clocks by one hour, from standard time to “daylight saving time,” between a date in spring and a date in autumn. The mnemonic is: “Spring forward, Fall back.”
USA: March 2nd Sunday, November first Sunday
2024 March 10, November 3
2025 March 9, November 2
2026 March 8, November 1
2027 March 14, November 7
2028 March 12, November 5
2029 March 11, November 4
2030 March 10, November 3
Europe: March last Sunday, October last Sunday
2024 March 31, October 27
2025 March 30, October 26
2026 March 29, October 25
2027 March 28, October 31
2028 March 26, October 29
2029 March 25, October 28
2030 March 31, October 27
That is a first approximation. About 300 countries and territories have their own rules.
This graph shows sunrise and sunset times for latitudes 30°, 40°, and 50° north, approximating the contiguous USA, which spans from 24° to 49°. The vertical blue lines are the hours of actual time. The orange lines show the clock times, as displaced in the summer months for the USA, with 12 noon and 12 midnight emphasized. The shift-kinks, as we could call then, are for 2020; for other years they will be at different dates.
The steps from natural time to artificial time
The natural time by which we live on our rotating planet is determined by the Sun. Twelve noon is when the Sun is highest, on the meridian or midline of the daytime sky. Everything else follows from that.
This apparent, or observed, time is not quite regular, because days vary slightly in length (due to the Earth’s orbit and tilt). The Sun arrives slightly early or late at the noon meridian. By subtracting the “equation of time” from this apparent time we get mean time, regular throughout the year. So this is a first step away from truly natural time, but it is a simplification.
Next is the step from mean time to standard time, by which clocks are set. Places within a time zone, a north-south strip of Earth from pole to pole, all use the time of its standard meridian of longitude (ideally, its central meridian), instead of their own slightly differing natural times. Since we divide the day into 24 hours, the strips are (ideally) 15 degrees of longitude wide. Clocks toward the western and eastern edges of a zone say noon about half an hour before and after the Sun has really reached its noon position.
This system is still fairly simple and fairly near to natural time. The next step of complication is that the boundaries of the time zones do not keep strictly to lines of longitude. Most of them follow, on land, the boundaries between political units. So they are quite jagged, and sometimes displaced an hour or more east or west.
For instance, longitude 0 runs through the British Isles, but the only other European country keeping to that time zone is Portugal; all the other western and central European countries unite in a kind of general European zone stretching from about longitude 9° west to 20° east, with clocks one hour later.
The step too far
On top of these unavoidable shifts from natural time to standard time, there has been imposed a complication which yanks us a whole hour away, for much more than half of the year. This is the so-called Daylight Saving Time.
Since no time or daylight is “saved,” George Lovi suggested the term Daylight Displacement Time. It could also be called Daylight Shifting Time, or Clock Twisting Time.
In North America, or most parts of it, the rule is that clocks must be turned an hour forward at the beginning of the second Sunday in March, and an hour backward at the beginning of the first Sunday in November. Other countries have other rules, but we can use the North American example for discussion.
The purpose is to make everyone get up an hour earlier during the summer months, when the Sun is rising earlier. You sharply start getting up an hour earlier, because the Sun is gradually rising earlier. All summer, it is as if you are displaced one time-zone to the east. Real 8 is called “9,” and so on with every other hour. The Sun is highest not at 12 noon by the clock but at 1.
Exact instant
The clock change is supposed to be made. by everyone simultaneously, in the small hours of Sunday, presumably because not much else is then being done. In Europe, the specified instant is 1 Universal Time, irrespective of what time zone you are in. For America, it is 2 A.M. – Eastern Time! So, theoretically, you should figure out what clock time, of which kind, this translates to in your zone of either continent.
The instant is specified for the harmony of machines, which can be programmed to wait for it. People, except the most grimly rule-abiding, will just twist their clocks before bed on Saturday; or, forget to do it for a day or two.
In official American time, the hour between 2 and 3 A.M. does not exist; that March day is only 23 hours long. In November, the hour between 1 and 2 A.M. is repeated; the day is 25 hours long.
Geographical differences
Clock shifting has been tried in most of the world’s countries: that is, all except some that are at low latitudes (where the length of the day scarcely varies): the Guianas, west and central Africa, Arabia, Afghanistan, southeast Asia, Indonesia.
But more than half of the world has, after trying it, abandoned it: all of South America except Chile and Paraguay, all of Asia except Israel, Lebanon, Syria, and Iran, all of Australia except its three southeastern states.
A listing of the variety of past and present practices would be longer than the number of the world’s countries, because many sub-regions have their own rules amd histories.
The change is not made in American Samoa; Guam; the Northern Marianas; Hawaii; Arizona except the Navajo reservation; Puerto Rico; the Virgin Islands.
Canada keeps in step with corresponding zones in the USA., but several scattered regions do not make the change, and a few keep the changed time all year. Mexico similarly tries to keep in step with the USA, making the change except in its state that is south of Arizona.
In Europe (except Iceland, Belarus, and Russia) the change to “Summer Time” is made for a shorter part of the year than in America
History
Benjamin Franklin did not propose clock-changing in his letter published anonymously in Paris in 1784; he suggested actions, such as firing a cannon, to make people get up at sunrise. A much better idea!
Clock-changing was proposed by George Hudson, a New Zealand entomologist, in 1895, and by William Willett in England in 1905. Versions of it first became law in a Canadian town in 1911, then by countries on both sides of the First World War: Britain, Germany, and Austro-Hungary in 1916, Russia in 1917, the United States in 1918. It was abandoned except in Canada, then gradually brought back to many countries.
In the USA from 1966 to 1986 (with wild variations 1974-76) clocks were changed on
April last Sunday and October last Sunday.
In 1986 the rule changed again, to
April 1st Sunday and October last Sunday.
In 2007 (by the “Energy Policy Act of 2005”) yet again, to
March 2nd Sunday and November 1st Sunday.
This puts 65% of the year on the dislocated time in which “12 midnight” and “12 noon” are an hour before the middles of the night and day.
At the Greenwich Observatory itself, there is a large collection of historic clocks, many of them with loud chimes and elaborate mechanisms. Changing them all by an hour twice a year would be a huge task. So – most of them are left on standard Greenwich Mean time
Non-fit to the Sun
What is “time”? That’s a deep mystery, but “time of year” and “time of day” are concrete; they reduce to place. Time of year, as when we talk about summer or about October, is determined by Earth’s position in its orbit around the Sun. Time of day, as when we talk about night or about ten o’clock, is equivalent to our position, in relation to the Sun, on our rotating planet. If time of day for you is twelve noon, that means your location is facing toward the Sun.
Or did. Now “12 noon” is applied, much of the year, to a moment when the Sun is still an hour away from reaching the meridian. This is a falsehood, or at least a misnomer.
The misnomer is an inconvenience that plagues those trying to make astronomical calculations, or trying to describe astronomical events. For instance I can’t say that “Mars rises about 9 P.M. at the beginning of March, 7 P.M. at the end” (making clear that the rising of Mars is shifting at a certain speed, two hours in the month) without having to explain contortedly that by “7” I mean what is now being called 6 by the clock.
It’s an inconvenience that causes a lot of cursing in the restricted field of astronomy, but I think it is more than that. There is deeper harm to education. Part of the mental equipment we acquire as we grow up is knowledge of what “south” means and roughly where it is; a related part is knowing that day is from sunrise to sunset, “noon” or “midday” is the middle of it, and is when the Sun is highest and is in the south. If we can’t pass on this clear picture to children, a curtain closes between mind and nature.
Non-fit to latitude
“Daylight saving time” tries to approximate the smooth change of the seasons by a sudden one-hour chop. It is hopelessly insensitive to latitude, except that it is just ignored in countries nearer to the equator.
At latitudes around 30°, such as the southern USA, the range between winter and summer sunrise times (or sunset) is 2 hours or less. At around 40°, such as Washington and New York, it is 3 hours. At around 50°, such as London, it is 4 hours. At around 60°, such as Scotland and Norway, it is 6 hours or more.
So, not even for the southern USA does a sudden clock-change of one hour much improve the fit between clock time and daylight.
Making it even worse
Almost every year, politicians or others propose that we cease the twice-a-year clock changing ordeal – but in precisely the wrong way: keep the whole year on the displaced time! This would cancel any supposed benefit of pushing 8 o’clock back to 7 for part of the year, but no benefit would be achieved – only the gross and educationally confusing misfit to natural sun time.
Medical professionals overwhelmingly recommend permanent standard time (as reported in a 2023 Journal of the American Medical Association article). They say our circadian clocks are out of step with daylight throughout the clock-shifted months, increasing poor sleep, vehicle crashes, depression, and stroke.
The U.S. tried the change to permanent shifted time is in 1974. It rapidly became so unpopular that it had to be undone. Russia tried it in 2011 and abandoned it in 2014.
Other difficulties
Elaborate documents are needed to help people with the tangled proroblems related to clock-changing, such as
https://www.nist.gov/pml/time-and-frequency-division/popular-links/daylight-saving-time-dst
I have heard from people who have to change as many as thirty clocks in their houses or offices; or who refuse to clock-change and instead adopt various strategies for organizing their schedules by standard time.
Changing habits instead of clocks
Clock-changing arose because people now live by rules such as “Report for work at 9” rather than “Get up at sunrise.” Better than ordering everyone to twist their clocks would be to introduce changes in the clock times for our activities. This would be sensitive to latitude.
A modern approximation to the old human habit of starting daily life around dawn would be for regions to set opening hours (in standard time) for schools.
In the USA, schools generally open at 8. They could change to 7 for the summer – in Standard Time. The change could be made at, say, the Mondays nearest to the spring and fall equinoxes.
In this version of the graph, clock times stick with standard time, and the orange line represents a suggested clock time for school opening. Similar graphs for other countries could make clear the times that would work for them.
The graph at first glance is scarcely different from the graph of clock-shifting time. The practical effect is essentially the same. The difference is that it is not clocks that are changed from Standard to twisted time: it is habits that are changed from 8 to 7 in Standard time.
Many other activities are keyed to, or are similar to, school opning times.
These adapting-to-the-season actions would still be merely twice a year. They would help to keep children, and all of us, in touch with the natural cycle of the year.
It would be easier to explain to children that school will start an hour earlier because sunrise is getting earlier. “It’s spring, so we’ll start the day earlier” is more intuitive than “We’re gonna have to change our clocks an hour backward – or is it forward? – at some time on the fifth Sunday in March – or is the first in April? . . .”
We already have to remember opening times that vary by shop, restaurant, office, and season.
