Clock Change and Sun Set Time

In spring the clocks jump forward and an hour is deleted. If the change happens at 2am, then 2am never occurs: the minute after 01:59 is 03:00, and that night is 23 hours long.

In autumn the clocks go back and an hour happens twice. The same hour is lived through once on summer time and once on standard time, which is why timetables, alarms and anything paid by the hour need to say which of the two they mean.

Nobody gains or loses sleep over a year. The evening light is simply moved around, and the argument has always been about whether that is worth the disruption.

They are not the same date and never have been. The European Union and the United Kingdom change on the last Sunday in March and the last Sunday in October, everywhere at the same instant — 01:00 UTC — so the local time on the clock differs by country.

The United States and Canada change on the second Sunday in March and the first Sunday in November, at 2am local time, which means each time zone changes an hour after its neighbour.

The result is two ragged periods each year. For about three weeks in March, America is on summer time and Europe is not, so London is four hours ahead of New York instead of five. For a week at the end of October the gap goes the other way. Every recurring international call in the world lands in the wrong hour twice a year because of it.

Most of the world's population does not change at all. China, India, Japan, almost all of Africa and almost all of South-East Asia have no summer time. Countries near the equator gain nothing from it: the day length barely moves.

Others stopped recently. Russia settled on one fixed time in 2014. Turkey did the same in 2016. Brazil abandoned it in 2019. Mexico dropped it for most of the country in 2022, as did Iran.

Inside countries that do change, there are holdouts. Arizona and Hawaii do not move, although the Navajo Nation within Arizona does. In Australia, Queensland, Western Australia and the Northern Territory stay put while the south-east changes.

Both sides of the argument want to stop changing, and they want to stop on opposite settings.

Permanent summer time keeps the light in the evening and puts winter sunrise very late — after 9am in the north of Britain, which is the reason an experiment in the late 1960s was abandoned. Permanent standard time gives earlier sunrises and dark afternoons, and is what most sleep researchers recommend, on the grounds that the body clock is set by morning light.

The European Parliament voted in 2019 to abolish the change altogether. It never happened: member states could not agree which setting to keep, and a continent where neighbours pick differently is worse than the problem. In the United States a bill for permanent summer time passed the Senate in 2022 and then stalled.

Because that is when the fewest people notice. At 1am or 2am on a Sunday almost nobody is at work, very few trains are running, and the date does not change — moving the clock back at midnight would flip the calendar to the previous day, which is a far worse problem for anything that stores a date.

Not everyone picked the same hour. The EU moves at 01:00 UTC, the United States at 2am local, and a handful of countries do it at 3am or at midnight. Lord Howe Island in Australia moves by only half an hour.

South of the equator the seasons are reversed, so summer time runs from about October to April. New South Wales, Victoria, South Australia and Tasmania start in early October and finish in early April. New Zealand runs late September to early April. Chile and Paraguay have their own dates again.

For roughly a month either side, the northern and southern changes overlap and the offset between, say, London and Sydney moves twice in five weeks — first by an hour, then by another.

And a few places are not on a whole hour at all. India is half an hour off, Nepal is three quarters, Newfoundland is half, and the Chatham Islands sit 45 minutes ahead of New Zealand and change with it.