Wikipedia:Reference desk/Archives/Mathematics/2018 January 6

= January 6 =

Daylight Savings Maximum Shift In Time
Dear Wikipedia volunteer,

I have already looked at many Wikipedia and Google searched articles on daylight savings. Here in New Zealand we shift our time by 1 hour twice a year for daylight savings. Is one hour standard world wide? I think I recall a state in Australia being 15 minutes shifted. I need to know the maximum shift by any country. Thank you :)

Gedium (talk) 02:48, 6 January 2018 (UTC)


 * First a linguistic point: there is only one S in "daylight saving" (the phrase "daylight-saving time" follows the same pattern as "cost-saving suggestion").


 * Next a standardization point: time zones and daylight-saving time practices depend entirely on local laws in each country or its subdivisions. There are no official world-wide standards, just common practices.


 * Now the answer: the tz database is a compilation of information about time zones and daylight-saving time practices throughout the world from a time several decades ago up to the present. Searching through its data tables, I find that a number of places have used a 2-hour shift temporarily in the past (most of them during World War II; the most recent case was Newfoundland in 1988), but they all stopped doing that. Today the only place shown with a 2-hour shift is Troll (research station) in Antarctica, which, presumably at the decision of the people who work there,switches between UTC and +2.


 * Similarly, the database lists a number of places that have used a shift of less than an hour temporarily in the past&mdash;specifically, 20, 30, and 40 minutes. But, again, there is only one place like that today: the Australian possession of Lord Howe Island, which shifts by 30 minutes. --76.69.117.217 (talk) 03:58, 6 January 2018 (UTC)


 * Perhaps it doesn't need to be said, but many places don't have DST at all, which I suppose would count as a 0-hour shift. Once on Car Talk there was a tongue in cheek proposal for what they called "double-dog DST"; it wasn't adopted anywhere though afaik. --RDBury (talk) 07:05, 6 January 2018 (UTC)


 * Some places, of course, have DST all year round.  Even some of these may advance their clocks in the summer.   The time in Vigo, Spain is identical to the time in Kirkenes, Norway, although the longitude difference is 40°.   As noted here

"Except on the very longest days of summer, the sun never rises before 7 a.m. in the western region of Galicia; in the winter it doesn't rise until 9 -- 20 minutes later than in Copenhagen."