[tz] Yet more historical data for Iran

Roozbeh Pournader roozbeh at unicode.org
Wed Jun 1 09:47:13 UTC 2022

Yet another discovery, which clarifies what happened in 1977 and 1978 in

This is from Kayhan newspaper, one of the major Iranian newspapers, from
March 20, 1978, page 2:

"Pull the clocks 60 minutes forward

As we informed before, from the fourth day of the month Farvardin of the
new year [=1978-03-24], clocks will be pulled forward, and people's daily
work and life program will start one hour earlier than the current program.

On the 1st day of the month Farvardin of this year [=1977-03-21], they had
pulled the clocks forward by one hour, but in the month of Mehr
[=1977-09-23], the clocks were pulled back by 30 minutes.

In this way, from the 4th day of the month Farvardin, clocks will be ahead
of the previous years by one hour and a half.

According to the new program, during the night of 4th of Farvardin, when
the midnight, meaning 24 o'clock is announced, the hands of the clock must
be pulled forward by one hour and thus consider midnight 1 o'clock in the

This implies that in September 1977, when the daylight savings time was
done with, Iran didn't go back to +03:30, but immediately to +04:00.

I'm still trying to figure out when exactly did Iran go back from +4:00 to
+03:30. I'll report back when I find it. Based on the time of true noon
announced in newspapers of the time, I've triangulated it to some time
between 1978-11-05 and 1979-01-15, but it looks like major Iranian
newspapers were stopped from publishing during most of that time period, so
I can't figure out more using this method.

For now, two changes are needed in tzdata, first is the start of daylight
saving in 1978, the other the switch to +4:00/+5:00, which is currently
listed as Nov 1977, but should change to exactly the end of daylight saving
time in 1977.

Thanks again,
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