Can a country change its offset without changing longitude?

Yes. That is the usual case. Longitude did not move when Turkey stayed on UTC+03:00.

Why keep historical zones?

Legal, aviation, and log reconstruction. tzdb is a history of civil time, not only a now() function.

Where should I read more on this site?

The IANA database guide, the China one-zone article, and the half-hour offsets article. City notes call out national quirks in one paragraph each.

Why time zone offsets are political

If Earth were divided into 24 equal bands, civil time would be a trigonometry exercise. Instead, Spain sits on UTC+01:00 despite a Greenwich-ish longitude, China uses one clock, and Samoa jumped the date line for trade.

Last updated 2026-08-20 · Written by the NowZones publisher in Denmark. Offsets and DST examples use the IANA Time Zone Database via the same libraries as the city clocks. This is editorial explanation, not legal, medical, or aviation advice.

Geography is only the sketch

Fifteen degrees of longitude is roughly one hour of Earth rotation. Idealised zones follow that sketch from the Greenwich meridian. Real zones follow railways, empires, and television markets.

France and Spain using Central European Time means western Spain runs civil clocks far ahead of the sun. Western China does the same on UTC+08:00. Those are energy and nation-state choices, not mistakes in IANA.

Fractional offsets (India +05:30, Iran +03:30, Nepal +05:45) are also political settlements. They are why “round hours only” UIs fail.

Offsets that moved

Spain switched toward CET during the Franco period and stayed. Russia has swung between permanent DST and standard time; Moscow is now UTC+03:00 year-round. Chile and Turkey have turned DST on and off in living memory.

IANA tzdb’s job is to record those moves so 1995 timestamps still convert. A world clock that only ships “current offset” will mis-convert old logs. NowZones pages show the current civil clock and the next transition, not a full history table — the tz database remains the history.

When a legislature acts, packagers ship a tzdata update. Phones that never update stay wrong. That is an operations problem, not a search-engine problem.

What a city page should admit

We name the IANA id so you can see the political object, not just “GMT+8.” China Standard Time is a national policy; Asia/Shanghai is how software spells it for the cities we publish.

Country hubs for China, India, and the US exist because those policies are the story: one clock, one half-hour clock, and many clocks. Read those hubs before you assume a country has a single time.

Try the tools

Frequently asked questions

Can a country change its offset without changing longitude?: Yes. That is the usual case. Longitude did not move when Turkey stayed on UTC+03:00.
Why keep historical zones?: Legal, aviation, and log reconstruction. tzdb is a history of civil time, not only a now() function.
Where should I read more on this site?: The IANA database guide, the China one-zone article, and the half-hour offsets article. City notes call out national quirks in one paragraph each.