When it is noon in Seoul, 89 places are still on yesterday
Pick a city in CouchColumbus and it shows you the current local time there. Coordinates are enough to compute distance, but not time. A time offset is not geography but a rule each country sets, so every city has to carry its own zone. The 524 cities in the dictionary hold 201 distinct zones.
Line those 201 up against Seoul and you get 27 different offsets.
| vs. Seoul | Cities | Such as |
|---|---|---|
| +4 hours | 2 | Apia, Nukuʻalofa |
| +3 hours | 10 | Auckland, Petropavlovsk-Kamchatsky |
| 0 hours | 44 | Tokyo, Fukuoka (including 17 in Korea) |
| −6 hours | 61 | Istanbul, Nairobi |
| −7 hours | 118 | Paris, Rome, Barcelona |
| −13 hours | 29 | New York, Havana |
| −19 hours | 3 | Honolulu, Papeete, Rarotonga |
Twenty-three hours separate the earliest clock from the latest. The 118 crowded into the −7 row is because it is September and continental Europe is on summer time. In winter that pile shifts one row over.
Places where you travel 5,000km and never change the clock
There are 27 foreign cities at zero offset. Twenty-five of them are in Japan; the other two are these.
- Koror (Palau) — 3,445km from Seoul
- Dili (Timor-Leste) — 5,131km from Seoul
Dili is 5,131km from Seoul and requires no change to your watch at all. Meanwhile Dalian, a mere 493km from Seoul, requires an hour. And Bali, 1,142km west of Dili, also requires an hour. Two places a factor of ten apart in distance share the same offset.
Some places use half-hour or quarter-hour steps. There are 26 in the dictionary: 13 in India and 2 in Sri Lanka at UTC+5:30, 2 in Nepal at UTC+5:45, 2 in Myanmar at UTC+6:30, 3 in Iran at UTC+3:30 and 4 in central Australia at UTC+9:30. Kathmandu is 3 hours and 15 minutes from Seoul.
Apia, with the date line in between
Apia has the earliest clock in the dictionary, 4 hours ahead of Seoul. And yet its longitude is 171.8° W, in the middle of the Pacific, 8,568km east of Seoul.
Work out solar noon from longitude alone and you get this.
- Solar noon in Seoul — 03:32 UTC
- Solar noon in Apia — 23:27 UTC
Apia's sun reaches its peak nearly 20 hours later than Seoul's. And yet the calendar is a day ahead of Seoul. Measure that same solar noon on an Apia clock and it reads 12:27 — a thoroughly ordinary midday. What is out of step is not the time but the date.
Samoa moved from the east side of the date line to the west in 2011. It skipped an entire day to do it, so 30 December of that year does not exist in Samoa. There are few better demonstrations that a time offset is not geography but a decision.
Yesterday and tomorrow, depending on the hour in Seoul
Count the dates across all 524 cities against the clock in Seoul and it looks like this.
| When Seoul is at | Places on yesterday | Places on tomorrow |
|---|---|---|
| 8am | 115 | 0 |
| noon | 89 | 0 |
| 8pm | 0 | 2 |
| 11pm | 0 | 26 |
While you eat lunch, 89 places in the dictionary are still on yesterday. Before you go to bed, 26 are already on tomorrow. No city in the dictionary uses UTC+14, so at no moment do the dates spread across three days.
The cities where the clock disagrees most with the sun
A standard time zone is a scheme for binding a wide span of longitude to a single reading. So the clock and the sun fall out of step even within one country. Sort by latest solar noon and western Spain comes up in a row.
| City | Solar noon by the clock |
|---|---|
| Santiago de Compostela (Spain) | 14:34 |
| Nuuk (Greenland) | 14:27 |
| Seville (Spain) | 14:24 |
| Madrid (Spain) | 14:15 |
| Surabaya (Indonesia) — the earliest | 11:29 |
By longitude Spain is in the same band as Britain, and yet it uses Central European Time. Add summer time on top and at noon in summer the sun is still in the east. The other end is Surabaya, where the sun peaks while the clock still reads half past eleven.
What we are not certain about
- Offsets were calculated as of 15 September 2026. There are 210 cities in the dictionary, across 54 countries, whose offset differs between September and January because of summer time. Even among the 84 featured destinations, 29 change with the season.
- Which is why this service does not store an offset per city, only a zone name like
Asia/Seoul. Summer time is left to the browser. Freeze it as a value and it goes wrong twice a year. - Solar noon is mean solar time derived from longitude alone. The real sun runs about ±15 minutes early or late depending on the season.
Build an itinerary and the destination card shows the current time there. That number does not come out of the distance. It is a rule somebody set at some point, and if they decide to change it — as Samoa did — it changes.