World Clock
Track live time, local dates, and day differences across major cities worldwide.
How Time Zones Work Across the World
Standard time zones were created to synchronize human activity with the Earth's 24-hour rotation relative to the Sun. Here is how longitude, political boundaries, and planetary rotation shape world time:
1. Longitude Defines the Core Time Zone
The Earth rotates $360^\circ$ every 24 hours, meaning every $15^\circ$ of longitude roughly corresponds to a 1-hour time difference. Cities located along the same vertical line of longitude (such as London, UK and Accra, Ghana) generally share the same baseline time zone.
2. Multiple Time Zones in Single Countries
Large countries spanning wide horizontal distances use multiple time zones. For example, the United States spans 6 standard time zones, Australia spans 3, and Russia spans 11 time zones from west to east.
3. Solar Sunrise Sequence (East to West)
Even when two cities share the exact same official time zone, the Sun rises earlier in the eastern city than the western city. Because the Earth rotates counterclockwise (west to east), light hits eastern locations first.
4. The International Date Line (1-Day Jump)
Located roughly along the $180^\circ$ meridian in the Pacific Ocean, crossing the International Date Line shifts the date by a full 24 hours. Traveling west adds a day, while traveling east subtracts a day.
5. Fractional & Half-Hour Time Zones
Not all time zones differ by full hours. Countries like India (UTC+5:30), Iran (UTC+3:30), and parts of Australia (UTC+9:30) use half-hour offsets, while Nepal (UTC+5:45) uses a 45-minute offset to match local solar time more accurately.