Earth's time zones – the International Date Line and day length
GeographyEarth in SpaceAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Earth in Space
A hand-drawn world map splits into 24 time zones (15° of longitude each), with the 0° prime meridian and the 180° International Date Line marked. Drag the Sun across the map or press Run to let time pass: the night region shifts and the time and date of several cities (London, Bangkok, Tokyo, New York, Sydney, Moscow) update live. Drag the observer point anywhere to read off its time zone, local time, sunrise and sunset, and day length for that latitude and day of the year.
Lesson: Geographic consequences of Earth's motions: time zones, the International Date Line, and day length across seasons and latitudes
What it shows
Earth turns 360° in 24 hours, so local solar time changes by 4 minutes for every degree of longitude, or one hour for every 15°. To simplify timekeeping, the world is divided into 24 standard time zones, each using the time of its central meridian, counted from GMT at the prime meridian. Opposite the prime meridian, the International Date Line at 180° marks where the calendar date changes. Day length depends on latitude and on the Sun's declination through the year: it stays close to 12 hours at the Equator, while high latitudes have continuous day or night around the solstices.
How to use
Set the Starting GMT time and the Day of year, then press Run and watch the night shading sweep westward across the time zones while the city clocks update. Drag the red observer dot, or change Observer longitude, to compare local solar time with zone time. Move the observer across the 180° line to see the date change. Then vary Observer latitude and the day of the year to compare sunrise, sunset and day length.
Parameters you can change
- Observer longitude (negative = West) -180–180 °
- Observer latitude (negative = South) -85–85 °
- Day of year (1 = Jan 1) 1–365 day
- Starting GMT time 0–23.5 hour
- Shade the night region
Questions to explore
- When it is 05:00 GMT, what is the zone time at longitude 135° E?
- A ship crosses the 180° meridian travelling from west to east. How must the date on board change, and why?
- On day 172 (21 June), how does day length at latitude 50° N compare with latitude 50° S?
