Time Zones and the International Date Line
Earth is divided into 24 time zones that shift by one hour per 15° of longitude.
About this topic
Earth rotates 360 degrees every 24 hours, so 15 degrees of longitude equals one hour of time. Standard time zones are based on this, set relative to Coordinated Universal Time (UTC) from the Prime Meridian; countries adjust boundaries for convenience (China uses a single zone across a vast width, while Russia spans eleven). Time zones solved the problem of local sun time differing from town to town once railways arrived and timetables needed consistency.
Worked example: if it is 12:00 noon in London (0 degrees) then at 75 degrees W (New York) the sun is behind by 75 / 15 = 5 hours, so it is 07:00; at 150 degrees E (Sydney area) it is 10 hours ahead, so 22:00. Remember that places to the east are ahead and places to the west are behind, because the sun rises in the east first.
The International Date Line, roughly at 180 degrees longitude, is where the calendar date changes: crossing it westward adds a day, eastward subtracts one. It zigzags to avoid splitting countries and island groups. Daylight saving time moves clocks forward in summer to make better use of evening light. A common error is to think the date line is the same as the Prime Meridian; they sit on opposite sides of the globe. Time zones matter for flights, global business, broadcasting and internet meetings.
Key ideas
- Prime Meridian runs through Greenwich
- Date line at 180°
- Cross it going east and the date goes back a day
Quick check
Use cases: where Time Zones and the International Date Line helps
- Homework: review the key idea behind Time Zones and the International Date Line before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Time Zones and the International Date Line without notes.
- Visual learning: play with the interactive lab to see how Time Zones and the International Date Line changes when you adjust its inputs.
- Teaching a friend: explain Time Zones and the International Date Line in your own words, then compare your version with the key ideas.
Geography helps with city planning, climate, trade and migration.
Frequently asked questions
What is Time Zones and the International Date Line?
Earth is divided into 24 time zones that shift by one hour per 15° of longitude.
What will I learn in Time Zones and the International Date Line?
Prime Meridian runs through Greenwich. Date line at 180°. Cross it going east and the date goes back a day.
Is Time Zones and the International Date Line part of Geography?
Yes. It is one of 40 Geography topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Time Zones and the International Date Line lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Time Zones and the International Date Line?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.