1. Aim: How are time zones created?

2. Objectives
Understand the relationship between longitude, rotation and time.
Calculate local time when given GMT
Calculate longitude when given GMT

4. 1. How are time zones created?
Earth is divided into 24 time zones based on longitude.
Each zone is about 15o of longitude = 1 hour
The Earth rotates 150/hour
And also in here

5. The time zones are not perfect.

6. Ex 1: 6 am in Denver = ________ in San Francisco?
As you travel WEST, time goes ______________ (subtract)
As you travel EAST, time goes _____________ (add)

9. Ex 2: 4 pm at A = __________ at B?

10. Ex 3: If you could instantly travel 45o west from NYC, what would be the time difference?

11. 2. What is solar noon?
12:00 pm is known as solar noon or local solar noon, or the time of day when the sun reaches its highest point in the sky.
Locations with the same longitude have the same solar noon, because the sun hits its highest point in the sky all along that line of longitude at the same moment.

12. 3. What is Greenwich Mean Time (GMT)?
The prime meridian passes through Greenwich, England.
Your longitude can be calculated by comparing local time with GMT.
Your longitude = difference from GMT x 15o/hour

13. Ex. 4: What time is it in Greenwich, England (at 0° longitude), when it is noon in Massena, New York?

14. Example 5: Your local solar noon occurs at 8 AM Greenwich time
Example 5: Your local solar noon occurs at 8 AM Greenwich time. What is your longitude?

15. Example 6: Your longitude is 150oW and the time is 6:40 AM
Example 6: Your longitude is 150oW and the time is 6:40 AM. What time is it in London, England?

16. 4. What happens when we cross the International Date Line?
September 1, 2010
September 2, 2010

17. 5. Time Math
Example: (hh:mm:ss) Remember: You must “borrow” or take 60 minutes or 60 seconds 11: 15 : : 23 : : 52 : 28