Time Zones
Aim: How are time zones created?
Objectives
• Understand the relationship between longitude,
rotation and time.
• Calculate local time when given GMT
• Calculate longitude when given GMT
• http://www.youtube.com/watch?v=hSGeSRdztzM&feature=re
lated
• http://video.google.com/videoplay?docid=5041127474937930014#
• http://www.time.gov/
• http://www.usflashmap.com/products/time_zone_map/actions
cript-time-zone-map.htm
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
The time zones are not perfect.
http://www.timezonecheck.com/
Ex 1: 6 am in Denver = ________ in San
Francisco?
• As you travel
WEST, time goes
______________
(subtract)
• As you travel
EAST, time goes
_____________
(add)
Ex 2: 4 pm at A = __________ at B?
Ex 3: If you could instantly travel 45o west from
NYC, what would be the time difference?
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.
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
Ex. 4: What time is it in Greenwich, England
(at 0° longitude), when it is noon in Massena,
New York?
Example 5: Your local solar noon occurs at 8
AM Greenwich time. What is your longitude?
Example 6: Your longitude is 150oW and the
time is 6:40 AM. What time is it in London,
England?
4. What happens when we cross the
International Date Line?
September 1, 2010
September 2, 2010
5. Time Math
• Example: (hh:mm:ss)
Remember: You must “borrow” or take
60 minutes or 60 seconds
11: 15 : 32
-07: 23 : 04
3: 52 : 28