1. ©G Dear 2009 – Not to be sold/Free to use
General Mathematics
HSC
Spherical
Geometry
Time Zones
Stage 6 - Year 12
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©G Dear 2009 – Not to be sold/Free to use

2. Time zones are calculated in relation to GMT. Greenwich Mean Time
For locations to our east we add time.
Sydney =
Adelaide + 30min
= 9am + 30min
= 9:30 am
Adelaide
9am
Sydney
9:30am
Map

3. Time zones are calculated in relation to GMT. Greenwich Mean Time
For locations to our east we add time.
For locations to our west we subtract time.
Perth =
Adelaide – 1hr 30min
= 9am - 1hr 30min
= 7:30 am
Perth
Adelaide
9am
7:30am
Map

4. Time Zone (2/9) If it is 7:08am [07:08 hrs] hours in London …
… what time is
it in Sydney?
Sydney =
London + 10hr [East]
= 07: hr
= 17:08
= 5:08 pm
Map

5. Time Zone (3/9) If it is 10:20am [10:20 hrs] hours in Sydney …
… what time is
it in Honolulu?
Honolulu =
Sydney - 20hr [West]
= 10: hr
= -10:20
+ 24:00
= 14:20 yesterday
= 2:20 pm yesterday
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6. = 10:20 + 4 hr [Crossing ‘Date Line’ subtract one day] = 14:20
Time Zone (4/9)
If it is 10:20am
[10:20 hrs]
hours in Sydney …
… what time is
it in Honolulu?
Honolulu =
Sydney + hr [East]
= 10: hr [Crossing ‘Date Line’
subtract one day]
= 14:20
= 2:20 pm yesterday
Map

7. When crossing the International Date Line…
Time Zone (5/9)
When crossing the International Date Line…
going east – subtract one day
going west – add one day
When determining time zones
1o in longitude equals 4 minutes.
15o in longitude equals 1 hour.
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8. USA Time Zones (6/9) Time Zone = -75 x 4 mins = -300 mins = -5 hrs
75oW
Time Zone
= -75 x 4 mins
= -300 mins
= -5 hrs
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9. USA Time Zones (7/9) Time Zone = -90 x 4 mins = -360 mins = -6 hrs
90oW
75oW
Time Zone -5
= -90 x 4 mins
= -360 mins
= -6 hrs
Map

10. USA Time Zones (8/9) Time Zone = -105 x 4 min = -420 mins = -7 hrs
105oW
90oW
75oW
Time Zone -6 -5
= -105 x 4 min
= -420 mins
= -7 hrs
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11. USA Time Zones (9/9) Time Zone = -120 x 4 min = -480 mins = -8 hrs
120oW
105oW
90oW
75oW
Time Zone -8 -7 -6 -5
= -120 x 4 min
= -480 mins
= -8 hrs
Map