Time zones Introduction

Year 8 MathematicsECHO

All time is measured from Greenwich a suburb of London in England.

The zero degree longitude line or the Prime Meridian passes through Greenwich.

Greenwich Mean Time (GMT) is the time it is in Greenwich.

Greenwich was chosen as a lot of the world’s sea charts were being drawn up in England at that time.

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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.

PerthAdelaide9am

Perth =Adelaide – 1hr 30min= 9am - 1hr 30min= 7:30 am

7:30am

DURING DAYLIGHT SAVING TIMES IN AUSTRALIA, TIMES CHANGE SLIGHTLY

Note: Times are still calculated in relation to GMT times.

North Pole

Line

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Lon

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15°

1 revolution of Earth = 365.25 days 6 hours x 4 years = Leap year & we catch up

1 rotation of Earth = 24 hours

Circle = 360°

360° /24 = 15° = 1 hour

Earth rotates 15° each hour

At the equator Earth ≈ 24,900 miles = 1037.5 miles in an hour

UTC = GMT UTC = Coordinated Universal Time

11.23am Gold Coast Time

Los Angeles is 18 hours behind GoldCoast and is still the day before.

By this photo, you can see more of the world is now into the next day of the calendar. You can see that it has just passed midnight in Bolivia. i.e. 14.33pm – 14hrs = 0033hrs

New York is 15 hours before G.C. Time

i.e. 1433-15=-1 =0033 -1 = 2333hrs

Los Angeles is 18 hours before G.C. Time14.33-18 = 12-4 = 8.33pm

1803 Gold Coast Time – GMT +10

You can see here, that it is about 10pm in Queensland. In this hour, the whole Earth is on the same day. Once it hits 11pm, (Qld time), 15 degrees west of the International dateline is in the next day.

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If it is 7:08am [07:08 hrs]hours in London …

… what time isit in Sydney?

Sydney =London + 10hr [East]= 07:08 + 10hr= 17:08= 5:08 pm

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If it is 10:20am [10:20 hrs]hours in Sydney …

… what time isit in Honolulu?

Honolulu =Sydney - 20hr [West]= 10:20 - 20hr= -10:20+ 24:00= 14:20 yesterday

= 2:20 pm yesterday

Map

When crossing the International Date Line…

•going east – subtract (24 hours) one day•going west – add (24hrs) one day

If we look at two island nations that are about 900 kms apart.