At this time of the year, Australia has 3 time zones, Eastern, Central and Western Standard Times. This is because as the sun rises over Sydney it is still dark in Adelaide and Perth. Approximately 1 hour later, the sun rises in Adelaide, but it is still dark. It is approximately another hour before the sun rises in Perth.Today we will “ignore time zones”, but look at how we can work out time differences.Melbourne, Canberra, Sydney and Brisbane have approx. the same longitude so there is almost no time difference between the cities.Time difference occurs if there is a difference in longitude.As the earth completes one full revolution (360º) in one day (24h):

360º = 24h 15º = 1h 1º = 4min

Longitude and time difference

÷ 24÷ 15 also 1hour = 60 min

Around the world local times are measured in relation to the time along the Greenwich Meridian. This is called Greenwich Mean Time, GMT, or Universal Time, UT.Locations to the east of the Greenwich Meridian are ahead of GMT.This is because the sun rises in the east.Locations to the west of the Greenwich Meridian are behind GMT.Therefore if you head EAST you ADD the time difference between two locations. If you head WEST you SUBTRACT the time.

Longitude and time difference

Example 1a) Sydney is 10 hours ahead of GMT, or GMT +10h.

i) If it is 8am in London, what time is it in Sydney?ii) If it is 5pm Saturday in London, should you ring Sydney?

i) 0800 + 1000 = 1800 or 6pmii) 1700 + 1000 = 2700

= 3am Sunday morning don’t ring mum at this time.

b) New York is GMT 5h and Moscow is GMT +3h.i) If it is 4pm in Moscow, what time is it in New York?ii) If it is 2am Friday in Moscow, what time is it in New York?

As Sydney is east of London add the time

0600= 1800 Thursday or 6pm Thursday

As New York is west of Moscow subtract the time difference.As the 2 cities are on different sides of the Greenwich meridian ADD the time differences.

i) 1600 0800 = 0800 or 8amii) 0200 0800 =

5 + 3 = 8 hour difference

Example 2Rio de Janeiro is GMT 3h and Los Angeles is 8h.

i) If it is 7am in Rio, what time is it in LA?ii) If it is 9pm Tuesday in LA, what time is it in Rio?iii) What are the approximate longitudes of Rio and LA

As the 2 cities are on the SAME sides of the Greenwich meridian so SUBTRACT the time differences.

i) Going from Rio to LA you are heading west subtract the time difference.

0700 0500 = 0200 or 2am

8 3 = 5 hour difference

ii) Going from LA to Rio you are heading east add the time difference.

2100 + 0500 = 2600= 0200 Wednesdayor 2am Wednesday

iii) As 1h = 15ºRio: 3 × 15 = 45Rio is approximately 45ºW

and GMT xh means you are west of GreenwichLA: 8 × 15 = 120LA is approximately 120ºW

Example 3If it is 10am in Hong Kong (22ºN, 114ºE), what time is it in Durban(29ºS, 31ºE), ignoring time zones.As the 2 cities are on the SAME sides of the Greenwich meridian SUBTRACT the angles.

114 31 = 83º As 1º = 4min 83 × 4 = 332 min

= 5h 32min

From Hong Kong you head west to Durban Subtract the time difference

1000 0532 = 0428or 4:28am

Example 4New Orleans is (30ºN, 90ºW) and Karachi is (24ºN, 67ºE).i) If it is 7:27am in New Orleans what time is it in Karachi?ii) If it is 2:14am in Karachi what time is it in New Orleans?As the 2 cities are on different sides of the Greenwich meridian add the angles. 90 + 67 = 157º

As 1º = 4min 157 × 4 = 628 min

= 10h 28mini) From New Orleans you head east to Karachi

0727 + 1028 = 1755or 5:55pm the same day

add the time difference

ii) From Karachi you head west to New Orleans 0214 1028 = 0814

= 1546 the previous dayor 3:46pm the previous day

subtract the time dif.

Today’s workExercise 7-04

Page 265 → 266Q1 → 5, 7 → 10, 12 → 15 & 17