Longitude and time difference At this time of

Longitude and time difference 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 (24 h): 360º = 24 h ÷ 24 15º = 1 h 1º = 4 min ÷ 15 also 1 hour = 60 min

Longitude and time difference 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.

Example 1 a) Sydney is 10 hours ahead of GMT, or GMT +10 h. i) If it is 8 am in London, what time is it in Sydney? ii) If it is 5 pm Saturday in London, should you ring Sydney? i) 0800 + 1000 = 1800 or 6 pm As Sydney is east of ii) 1700 + 1000 = 2700 London add the time = 3 am Sunday morning don’t ring mum at this time. b) New York is GMT 5 h and Moscow is GMT +3 h. i) If it is 4 pm in Moscow, what time is it in New York? ii) If it is 2 am Friday in Moscow, what time is it in New York? 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. 5 + 3 = 8 hour difference i) 1600 0800 = 0800 or 8 am ii) 0200 0800 = 0600 = 1800 Thursday or 6 pm Thursday

Example 2 Rio de Janeiro is GMT 3 h and Los Angeles is 8 h. i) If it is 7 am in Rio, what time is it in LA? ii) If it is 9 pm 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. 8 3 = 5 hour difference i) Going from Rio to LA you are heading west subtract the time difference. 0700 0500 = 0200 or 2 am ii) Going from LA to Rio you are heading east add the time difference. 2100 + 0500 = 2600 = 0200 Wednesday or 2 am Wednesday iii) As 1 h = 15º and GMT xh means you are west of Greenwich LA: 8 × 15 = 120 Rio: 3 × 15 = 45 Rio is approximately 45ºW LA is approximately 120ºW

Example 3 If it is 10 am 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 = 4 min 83 × 4 = 332 min = 5 h 32 min From Hong Kong you head west to Durban Subtract the time difference 1000 0532 = 0428 or 4: 28 am

Example 4 New Orleans is (30ºN, 90ºW) and Karachi is (24ºN, 67ºE). i) If it is 7: 27 am in New Orleans what time is it in Karachi? ii) If it is 2: 14 am in Karachi what time is it in New Orleans? As the 2 cities are on different sides of the Greenwich meridian 90 + 67 = 157º add the angles. As 1º = 4 min 157 × 4 = 628 min = 10 h 28 min i) From New Orleans you head east to Karachi add the time difference 0727 + 1028 = 1755 or 5: 55 pm the same day ii) From Karachi you head west to New Orleans subtract the time dif. 0214 1028 = 0814 = 1546 the previous day or 3: 46 pm the previous day

Today’s work Exercise 7 -04 Page 265 → 266 Q 1 → 5, 7 → 10, 12 → 15 & 17