What time is it, really?

Since 1884 Greenwich Observatory in the UK has been designated as the Prime Meridian and in consequence the point from where time is measured, calculated from midnight1.

The time in Western Australia is 8 hours ahead2 of Greenwich and is referred to GMT+8 or more precisely UTC +8.

The meridian where the time is 8 hours ahead of Greenwich is the 120° line of longitude3. This 120° line of longitude crosses Western Australia at:

Great Northern Highway 19 km east of Pardoo Roadhouse.
Ripon Hills Road 28 km east of Marble Bar.
Goldfield Highway 22 km west of Wiluna.
Mt Magnet-Leinster Road 71 km east of Sandstone.
Great Eastern Highway 33 km east of Yellowdine.
South Coast Highway 4 km west of Ravensthorpe.

It is only along this.120° line of longitude where the time is UTC+8.  Western Australia at is broadest is 1580 km wide – from Steep Point to the WA/SA border. When it is noon at 120°East, it is 11:32:38 a.m. at Steep Point and 12:36 p.m. at the border – a span of 63 minutes.

When it is noon at 120°East (GMT+8 or Australian Western Standard Time) the mean solar time in Perth (Longitude 115°51’38”, 390.5 km west of Longitude 120) is 11:43:24 a.m. At 32°South (Perth’s latitude) each degree of longitude is about 94.2 km apart. As each degree of longitude is four minutes of time3 it can be seen that the mean solar time of Kalgoorlie (529 km from Perth direct line) is about 22 minutes ahead of Perth.

 

  1. On 1 January 1972, GMT was superseded as the international civil time standard by Coordinated Universal Time (UTC) and starts at midnight.
  2. For the 350 kilometres of Eyre Highway between Caiguna and Border Village Australian Central Western Standard Time is used. This is UTC 8.75 – 45 minutes ahead of Perth.It is reputed that this came about in the time of telegraphic communications. Prior to Federation colonies were responsible for their own communications and at Eucla (virtually on the WA/SA border) telegrams from, say, WA were handed to SA operators sitting on the opposite side of the table for re-transmission. A telegram from WA that was time stamped 10:00 a.m. would be re-transmitted with the SA time of 11:30 a.m. This caused a lot of confusion that was resolved by the WA and SA Government agreeing to follow a common time at Eucla Telegraph Station midway between the two states’ official time zones. This gave rise to Australian Central Western Standard Time. This use of this quirky time zone was not repealed with the demise of the telegraph.
  3. The earth’s equator describes a circle (roughly) which is, of course, 360 degrees. However, the system of longitude uses only 180 degrees – but in two directions east and west of the Prime Meridian at Greenwich – to complete the 360 degrees of the earth’s circumference. There are 1440 minutes in a solar day (24 hours x 60 minutes = 1440 minutes).
    The 180 degrees of East longitude and the 180 degrees of West longitude = 360 degrees.
    Therefore, each degree of longitude equals four minutes of time (1440÷360).
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