• Question: Where is all time measured from?

    Asked by jessohbrien to Carol, Ellie, John, Philip, Rebecca on 2 Jul 2012.
    • Photo: Rebecca Lacey

      Rebecca Lacey answered on 2 Jul 2012:

      Hi jessohbrien

      All time is measured from Greenwich in London, more specifically the Greenwich Meridian Line. All other time zones are then compared to this one.

      Greenwich Mean Time (GMT) was established in 1884. GMT is the the average time that the earth takes to rotate from noon-to-noon

    • Photo: Carol White

      Carol White answered on 2 Jul 2012:

      Geographically… from GMT – Greenwich Mean Time which is where we measure the start and end of a day – it runs through London! SO we measure Australia as being “ahead” of time and the USA as “behind”.

      Archaeologists and scientists think people started measuring time as early as 6000 years ago, when people used to moon to measure months. Julius Caesar (in about 45 BC) made the the Roman world a solar calendar but it was a Pope who added some corrections to make what we call a calendar today!

    • Photo: John Welford

      John Welford answered on 2 Jul 2012:

      As the others have said, world times are set relative to GMT. But to measure the passing of time we use seconds. Minutes, hours, etc, are defined as a set number of seconds.

      The second is one of seven fundamental physical quantities that are used in measurement (other examples are metres and kilograms) and loads of other quantities are based on the second (like velocity).

      Clocks can work in lots of different ways to measure seconds including swinging of pendulums and vibrations of quartz crystals. The official definition of a second, that all other seconds are measured against, is based on the radiation of a caesium atom at a fixed temperature. That’s not very practical to put in most clocks though.

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