2 thoughts on “Why Have an International Date Line?”

  1. I want to figure out that what’s the difference about international date line and prime meridian(except the location). Why does it need to named two different name,couldn’t they be the same?
    Hope you can answer me:)

  2. The IDL and Prime Meridian (GMT) exist for difference purposes. GMT (also known as UTC) exists because we need a place where longitude starts at 0 (since it’s arbitrary, unlike the equator with latitude). We also need a standard place where timezones start at zero. For various historical reasons, the powers that be chose the GMT to be that line.

    IDL, on the other hand, exists because we need an arbitrary place where one day changes into the next day (as my blog entry describes). It’s a fundamentally different purpose.

    The next obvious question, though, is: could the Prime Meridian/GMT and the IDL be the same line or do they need to be on the opposite ends of the Earth? Off the top of my head, it does seem like the IDL could be UTC-0 and Longitude 0 degrees. All of the timezone offsets would be from some point in the Pacific ocean, but otherwise it seems like it would work.

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