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Equinox date

  • 29-02-2016 10:52pm
    #1
    ezra_pound
    Registered Users, Registered Users 2 Posts: 2,497 ✭✭✭


    So as far as I knew the equinox was always the 20th or 21st march. It looks like march 17 has equal day and night though, not the other two dates, sunrise to sunset being 6:33 to 18:33. Surely that would make it the equinox.

    Where am I going wrong with this?


Comments

  • #2
    Rougies
    Registered Users, Registered Users 2 Posts: 2,735 ✭✭✭Rougies


    ezra_pound wrote: »
    So as far as I knew the equinox was always the 20th or 21st march. It looks like march 17 has equal day and night though, not the other two dates, sunrise to sunset being 6:33 to 18:33. Surely that would make it the equinox.

    Where am I going wrong with this?

    The main reason is because sunrise time is measured when the top of the sun rises above the horizon and sunset is measured when the top of the sun lowers below the horizon, which adds a few minutes to the time the center point of the sun rises and sets. Simply put, the equinox is the day when the center point of the sun crosses above and below the horizon at exactly 12 hour intervals.


  • #3
    ezra_pound
    Registered Users, Registered Users 2 Posts: 2,497 ✭✭✭ezra_pound


    Rougies wrote: »
    The main reason is because sunrise time is measured when the top of the sun rises above the horizon and sunset is measured when the top of the sun lowers below the horizon, which adds a few minutes to the time the center point of the sun rises and sets. Simply put, the equinox is the day when the center point of the sun crosses above and below the horizon at exactly 12 hour intervals.

    Thanks


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