Saturday, 21 December 2013

Solstice: It's not always the 21st, and other interesting facts

Here's some facts about solstice before I get to bed, ahead of getting up for sunrise, the same as the last 9!
  • Solstice is a moment in time...
    when the Earth is either pointed the most towards or the most away from the sun as possible.
    For December 2013, the moment is 17:11 UTC (GMT) on Sat 21st

  • So the longest day is 20th, or 21st, or 22nd
    ...depending how far east or west you are.
    If you're on the USA's west coast (UTC -8hrs), this is sometimes on 20th of June/December.
    If you're in New Zealand (UTC +12hrs, +13 in summer!) this is often on 22nd. Like today!

  • Don't forget leap years
    A year is 365.25 days long, roughly. So 3 years are 365 days, and every 4th year adds a day.
    So solstice goes forward by 6hrs for 3 years in a row, then goes back 18hrs every leap year!

    Confused? Check out these times & dates for the March equinox...

    2012: 05:14 UTC 20th March (leap year)
    2013: 11:02 UTC 20th
    2014: 16:57 UTC 20th
    2015: 22:45 UTC 20th
    2016: 04:30 UTC 20th (leap year)

    For anyone west of Chicago (UTC -6hrs) , leap year March equinoxes are actually 19th!

    ...and December solstice:

    2012: 11:12 UTC 21st December (leap year)
    2013: 17:11 UTC 21st
    2014: 23:03 UTC 21st
    2015: 04:48 UTC 22nd
    2016: 10:44 UTC 21st (leap year)

    For New Zealand, all of these solstices are on 22nd December, because NZ is UTC +13 hrs (+12 time zones +1hr daylight savings).
    For Australia (UTC +8, +9, +10) the leap years are 21st December, but the rest are 22nd!

  • Equinox is the halfway point
    Autumn and spring equinoxes are moments in time, like winter and summer solstice...

  • Equilux is equal day & night
    ...but equal day and night is actually the equilux, which is either a few days later or earlier, because of weird sciency stuff
And now you know some stuff about solstice.
Time to get to bed! Happy solstice everyone, winter or summer!

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