Happy Equinox!

by Deb on September 23, 2010

Post image for Happy Equinox!

Today is the September Equinox, so here is some equinoctial trivia.

  1. The exact time of this equinox is September 23rd, 1:09pm Australian Eastern Standard Time (here is a converter if you want to find out for where you are).
  2. The equinox is when the centre of the sun appears directly overhead at a point on the equator.
  3. Because the sun is a large sphere not a point, it is actually above the equator for about 33 hours.
  4. There are roughly 12 hours of day and night on the equinox, but not exactly.  This is because it is measured from the middle of the sun, and when the middle of the sun is on the horizon half of it is above.  So the day of the equinox is slightly longer than the night.
  5. The day with 12 hours between sunrise and sunset is called the equilux and will be a few days before the spring equinox and a few days after the autumn equinox.  It changes depending where you are on earth.
  6. The sun, of course, does not actually move.  What is really happening at the equinox is the tilt of the earth’s axis is sideways to the sun, rather than towards it as it is during the Solstice.  You can see this in the picture above.
  7. On the equinoxes the sun will rise due east and set due west.
  8. Some countries begin their seasons based on the equinoxes and solstices, so for those countries today is the beginning of autumn or spring (we started spring 3 weeks ago in Australia).
  9. All planets with an axial tilt will have a noticeable equinox.  Saturn’s is spectacular because there is no sunlight on the rings.
  10. The equinox can disrupt communications satellites – geostationary satellites orbit in the same plane as the equator and will have the sun directly behind them for certain times around the equinox.  The sun is so much more powerful than the satellite signal it can overwhelm the earth station receiver.
  11. Because of its association with Autumn in the Northern Hemisphere there are many harvest festivals associated with the September equinox around the world.
  12. The reason the date of the equinoxes jumps around is because the solar year is not exactly 365 days.  They shift by a full day in roughly 70 years, which is reset by the leap years and leap centuries.
  13. It has been 94 days since the June Solstice, but there are only 89 days between the December Solstice and March equinox.  The seasons are different lengths because the earth’s speed varies during its orbit.
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