[Ansteorra] The Equinox

[Galen of Ockham, OP]

   Your calendar most likely has the 'beginning of spring' or 'equinox'
   annotated on the 19th or 20th of March, but your medieval calendar
   should have it permanently inked in on the 21st.


   The equinoxes are the two points of the year when the Sun is halfway
   between its furthest north point (the summer solstice in June), and its
   furthest south travel (winter solstice in December). It's commonly said
   that these days have equal hours of light and darkness, but that's not
   strictly true. The time between sunrise and sunset are very close to 12
   hours on the equinoxes at all points on the globe, but since we still
   get some light refracted through the atmosphere before sunrise and
   after sunset the hours of light are somewhat longer than 12 hours.


   Astronomically, the equinox is the moment when the Sun crosses the
   plane of the Earth's equator. The Vernal (spring) Equinox occurred this
   year at 1:13 AM on Tuesday March 20 on the east coast of the US, or
   10:13 pm Monday March 19 Pacific time. The Council of Nicaea (325 AD)
   fixed the date of the equinox as March 21 for the calculation of the
   date of Easter (based on ancient Babylonian measurements). The exact
   time and date of the equinox drifts slowly due to an effect called
   precession. Easter was eventually defined as the first Sunday following
   the first full moon after the Equinox. (However, like the Equinox, the
   full moon is also a calculated phenomenon that doesn't necessarily
   match the actual date.) Using this formula, Easter can occur anywhere
   between March 22 and April 25. This year it occurs on April 8.


   Being able to accurately determine the date of Easter was a very strong
   driving force behind the study of Astronomy in medieval times. Many
   controversies of the early Church were over the date of Easter. Perhaps
   I'll discuss the Quartodeciman controversy as we get closer to Easter.

   --

   Magister Galenus Ockhamnesis
   Friar Galen of Ockham, OP
   A Study in Natural Philosophy: [1]http://medievalscience.org
   Chirurgeon's Point: [2]http://chirurgeon.org

   xb

References

   1. http://medievalscience.org/
   2. http://chirurgeon.org/