i'm attempting to create a script for easily calculating the southern hemisphere equivalent of shrove tuesday.i'm attempting to create a script for easily calculating the southern hemisphere equivalent of shrove tuesday.
the date of ash wednesday is determined by counting backwards from the date of easter. shrove tuesday is the day before ash wedesday. there are many programs and web scripts that will easily let you determine the date of easter, but the problem with these is that they are all based upon northern hemisphere traditions. since historical evidence strongly suggests that easter came to be named and scheduled as it is due to already existing pagan customs celebrating the coming spring during Eostur-monath (april), it makes sense to adjust these dates to account for the differing seasons in the southern hemisphere.
i'm keeping my calculations simple and using the basic rule given by bede for the date of easter: The Sunday following the full Moon which falls on or after the equinox will give the lawful Easter. the churchy folks in the northern hemisphere actually make it a lot more complex than that because they decided that the vernal (spring) equinox should be considered to always be on march 21st (when it can actually fall on the 20th, 21st or 22nd of march) and their "paschal full moon" does not even necessarily fall on the day of a true full moon. you can read all about that on wikipedia, if you're so inclined.
so my 'formula' for working this out goes along these lines:
start at: spring equinox
(southern hemisphere seasons)
determine: full moon
that occurs either on or after the date of the equinox
determine: sunday
after the full moon
this is our southern hemisphere "easter"
count back: 46 days
this is forty days if you exclude the sundays.. which you do
this is the date of ash wednesday, the first day of lent
count back: 1 day
this is shrove tuesday. let's eat pancakes!
i'm still working on this bit. i'm using the Astro_MoonPhase class to calculate the full moon after the equinox and from there it's easy enough to use native php functions to count the days backwards.
unfortunately i haven't yet found a way of automatically calculating the date of the equinox (that i can understand), which would mean the calculations could be astronomically correct depending on your location/timezone. so for the moment i'm manually entering the equinox date and it's based on brisbane, qld, australia; and that's why there are only a few year's worth of dates.
2011
Vernal equinox is on September 23rd at 19:04
Full moon is on October 12th (Wednesday)
Easter is on October 16th (Sunday)
Ash Wednesday is on August 31st
Shrove Tuesday is on August 30th 2011
2012
Vernal equinox is on September 23rd at 00:49
Full moon is on September 30th (Sunday)
Easter is on October 7th (Sunday)
Ash Wednesday is on August 22nd
Shrove Tuesday is on August 21st 2012
2013
Vernal equinox is on September 23rd at 06:44
Full moon is on October 19th (Saturday)
Easter is on October 20th (Sunday)
Ash Wednesday is on September 4th
Shrove Tuesday is on September 3rd 2013
2014
Vernal equinox is on September 23rd at 12:29
Full moon is on October 8th (Wednesday)
Easter is on October 12th (Sunday)
Ash Wednesday is on August 27th
Shrove Tuesday is on August 26th 2014
© 2011 jade e. leth
yes, i am aware of the irony of calculating southern hemisphere equivalents for "stolen" pagan festivals turned into christian celebrations. that's kind of why it's fun.
also, it's another excuse to eat pancakes.