Friday, March 21 brings us the first full moon of the new spring season, the vernal equinox having already occurred on March 20 at 1:49 a.m. EDT (or on March 19 if you live in the Mountain, Pacific or Alaskan-Hawaii time zones).
The official moment that the moon will turn full on March 21
is 2:40 p.m. EDT (though in reality it's never actually
full).
The first full moon of spring is sometimes referred to as
the Paschal full moon; the moon that is used to set the date of Easter in a
given year. This year, if you have not already noticed, Easter is going to
arrive unusually early. If you're 50 years old or younger, the earliest Easter
in your lifetime came on March 26 (in 1967, 1978 and 1989). In 1951, Easter
fell on March 25; in 1940, March 24.
But in 2008, Easter will arrive on March 23. So early in
fact, that Palm Sunday, which is observed on the Sunday before Easter, was
celebrated this year on the day before Saint Patrick's Day; a calendrical
oddity.
The last time that Easter fell this early in the calendar
was 1913. And before that, in 1856.
Which leads one to ask the question, exactly just how is the
date of Easter determined?
Equinox and full moon are the keys
Traditionally, Easter is observed on the Sunday after the
Paschal full moon. If the Paschal moon occurs on a Sunday, Easter is the
following Sunday.
Following these rules, we find that Easter can fall as early
as March 22 and as late as April 25. Pope Gregory XIII decreed this in 1582 as part
of the Gregorian calendar.
As we already have noted, in 2008, the Paschal full moon
occurs on Friday, March 21. So according to the current ecclesiastical rules
Easter is to be celebrated two days later, on Sunday, March 23.
Interestingly however, these rules also state that the
vernal equinox is fixed on March 21, even though at European longitudes from
the years 2008 through 2101 it actually will occur no later than March 20.
Hence, there can sometimes be discrepancies between the
ecclesiastical and astronomical versions for dating Easter. In the year 2038, for
instance, the equinox falls on March 20 with a full moon the next day, so
astronomically speaking, Easter should fall on March 28 of that year. In
reality, however, as mandated by the rules of the Church, Easter in 2038 will
be observed as late as it can possibly come, on April 25!
Adding additional confusion is that there is also an
"ecclesiastical" full moon,
determined from ecclesiastical tables and whose date does not necessarily
coincide with the "astronomical" full moon, which is based solely on
astronomical calculations. In 1981, for example, the full moon occurred on
Sunday, April 19, so Easter should have occurred on the following Sunday, April
26. But based on the ecclesiastical full moon it occurred on the same day of
the full moon, April 19!
So, in practice, the date of Easter is determined not from
astronomical computations, but rather from other formulae such as Epacts and
Golden Numbers. In 2008, we are in Epact 22 and the Golden Number is 14.
Since the beginning of the 20th century, a proposal to
change Easter to a fixed holiday rather than a movable one has been widely
circulated, and in 1963 the Second Vatican Council agreed, provided a consensus
could be reached among Christian churches. The second Sunday in April has been
suggested as the most likely date.
Changeable weather, too!
Interestingly, the fact that Easter occurs at a time of the
year when weather patterns are transitioning from winter to spring, means a
wide variation in the type of weather that can be expected, depending upon just
when the holiday occurs in a given year. Ask somebody what type of weather
immediately comes to mind when Christmas is mentioned, and likely the answer
will be cold and snowy. For the Fourth of July: probably sunny and hot.
Yet, Easter can feature both of these extremes!
In 1970, Easter fell on March 29. In that year, a snowstorm
hit the Northeastern U.S. In New York City, the famous Easter Parade had to be
cancelled, as four inches of snow fell, with as much as a foot of the white
stuff in the northern suburbs.
And yet, just six years later, in 1976, Easter fell on April
18, which ended up going down in New York weather annals as the hottest Easter
on record. Not only was the 96-degree reading that day the hottest temperature
recorded in Central Park that year, it also was the very first (and only time)
that New York held the distinction of being the hottest location in the United
States!
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other
publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.
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