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Halloween is a cross-quarter day |
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October 31, 2017 |
By Bruce McClure
EarthSky.org
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| NASA
illustration |
| Equinoxes,
solstices and cross-quarter days are all
hallmarks of Earth’s orbit around the
sun. Halloween is the 4th cross-quarter
day of the year. |
Halloween – short for All Hallows’ Eve – is an
astronomical holiday. Sure, it’s the modern-day
descendant from Samhain, a sacred festival of
the ancient Celts and Druids in the British
Isles. But it’s also a cross-quarter day, which
is probably why Samhain occurred when it did.
Early people were keen observers of the sky.
A cross-quarter day is a day more or less midway
between an equinox (when the sun sets due west)
and a solstice (when the sun sets at its most
northern or southern point on the horizon).
Halloween – October 31 – is approximately midway
point between the autumn equinox and winter
solstice, for us in the Northern Hemisphere.
In other words, in traditional astronomy, there
are eight major seasonal subdivisions of every
year. They include the March and September
equinoxes, the June and December solstices, and
the intervening four cross-quarter days.
In modern times, the four cross-quarter days are
often called Groundhog Day (February 2), May Day
(May 1), Lammas (August 1) and Halloween
(October 31).
For us in the Northern Hemisphere, Halloween is
the darkest of the cross-quarter days, coming at
a time of year when the days are growing
shorter. Early people once said that the spirits
of the dead wander from sunset until midnight
around this cross-quarter day. After midnight –
on November 1, which we now call All Saints’ Day
– the ghosts are said to go back to rest.
The October 31 date for Halloween has been fixed
by tradition. The true cross-quarter day falls
on November 7, representing a discrepancy of
about a week. According to the ancient Celts, a
cross-quarter day marks the beginning – not the
middle – of a season.
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| Dave Dehetre
photo |
| The Pleiades
star cluster, also known as the Seven
Sisters. This tiny, misty dipper is easy
to pick out in the night sky. |
It’s thought that the early forbearer of
Halloween – Samhain – happened on the night that
the Pleiades star cluster culminated at
midnight.
In other words, the Pleiades climbed to its
highest point in the sky at midnight on or near
the same date as this cross-quarter day. In our
day, Halloween is fixed on October 31, though
the midnight culmination of the Pleiades cluster
now occurs on November 21.
Presuming the supposed connection between
Samhain and the midnight culmination of the
Pleiades, the two events took place on or near
the same date in the 11th century (1001-1100)
and 12th century (1101-1200). This was several
centuries before the introduction of the
Gregorian calendar.
At that time, when the Julian calendar was in
use, the cross-quarter day and the midnight
culmination of the Pleiades fell – amazingly
enough – on or near October 31. But, then, the
Julian calendar was about one week out of step
with the seasons. Had the Gregorian calendar
been in use back then, the date of the
cross-quarter day celebration would have been
November 7.
But Halloween is now fixed on October 31.
Meanwhile, the true cross-quarter day now falls
on or near November 7 and the midnight
culmination of the Pleiades cluster on or near
November 21. |
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