Earthsky.org - 10-29-13
Yes, Halloween is an astronomical holiday.
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.
Pleiades star cluster, also known as the Seven Sisters
It is 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.
