Happy Spooky Medieval Astronomy Day!
Originally posted on Research & Collections:
BOO! The origins of Halloween can be traced back to medieval European astronomical calendars.
Surprised? Indeed, there’s not much astronomy in sticky-fingered pint-sized ghosts knocking on your door begging for candy. But the historical roots between Halloween — or, Hallowe’en, a contraction of All Hallow’s Evening (or, All Hallow’s Eve) — and astronomy trace back to medieval astronomical divisions of a year, and to festivals with Gaelic, Pagan, and Christian influences. In fact, the assimilation into North American culture of Halloween as we know it today, with a wide range of both frightening and humorous costumes, as well as trick-or-treating, did not happen until the late 19th to early 20th centuries.
The astronomical roots of the Gaelic, or Celtic harvest festival, Samhain — known as the “Lord of Darkness” in Ireland, from which Halloween derives, are found in its placement in the medieval calendar year as one of four cross-quarter days, where it remains today. As the name implies, cross-quarter days fall between the four quarter days — days separated by roughly three months and near the two solstices (highest or lowest point of the Sun in the sky, in June and December) and two equinoxes (the point at which the Earth’s equatorial plane passes the center of the Sun such that the Earth is neither tilted toward nor away from the Sun, in March and September). Quarter days were originally religious festivals, and, while now limited in significance, leasehold payments and rents for land and premises in England are often still due on the old English quarter days.