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Happy Spooky Medieval Astronomy Day!

October 30, 2013

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.

Illustration of cross-quarter days in relation to equinoxes and solstices (Credit: NASA).

Illustration of cross-quarter days in relation to equinoxes and solstices (Credit: NASA).

Aside from Halloween, the other cross-quarter days are now known as Groundhog Day (February 2), May Day (May 1), and Lammas (August 1), and unless you get spooked by the slumbering Groundhog in early February, Halloween is probably the scariest of the cross-quarter days. The original Samhain traditionally marked the beginning of winter, and, in Western Christian cultures, included a feast for remembering the dead. All Hallow’s Eve was when saints (or, hallows), martyrs and faithful departed believers were thought to wander among the living. These departed souls were also believed to join the living during this one night to celebrate with their family, tribe or clan, then return to the land of the dead the following day (often referred to as All Saint’s, or All Hallow’s, Day).

Modern bonfire in Beltane, Scotland, commemorating the ancient rituals of Samhain (Credit: Wikipedia Commons).

Modern bonfire in Scotland for the Gaelic festival of Beltane, observing the ancient rituals of Samhain (Credit: Roger Griffith, Wikimedia Commons).

Samhain marked the end of the harvest season and the beginning of winter. Traditionally the time to take stock of food and herb supplies, and was marked by various rituals, including bonfires and divination games, it also was the boundary between light and dark, the dead and the living. The lighting of a jack-o-lantern in fact originates back to the tradition of frightening evil spirits on All Hallow’s Eve.

Snap-Apple Night (1833), painted by Daniel Maclise, shows people in Ireland playing divination games October 31. The painting  was inspired by a Halloween party the artist  attended in Blarney, Ireland, in 1832 (Credit: Wikipedia Commons).

Snap-Apple Night (1833), painted by Daniel Maclise, shows people playing divination games on October 31 in Ireland. (Source Wikimedia Commons)

History aside, there are other, perhaps more tangible, and certainly aesthetically beautiful connections between astronomy and Halloween. One particularly glorious example is the Witch Head Nebula, named for its resemblance to a fairy tale witch’s head (rightward facing, chin at bottom):

The Witch Head Nebula derives its name due to its resemblance to a witch's head (right-facing in this image, chin at bottom). Also known as IC 2118, this reflection nebula in the constellation Orion reflects mostly blue light due to both its central star and from dust grains in the nebula, similar to how our sky looks blue from reflected sunlight (Credit: NASA/STScI).

The Witch Head Nebula derives its name due to its resemblance to a witch’s head (right-facing, large nose at center, chin at bottom). Also known as IC 2118, this reflection nebula in the constellation Orion reflects mostly blue light due to both its central star and from dust grains in the nebula, similar to how our sky looks blue from reflected sunlight (Credit: NASA/STScI).

Another aptly spooky supernova remnant is the Veil Nebula. Near the constellation Cygnus, the portion of the Eastern Veil shown gloriously below, spans only about 1/2 degree in the sky, about the size of the Moon.

While perhaps “veil-like”, I see more of a bat with wings extended:

In this composite of image of the Veil Nebula, data are recorded through narrow band filters. Emission from hydrogen atoms in the remnant is shown in red with strong emission from oxygen atoms in blue-green hues. In the western part of the Veil lies another seasonal apparition, the Witch's Broom (Credit: NASA APOD/Alfonso Carreño).

In this composite of image of the Veil Nebula, data are recorded through narrow band filters. Emission from hydrogen atoms in the remnant is shown in red with strong emission from oxygen atoms in blue-green hues (Credit: NASA APOD/Alfonso Carreño).

In the western part of the Veil lies another seasonal apparition, the Witch’s Broom, another portion of the same remnant, this time resembling, you guessed it, a witch’s broom, with the sweeping end of the broom facing bottom right of the image:

Imaged with narrow band filters, the glowing filaments are like long ripples in a sheet seen almost edge on, remarkably well separated into atomic hydrogen (red) and oxygen (blue-green) gas (Credit: NASA, APOD/Martin Pugh).

Imaged with narrow band filters, the glowing filaments are like long ripples in a sheet seen almost edge-on, remarkably well separated into atomic hydrogen (red) and oxygen (blue-green) gas (Credit: NASA APOD/Martin Pugh).

Finally, the “Ghost Head” Nebula, or NGC 2080, is a star-forming region staring menacingly from the Large Magellanic Cloud, a satellite galaxy of the Milky Way. The glowing eyes of the “ghost” are called A1, the western patch, called A1, which has a bubble in the center that was created by the young, massive star it contains. The eastern patch, called A2, is composed of a cluster of several young stars.

The Ghost Head Nebula spans about 50 light years in the Large Megellanic Cloud (Credit: NASA/APOD/ESA/Mohammad Heydari-Malayeri et al. 2007).

The Ghost Head Nebula spans about 50 light years in the Large Megellanic Cloud (Credit: NASA/APOD/ESA/Mohammad Heydari-Malayeri et al. 2007).

So how astronomically spooky will tomorrow night be? Well, the star Algol, fittingly known as the “Demon Star”, will be up for a few hours centered on 10:35 PM Eastern Time, in the constellation Perseus.

Algol (center right in image) in the constellation Perseus (Credit: Wikipedia Commons).

Algol (right, center) in the constellation Perseus (Credit: Torsten Bronger)

Algol is in fact a triple star system, with designated component stars, A and B. The animation below shows a ghost-like Algol B orbiting the brighter Algol A.

Algol is actually a binary star, with designated component stars, A and B, with Algol B orbiting Algol A. This animation was assembled from 55 images of the CHARA interferometer in the near-infrared hydrogen band. Because some phases are poorly covered, B jumps at some points along its path (Credit: Wikipedia Commons).

This animation was assembled from 55 images of the CHARA interferometer in the near-infrared hydrogen band. Because some phases are poorly covered, B jumps at some points along its path (Credit: Dr. Fabien Baron, Dept. of Astronomy, University of Michigan, Ann Arbor, MI 48109-1090, labels indicating phase added by Wikipedia user:Stigmatella aurantiaca).

But worry not, the superstitious among you. Werewolves will be kept at bay while you trick-or-treat or otherwise celebrate this year’s All Hallow’s Eve — October 31, 2013 will be virtually Moonless.

So, if you celebrate Halloween in all its ghoulish glory, if it’s an afterthought, or even if you give it no thought at all, have a safe, happy, astronomically fun day tomorrow!

*    *    *    *    *    *    *    *    *    *    *    *

Halloween.
Sly does it. Tiptoe catspaws. Slide and creep.
But why? What for? How? Who? When! Where did it all begin?
‘You don’t know, do you?’ asks Carapace Clavicle Moundshroud climbing out
under the pile of leaves under the Halloween Tree. ‘You don’t really know!”
—Ray Bradbury, The Halloween Tree

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