October can be eerie, all right. Down on Earth the chill winds blow and the fall colors vanish, replaced by stark, barren branches. In the sky too, it’s a perfectly spooky month--the ideal backdrop for the autumn night when the most people roam beneath the stars: Halloween.
The month begins creepily enough. Nightfall finds Scorpius the Scorpion slithering downward into the southwestern horizon. Draco the Dragon hangs high in the northwest, and low in the west stands Boötes (pronounced boo!-o-teez). The sky’s eeriest props are in place.
But the celestial object most intimately connected with devils and witches waits until mid-month to rise at nightfall, so that by Halloween it’s well up when darkness comes. It’s the Pleiades.
What? That close-knit cluster of young suns better known as the Seven Sisters? What have they to do with sinister things? In the Western world, everything. Halloween revolves around them.
Even without Halloween, other cultures attached significance to the Pleiades. The Brahmans of ancient India visualized those stars as the sparks of Agni, the god of fire. In Greek legend they were the daughters of Atlas. The Pleiades are even mentioned in the Book of Job:
Canst thou bind the sweet influences of Pleiades, or loose the bands of Orion?
A sweet influence is hardly scary. But some cultures associated the Pleiades with more ominous occasions. The Aztecs, for example, linked the date when the constellation reached its highest point, or culminated, at midnight with the end of the world. The Aztecs believed that every 52 years, when their 365-day sun calendar and 260-day ritual calendar came into coincidence, the possibility existed that the heavens would cease to move and demons would fall from the sky. The sign that this catastrophe wouldn’t befall the cosmos? When the Pleiades reached their zenith at midnight (almost straight overhead in Mexico City) and then continued harmlessly across the sky.
The Aztec ceremony associated with this event involved a human sacrifice. That’s certainly creepy but has nothing to do with Halloween. For that, we must look to the Celts.
Many historians believe Halloween is the modern-day remnant of a Celtic celebration called Samhain, which marked the end of the Celtic year and the transition from summer to winter. The Celts believed that during Samhain, the border between this world and the supernatural world cracked open, granting free passage to sinister fairies from the land of the dead. Samhain fell at the midpoint between the autumnal equinox and the winter solstice, and the Celts originally knew when that was because it took place at the same time that--you guessed it--the Pleiades culminated at midnight.
The tradition, developed in the Middle Ages, of the Witches’ Sabbath on October 31 is probably rooted in the old Celtic observance. That date was upheld into modern times as All Hallows’ Eve, which became, of course, Halloween.
Now is your chance to get closer to the power behind the goblins and mischief of October’s final night. The Pleiades are striking to the unaided eye, but they become stunning through binoculars. Instantly the six to eleven naked-eye stars grow to hundreds of sapphire jewels.
Astronomy clubs periodically hold observing nights for the public. Perhaps some will set up instruments on Halloween, so families-- already outdoors on their diabolic rounds--can bravely meet October’s ghostly apparitions face-to-face.