Keeping an eye on Comet Holmes means keeping an eye on Algol too. The comet is in the constellation Perseus. Perseus is the wing-footed hero who saved beautiful Andromeda from the sea monster Cetus. He had first slain the evil snaky-haired Medusa, who was so ugly that anyone who looked directly at her turned to stone. Perseus chopped off her head while looking at her reflection in his shield. He then carried the head around in a bag, using it for his own advantage to turn his enemies into stone -- including Cetus. (And the lovers lived happily ever after.)
But look at the eye of Medusa on this old star map. This is the Ghoul Star, Algol (al-gol, the ghoul), supposed to be the most demonic and malevolent star in the sky, a perfect star for Halloween. Ghoulish because it changes brightness dramatically every three days, by nearly a magnitude and a half.