Spooky astronomy

Halloween is date of astronomical interest. It has to do with seasons: Halloween is a cross-quarter date, approximately midway between an equinox and a solstice. There are four cross-quarter dates throughout the year, and each is a minor holiday: Groundhog Day (Feb. 2nd), May Day (May 1st), Lammas Day (Aug. 1st), and Halloween (Oct. 31st).

"Long ago, the Celts of the British Isles used cross-quarter days to mark the beginnings of seasons. Winter began with Halloween, or as they called it, Samhain," says John Mosley of the Griffith Observatory. "Halloween marked the transition between summer and winter, light and dark -- and life and death. On that one night, according to folklore, those who had died during the previous year returned for a final visit to their former homes. People set out food and lit fires to aid them on their journey -- but remained on guard for mischief the spirits might do."

And so something astronomical became something spooky. It's not the first time. Happy Halloween!