Did you know that 13 might be the unlucky number due to the astronomical period of the "Demon Star", also known as Algol (Beta Persei).
It was discovered already by the ancient egyptians that the star goes completely dark every thirteen days. The star was used to measure time itself, and calendars were made to predict which days were favoured by the gods. Bright Algol meant lucky days.
The principal star going dark was therefore a most unlucky omen. Even today, this happens every thirteen days, but not necessarily on every friday the 13th.
#history #astronomy #grownostr