Watching the Demon Star

We are clever little apes and we've been looking at that night sky for a very long time.

Imagine a time long before electric lights and a priestly class with the time to sit out and star gaze every night.  Eventually some guy (he probably was a man) noticed a bright star in the constellation we call Perseus was a little less bright one night.  A few days later, he notices it again.  A few days after that, again.  He makes a prediction.  He tells a few priestly buddies.  Pretty soon it is common knowledge among the priests that Algol, the Demon Star, changes on a regular pattern.

From PLOS ONE:

The Ancient Egyptians wrote Calendars of Lucky and Unlucky Days that assigned astronomically influenced prognoses for each day of the year. The best preserved of these calendars is the Cairo Calendar (hereafter CC) dated to 1244–1163 B.C. We have presented evidence that the 2.85 days period in the lucky prognoses of CC is equal to that of the eclipsing binary Algol during this historical era. We wanted to find out the vocabulary that represents Algol in the mythological texts of CC. Here we show that Algol was represented as Horus and thus signified both divinity and kingship. The texts describing the actions of Horus are consistent with the course of events witnessed by any naked eye observer of Algol. These descriptions support our claim that CC is the oldest preserved historical document of the discovery of a variable star. 

Yep.  About 2600 years before the astronomical documentation of the observation, some astrologers in Egypt noticed the pattern.

We're more clever than we give ourselves credit for.  We'd do well to keep an eye on ourselves, just to make sure were not too clever for our own good.