Ancient Egyptian astronomers may have discovered variable stars, and calculated the period of a well-known one called Algol, thousands of years before Europeans -- and it was closely linked to the god Horus.
Ancient Egyptian astronomers may have discovered variable stars, and calculated the period of a well-known one called Algol, thousands of years before Europeans. But they buried those observations in a calendar designed to predict lucky and unlucky days, wrapped in religious narratives, so it's taken some work for modern scholars to tease out the hidden discovery.
Not all of the stars in the night sky shine steadily. Some, called variable stars, appear to fade and brighten at regular intervals. These stars are actually part of binary systems, and when the dimmer member of the pair passes between us and its brighter sibling, it causes an eclipse, so the bright star seems to fade from the night sky for a few minutes or hours. European astronomers first described a variable star called Mira in 1596, and another called Algol in 1669. John Goodricke calculated the orbital period of Algol's two stars over a century later, in 1783 -- but it turns out the ancient Egyptians had worked that out over a millennium and a half earlier.
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