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Open Astronomy

formerly Baltic Astronomy

Editor-in-Chief: Barbuy, Beatriz

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Volume 27, Issue 1


Algol as Horus in the Cairo Calendar: The Possible Means and the Motives of the Observations

Sebastian Porceddu / Lauri Jetsu / Tapio Markkanen / Joonas Lyytinen / Perttu Kajatkari / Jyri Lehtinen / Jaana Toivari-Viitala
Published Online: 2018-09-19 | DOI: https://doi.org/10.1515/astro-2018-0033


An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck with the period of 2.850 days. Previous astronomical, astrophysical and statistical analyses of CC support the idea that this was the period of the eclipsing binary Algol three millennia ago. However, next to nothing is known about who recorded Algol’s period into CC and especially how. Here, we show that the ancient Egyptian scribes had the possible means and the motives for such astronomical observations. Their principles of describing celestial phenomena as activity of gods reveal why Algol received the title of Horus.

Keywords: Algol; Horus; ancient Egyptian Astronomy; variable stars; the Cairo Calendar; hemerologies


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About the article

Received: 2018-02-15

Accepted: 2018-05-04

Published Online: 2018-09-19

Published in Print: 2018-09-01

Citation Information: Open Astronomy, Volume 27, Issue 1, Pages 232–263, ISSN (Online) 2543-6376, DOI: https://doi.org/10.1515/astro-2018-0033.

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