Ancient Egyptian Papyrus Describes Algol’s Variability 3,000 Years Before Western Astronomers

This ancient text could be the oldest record of Algol's variable brightness observations, a triple star system known as "the Demon Star."

Fixed star Algol, Beta Persei, is a 2.1 magnitude, rare triple star and eclipsing binary, found in the Medusa’s Head, carried in the left hand of the Hero, Perseus Constellation.

The name Algol originates from the Arabic word رئيس الغول, which translated means the Head of the Ogre.

The English translation is the Demon Star, with other names being Satan’s Head, the Spectre’s Head.

For the ancient Chinese it belonged to s group of stars referred to as the Mausoleum.

In the night sky, Algol appears to blink.

Every 69 hours, its magnitude dips for about 10 hours before returning to full brightness again.

An ancient Egyptian Papyrus with incredible astronomical data

An international team of scientists has discovered that an Egyptian papyrus believed to date from around 1244-1163 B.C. it could be the oldest record of Algol’s variable brightness observations, a triple star system known as “the Demon Star.”

The Cairo Calendar. Image credit: Jetsu L. / Porceddu S., doi: 10.1371/journal.pone.0144140.s001.
The Cairo Calendar. Image credit: Jetsu L. / Porceddu S., doi: 10.1371/journal.pone.0144140.s001.

The Papyrus scientists refer to is the so-called Cairo Calendar, also referred to as the Calendar of Lucky and Unlucky Days, and as the name suggests, contained forecasts on all the days of the Egyptian year.

As explained by experts, calendars of lucky and unlucky days, sometimes called hemerologies, occupied a place in ancient Egyptian divination.

Nine primary sources containing full or partial calendars of lucky and unlucky days are
known.

However, it also included observations on the behavior of astronomical objects and, in particular, of Algol.

The Cairo Calendar is divided into three sections (Books I, II and III). Its largest part, Book II, is composed out of 365 passages, one for each day of the 360-day Egyptian year plus five epagomenal days. The passages seem to concern religious feasts, mythological incidents, favorable or adverse days, forecasts, and warnings, say experts.

Algol, the second brightest star in the constellation of Perseus, is a variable star, whose visual magnitude changes with a period of 2.87 days.
Algol, the second brightest star in the constellation of Perseus, is a variable star, whose visual magnitude changes with a period of 2.87 days.

A recent article published in the Open Astronomy, a peer-reviewed, fully open access online journal, shows how the ancient Egyptian scribes presented the celestial phenomena as the activity of the gods.

In particular, the research analyzes how the legends of the Egyptian deities Horus and Set were used in the calendar.

“The discovery of Algol’s variability would have to be dated to thousands of years earlier than has been previously known. The star would have been a part of ancient Egyptian mythology as a form of the god Horus,” said study author Sebastian Porceddu from the University of Helsinki.

The authors of the article believe that the astronomical symbolism discovered suggests that similar clues could be found in other ancient Egyptian texts.

The first ‘modern’ astronomer to notice the variation of Algol’s brightness was the Italian Geminiano Montanari in 1670, while the English John Goodricke measured the star’s cycle in 1782 and suggested partial eclipses of the star by a second body, a hypothesis that was confirmed in 1889.

The third star is at a much greater distance from the other two and does not participate in the eclipses.

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