The Egyptian papyrus Cairo 86637 calendar is probably the oldest preserved historical document of naked-eye observations of the variability of Algol, or beta (β) Persei. Each day of one Egyptian year was divided into three parts in this calendar. A good or a bad prognosis was assigned for these parts of a day.
“The texts regarding the prognoses are connected to mythological and astronomical events,” says Master of Science Sebastian Porceddu.
A modern period analysis revealed that two statistically significant periods of 29.6 and 2.850 days have been recorded into the good prognoses. The former is clearly the period of the Moon. The second period differs slightly from the period Algol. In this eclipsing binary, the dimmer star partially covers the brighter star with a period of 2.867 days.
“These eclipses last about ten hours and they can be easily observed with unaided eyes. Their period was discovered by the British amateur astronomer John Goodricke in the year 1783,” says docent Lauri Jetsu.“We can explain why the period of Algol has increased by about 0.017 days,” added Lauri Jetsu. “The period increase during the past three millennia could have been caused by the observed mass transfer between the two members of this binary. In fact, this would be the first observation that confirms the period increase of Algol and it also gives an estimate of the mass transfer rate.”
The ancient Egyptians have made accurate measurements that provide useful constraints for modern astronomers.
“It seems that the first observation of a variable star was made 3000 years earlier than was previously thought,” says Lauri Jetsu. “However, I want to emphasise that our research has only been sent to a scientific journal about two weeks ago. This type of results can raise a lot of controversy before they are accepted.”
The research was made in collaboration by the researchers from the Department of Physics and the Department of World Cultures of the University of Helsinki.