Sothic cycle
The Sothic cycle or Canicular period is a period of 1,461
Mechanics
The
Discovery
This calendar cycle was well known in antiquity. Censorinus described it in his book De Die Natale, in CE 238, and stated that the cycle had renewed 100 years earlier on the 12th of August. In the ninth century, Syncellus epitomized the Sothic Cycle in the "Old Egyptian Chronicle." Isaac Cullimore, an early Egyptologist and member of the Royal Society, published a discourse on it in 1833 in which he was the first to suggest that Censorinus had fudged the terminus date, and that it was more likely to fall in CE 136. He also computed the likely date of its invention as being around 1600 BCE.
In 1904, seven decades after Cullimore, Eduard Meyer carefully combed known Egyptian inscriptions and written materials to find any mention of the calendar dates when Sirius rose at dawn. He found six of them, on which the dates of much of conventional Egyptian chronology are based. A heliacal rise of Sirius was recorded by Censorinus as having happened on the Egyptian New Year's Day between 139 CE and 142 CE.[3]
The record itself actually refers to 21 July 140 CE, but astronomical calculation definitely dates the heliacal rising at 20 July 139 CE, Julian. This correlates the Egyptian calendar to the
To calculate a date astronomically, one also needs to know the place of observation, since the latitude of the observation changes the day when the heliacal rising of Sirius can be seen, and mislocating an observation can potentially throw off the resulting chronology by several decades.
Meyer concluded that the Egyptian civil calendar was created in 4241 BCE.[5][6] Recent scholarship, however, has discredited that claim. Most scholars either move the observation upon which he based this forward by one cycle of Sirius, to 19 July 2781 BCE, or reject the assumption that the document on which Meyer relied indicates a rise of Sirius at all.[7]: 52
Chronological interpretation
Three specific observations of the heliacal rise of Sirius are extremely important for Egyptian chronology. The first is the aforementioned ivory tablet from the reign of Djer which supposedly indicates the beginning of a Sothic cycle, the rising of Sirius on the same day as the new year. If this does indicate the beginning of a Sothic cycle, it must date to about 17 July 2773 BCE.[7]: 51 However, this date is too late for Djer's reign, so many scholars believe that it indicates a correlation between the rising of Sirius and the Egyptian lunar calendar, instead of the solar Egyptian civil calendar, which would render the tablet essentially devoid of chronological value.[7]: 52
Gautschy et al. (2017) claimed that a newly discovered Sothis date from the Old Kingdom and a subsequent astronomic study confirms the Sothic cycle model.[8]
The second observation is clearly a reference to a heliacal rising, and is believed to date to the seventh year of
The third observation was in the reign of Amenhotep I, and, assuming it was made in Thebes, dates his reign between 1525 and 1504 BCE. If made in Memphis, Heliopolis, or some other Delta site instead, as a minority of scholars still argue, the entire chronology of the 18th Dynasty needs to be extended some 20 years.[7]: 202
Observational procedure and precession
The Sothic cycle is a specific example of two cycles of differing length interacting to cycle together, here called a tertiary cycle. This is mathematically defined by the formula or half the harmonic mean. In the case of the Sothic cycle the two cycles are the Egyptian civil year and the Sothic year.
The Sothic year is the length of time for the star Sirius to visually return to the same position in relation to the sun. Star years measured in this way vary due to axial precession,[9] the movement of the Earth's axis in relation to the sun.
The length of time for a star to make a yearly path can be marked when it rises to a defined altitude above a local horizon at the time of sunrise. This altitude does not have to be the altitude of first possible visibility, nor the exact position observed. Throughout the year the star will rise to whatever altitude was chosen near the horizon approximately four minutes earlier each successive sunrise. Eventually the star will return to the same relative location at sunrise, regardless of the altitude chosen. This length of time can be called an observational year. Stars that reside close to the ecliptic or the ecliptic meridian will – on average – exhibit observational years close to the sidereal year of 365.2564 days. The ecliptic and the meridian cut the sky into four quadrants. The axis of the earth wobbles around slowly moving the observer and changing the observation of the event. If the axis swings the observer closer to the event its observational year will be shortened. Likewise, the observational year can be lengthened when the axis swings away from the observer. This depends upon which quadrant of the sky the phenomenon is observed.
The Sothic year is remarkable because its average duration happened to have been nearly exactly 365.25 days, in the early 4th millennium BCE[10] before the unification of Egypt. The slow rate of change from this value is also of note. If observations and records could have been maintained during predynastic times the Sothic rise would optimally return to the same calendar day after 1461 calendar years. This value would drop to about 1456 calendar years by the Middle Kingdom. The value 1461 could also be maintained if the date of the Sothic rise were artificially maintained by moving the feast in celebration of this event one day every fourth year instead of rarely adjusting it according to observation.
It has been noticed, and the Sothic cycle confirms, that Sirius does not move retrograde across the sky, like other stars, a phenomenon widely known as the
- Sirius remains about the same distance from the equinoxes – and so from the solstices – throughout these many centuries, despite precession. — J.Z. Buchwald (2003)[11]
For the same reason, the heliacal rising or zenith of Sirius does not slip through the calendar at the precession rate of about one day per 71.6 years as other stars do, but much slower.[12] This remarkable stability within the solar year may be one reason that the Egyptians used it as a basis for their calendar. The coincidence of a heliacal rising of Sirius and the New Year reported by Censorinus occurred about 20 July, that is a month after the summer solstice.
Problems and criticisms
Determining the date of a heliacal rise of Sirius has been shown to be difficult, especially considering the need to know the exact latitude of the observation.[3] Another problem is that because the Egyptian calendar loses one day every four years, a heliacal rise will take place on the same day for four years in a row, and any observation of that rise can date to any of those four years, making the observation imprecise.[3]
A number of criticisms have been levelled against the reliability of dating by the Sothic cycle. Some are serious enough to be considered problematic. Firstly, none of the astronomical observations have dates that mention the specific pharaoh in whose reign they were observed, forcing Egyptologists to supply that information on the basis of a certain amount of informed speculation. Secondly, there is no information regarding the nature of the civil calendar throughout the course of Egyptian history, forcing Egyptologists to assume that it existed unchanged for thousands of years; the Egyptians would only have needed to carry out one calendar reform in a few thousand years for these calculations to be worthless. Other criticisms are not considered as problematic, e.g. there is no extant mention of the Sothic cycle in ancient Egyptian writing, which may simply be a result of it either being so obvious to Egyptians that it didn't merit mention, or to relevant texts being destroyed over time or still awaiting discovery.
Some have recently claimed that the
See also
Notes
- ^ The date slowly varies within the Gregorian calendar, moving about three days later every four centuries. It presently occurs around the beginning of August.
References
- ^ a b "Ancient Egyptian Civil Calendar", La Via, retrieved 8 February 2017.
- ^ a b Tetley (2014), p. 42.
- ^ .
- ^ a b Tetley, M. Christine (2014). The Reconstructed Chronology of the Egyptian Kings. Vol. I. p. 43. Archived from the original on 2017-02-11.
- ^ Meyer, Eduard, Aegyptische Chronologie, Berlin, Verlag der Königliche Akadamie der Wissenschaften (1904), Ch. I, p.41
- ^ Breasted, James Henry, A History of the Ancient Egyptians, New York, Charles Scribner's Sons (1908), Ch. II, p.15 ("[T]he calendar year of 365 days was introduced in 4241 B.C., the earliest fixed date in the history of the world as known to us."), citing Meyer.
- ^ a b c d Grimal, Nicolas (1988). A History of Ancient Egypt. Librairie Arthéme Fayard.
- ISSN 1874-1657. Retrieved 2021-01-24.
- S2CID 192288579.
- ^ SkyCharts III[full citation needed]
- ^ Buchwald, Jed Z. (2003). "Egyptian stars under Paris skies" (PDF). Engineering and Science. Caltech. Vol. 66, no. 4. Pasadena, CA: California Institute of Technology. pp. 20–31.
- ^ One day per 120 years, see Winlock, H. (1940). "Origin of the Ancient Egyptian calendar". Proceedings of the American Philosophical Society. 83: 447–464.
- ISBN 978-1118718162.
- S2CID 161410518.
- ^ James, Peter (1991). Centuries of Darkness. London, UK.
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: CS1 maint: location missing publisher (link)
External links
- Encyclopædia Britannica (11th ed.). 1911. .