Observations

Cleopatra, the Dendera Zodiac and the star Sirius

A detail of the Dendera Zodiac

A detail of the Dendera Zodiac displayed at the Louvre, Paris. Courtesy © RMN, Musée du Louvre/ H Lewandowski

Guy asks:

I wonder if someone knowledgeable could comment about the seeming lack of precession by Sirius as viewed at the latitude of Dendera? Is it so? and if so what causes this?

The fact that Sirius seems to maintain its position relative to the position of the sun was a surprise to most scientists (aware of precession), when it was first noticed by the French scientific community following the Egyptian discoveries of Napoleon (and the Dendera Zodiac) in the early 1800’s. Physicist, astronomer, mathematician Jean-Baptiste Biot (21 April 1774 – 3 February 1862) proclaimed that this phenomenon was an oddity of the latitude and horizon around Dendera, meaning it just seemed as if Sirius was immune to the effects of precession.

The Dendera Zodiac was discovered on the ceiling of an ancient temple complex near the town of Dendera in Egypt by Napoleon’s invading army. It shows illustrations of the constellations of the zodiac – the band of stars in front of which the Sun passes during the year – with the illustrations sometimes the same as the western drawings of the constellations and sometimes different. A drawing of it was published in Paris in 1802 and created great interest among the city’s scientists. Most of them assumed that they were looking at a representation of the sky as on a planisphere at a particular date and set out to calculate that date.

Each year the Sun is in particular constellations during the summer and winter solstices and during the spring and autumn equinoxes. These constellations change over periods of thousands of year due to the precession of the equinoxes. This phenomenon in turn is caused by a slow wobble of the Earth’s axis that takes 26,000 years for a complete cycle. As a result every 2000 years or so, the Sun appears to have moved by one zodiac constellation at the time of each equinox and solstice.

Scientists such as Jean-Baptiste Biot took a guess at the location of the equinoxes and solstices depicted on the Dendera Zodiac and then calculated using precession how long ago it was created. A wide results were obtained that were generally many thousands of years in the past. These results were most upsetting to people with religious beliefs as the proposed times for the Zodiac were not in accord with the biblical time scale.

It was in this context that the relation between the solstices and the star Sirius became important. The Ancient Egyptians had two kinds of year: a civil year of 365 days and a year based on the rising of Sirius before sunrise, known as helical rising. The year based on the helical rising of Sirius is approximately 365.25 days. Years based on the helical rising of most stars would vary considerably over thousands of years due to precession, but for Sirius in the period under consideration and observed from the latitudes of Egypt there was little variation. This may explain why the Egyptians chose Sirius to define one of their two years. It is not that Sirius does not move due to precession, but that it happens to move in such a way that the distance between it and the equinoxes remains approximately constant.

Recently, it has been claimed that planets are also shown on the zodiac and their position in relation to constellations has significance as do two eclipses, one of the Sun and one of the Moon that are included. Based on the planet positions and the eclipses the Zodiac has been dated to between 15 June and 15 August in the year 50 before our era. This dating fits in perfectly with a more cultural dating based on empty cartouches, carved boxes usually containing the name of the ruler, that lie on the remaining part of the temple ceiling not taken by the French to put into the Louvre. The empty cartouches suggest that Zodiac was made during the interval between the death of Cleopatra’s father and her ascension to the throne together with her young son with Julius Caesar.

More information
Mystery of an ancient zodiac by Jo Marchant

Egyptian Stars under Paris Skies, Jed Z Buchwald, Engineering and Science (Caltech), Volume 66 No 4 pp20–31 2003

13 responses to “Cleopatra, the Dendera Zodiac and the star Sirius

  • After nearly 200 years of theories and calculations of the age of the Dendera Zodiac, hasn’t anybody thought about make a carbo-14 test and elucidating finally who’s right?

    • Sandra, Yes, it would be great if we could do that but carbon-14 dating only works on organic material, from once-living things. The Dendera Zodiac is a slab of sandstone, and dating when the rock was carved is, of course, the problem.

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  • I think that there are at least two facts that need explanation in this issue.
    The first one is that the current theory of precession, whose author was Newton, can not account for this phenomenon, as was clearly stated by Anthony Cavendish, who insisted that even after the corrections that he had done to the gravitational constant something was wrong with Newton’s theory.
    The second fact is that Biot supposed explanation about the particular geographical location of Denderah as the cause of the non-precession of Sirius is sheer nonsense. It is absolutely impossible that our perspective, from any point of the Earth surface, could change the position of any star, given the distances involved. As regards the relationship between the solar system and the Sirius System, no matter which system is following the other in the stream of the galactic arm, the issue at stake here is that the only movement that could account for the non-precession of Sirius is one that make Sirius to follow precisely, not the movement of the solar system, but rather the idiosyncratic movement of the Earth axis, supposedly caused by the Moon (in lunisolar precession most of the torque comes from the Moon). I wonder if any rational human being can believe that a double system that weights 3,5 solar masses, at 8 light years of distance, could be following this movement of two tiny bodies as our Earth and Moon. Notice also that, as the article Egyptian stars under Paris skies points out in a graph, Sirius mantains until today the same distance from the equinoxes, that is to say that it really does nos preceed.
    So the mistery discovered by the french sages of Napoleon expedition is not at all solved. One of the principal lessons that the history of science teaches us is that coincidences do not exist in a world that is a cosmos, i.e. an ordered whole: so the tuning of the Sirius System with the movement of precession can not be such a coincidence.
    I hope that these remarks may also help.
    best regards JP

  • very interesting. I accidently fell into this stuff about 2 years ago. It’s mind blowing stuff. life changing knowledge. I certainly look at life differently. Loved “lost star of myth and time”. Anyways, I’m glad there’s other people out there like myself.

  • I can answer your question. I have the numbers. They are all inter-related. Sirius is relatively closer, and we follow it. Stars do not move in a straight line around the galactic core, but, rather, in a corkscrewlike or helix fashion. Sirius has a circle ahead of us with a period of 6000 X 260 days. Our own Sun moves in a circle also yet with a period of 25920 X 365.2422 days, that is, 25920 years. Both stars in the same direction move up and away, around the Orion arm, from the galactic center, with a larger period that is due to the Pleiades, the Pleiades of which are up the arm a ways. So of course there are different “precessions” occuring, depending upon the scale of the situation at hand. The 25920 year precession that we know about is actually one of the shorter period ones, due to the Sun’s circular movement, or at least I have described here the equivalent circuit, as show the numbers. And so Sirius in general is moving in the same direction relative to the Sun and in circular fashion, and in general Sirius will tug at the inclinations of the planets. They say this should not be so due to the supposed negligible influence of gravity, yet the numbers show us this may well be so, and so possibly from some other mechanics. We may not have the mechanics, but we do have the numbers.

    • > Oh, small correction to the number 25920, which is the sidereal number. The number relative to Sirius A, Sirius A of which moves in the 6000 X 260 day circle, would be for the Sun a circle of 9360260 days, or near to 25625 years, rather than 25920 years. Both numbers are significant and fit well where it is relevant.

  • Guy Ollivier on the Observatory Facebook page wrote:
    Thanks
    for the reply Nick. I had read Eqyptian Stars under Paris Skies.
    What puzzles me is how the lattitude of the observer can seemingly
    nullify precession of a star, and whether this would apply to all the
    stars that held say the same lattitude
    as Sirius and indeed the opposite lattitude? Does this mean that if a
    star is not on the ecliptic it appears to precess at a slower rate
    (i.e. it transcribes a smaller circle than the ecliptic which is a
    great circle?) or is it simply the result of the angle of viewing
    between the observer’s lattitude and the lattitude of the star? This
    question has caused considerable confusion among a group of people I
    communicate with, some of whom think it is just a matter of poor
    measurements and that the whole idea of Sirius appearing to remain
    approximately constant in distance to the equinoxes while other stars
    do not is a fallacy. I thought perhaps there would be a relatively
    simple explanation of the mechanics of it.

    • Hello Guy. There is no simple explanation and you just have to go through the somewhat messy calculations involved. The situation though is nicely illustrated in the diagram on page 30 of Eqyptian Stars under Paris Skies.

      Precession (P) is simple in ecliptic coordinates – a yearly 50 seconds of arc increase in longitude and no change in latitude. It gets more messy when expressed in right ascension (A) and declination (D).

      Taking the obliquity of the ecliptic, which is about 23.4°, as E, the formulae are

      Yearly change in A = P (cos E + sin E. sin A.tan D)
      Yearly change in D = P. sin E. cos A

      You could try playing around with the values for precession you get as you insert into the formulae varying values of A from 0 to 360° (0 to 24 hours) and values of D from +90° to -90°. Note that Sirius is at right ascension 6 hours 45 minutes and declination -16° 43′.

      The latitude of Dendera only comes into the calculation of the position of Sirius or other stars at the time of their helical rising.

      I hope that this helps

      Nick

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