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Heliacal rising of Sirius in Thebes

The results which are shown here are given by a personal software working in JavaScript from data found in "Sky Catalogue 2000.0". It enables, for instance, to determine the time when a star becomes visible again in the morning after its period of invisibility (heliacal rising). You can yourself compute the date of this kind of phenomenon with the help of this JavaScript program . Be so kind as to e-mail me if you find bugs in this software.
I far prefer the gregorian calendar but I have added -for the historian's pleasure- the corresponding date of the julian calendar.

Altitude of Sirius = 2

For completion'sake, I will add that, in 1951 BC (-1950), the sun reached the solstitial point on july 24th -Gregorian calendar- which corresponds to july 11th in the julian calendar.
In -1950, the heliacal rising of Sirius should therefore have taken place, in Thebes, four days after the solstice.

The following table describes the heliacal rising of Sirius between -2500 and -1500 at the latitude of Thebes.

The data in relation with the julian calendar are printed in blue. Those about the gregorian calendar are printed in red.
As you can see, the heliacal rising of Sirius is, in the julian calendar, unwedged by only one day in a millenary. This so called fixity must not hide the truth for it's only the result of the added action of two displacements which - it's a perfect hazard - make up for each other.

  1. The displacement of the julian calendar in connection with the seasons (and therefore with the gregorian calendar).
  2. The displacement of the heliacal rising in connection with the solstice owing to the precession of the equinoxes.

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