It has to be noted that the Coptic Calendar New Year date of 11th September in Egypt is only symbolic, as it is attached to the Gregorian Calendar, Sirius in our era doesn't rise with the Sun on this date in Egypt.
So what date does Sirius rise with the Sun in Egypt in our Era?
The Revolution of 1952 in Egypt will tell the answer being 23rd July 1952, it was intended to coincide with Sirius rising with the Sun.
Egyptian Revolution of 1952 - Wikipedia, the free encyclopedia
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