heliacal-rising-of-Sirius

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Heliacal Rising of Sirius

To rise heliacally Sirius must rise "approximately 50 minutes" before the Sun:-

This is the first link where I saw this mentioned:-

The heliacal rising of the star Sirius at El Badari

Since there are 1436 whole minutes in 1 sidereal day (relative to the "fixed" stars),

and 360 degrees in the standard circle, there are:-

1436 / 360 = 3.9888... minutes per degree

Therefore there must be "approximately":-

50 / 3.9888 = 12.5348 degrees (12.5)

Between the Sun and Sirius on the day of its heliacal rising.

12.5 is just slightly greater than the modern degree marker for Nautical twilight

Note on modern terminology that relates to this research:

Civil twilight :- occurs when the Sun is 6 degrees below the horizon

Nautical twilight :- occurs when the Sun is 12 degrees below the horizon

Astronomical twilight :- occurs when the Sun is 18 degrees below the horizon

However from the "approximately 50 minutes" I went on to double and triple check the calculations to be sure for myself what the exact figure was.. The first program I used to do this is called > Star Calc < (for results see spreadsheet further down this page)

The link below, that I found later after much surfing of the web, is a really good resource for the timing of Heliacal rising of Sirius throughout Egyptian his-story / her-story.

The heliacal rising of Sirius on July, the 20th, 139 AD

This is the first date I investigated, which is calculated as a naked eye observation.

It is also mentioned on this page, which goes into a bit more detail about the larger Sirius cycle of 1460 years:-

Sothic_cycle

The date is 20th July 139 AD ( Julian calendar )

Below is an image of the sky above Memphis on that day.

The results of the data detailed in the above graphic, is that Sirius was in the sky 13.04 degrees or 52 minutes before the Sun on the day of its heliacal rising. Which matches the original 50 "approximate" minutes mentioned from the first link on this page.

However I still wasnt satisfied, so I look up Memphis with this program > The Photographer's Ephemeris <

And using the coordinates of Memphis, with its +23 meter Elevation, +2 hours Timezone, Latitude 29.8492 N. and Longitude 31.2550 E. ~ I looked it up in this program :-

> Planetary, Lunar, and Stellar Visibility v. 3.0 <

(using default settings for the star Sirius in "visibility parameters" option)

Result 1 (with Critical Altitude 0.0)

First visibility :- 18th July 139 AD

Which is 2 days before 20th July 139 AD, however I later found by more surfing the web and some reading of the manual, that is its also important to change the Critical Altitude.

"The default value is 0°, crossing the horizon, but it is not likely that any star is visible at the horizon so some higher value, depending upon the magnitude of the star and local conditions, should be used."

from the manual of > Planetary, Lunar, and Stellar Visibility v. 3.0 <

So I started to increase this amount until:-

Result 2 (with Critical Altitude 1.3)

First visibility :- 20th July 139 AD

SInce I had found a match with the historical data, I then went on to confirm more dates, I used the dates from these 4 pages:-

The heliacal rising of Sirius under the reign of Ptolemy III

The heliacal rising of Sirius under the reign of Ptolemy IV

The heliacal rising of Sirius on July, the 20th, 139 AD

The date of foundation of the temple of Hathor at Dendara

The result are shown below:-

In each case I used the relevant Elevation, Timezone, Latitude and Longitude to update the program:-

> Planetary, Lunar, and Stellar Visibility v. 3.0 < with more places (locations).

Using > Star Calc < and > The Photographer's Ephemeris <

for confirming exact Elevation, Timezone, Latitude and Longitude.

Every time I checked the heliacally rising time of Sirius, using Critical Altitude of 1.3

The program matched the data from the 4 website pages (historical dates), and also what I found through Star Calc at the beginning of this investigation.

However the number of INDIVIDUAL average minutes increased,

between Sunrise and the rising time of Sirius,

as Latitude increased by a change of location,

they are listed as follows:-

(see spreadsheet above for more details)

48 minutes for Aswan and Thebes

49 for Dendara

51 for Asyut and Memphis

53 for Alexandria

{ 48 + 48 + 49 + 51 + 51 + 53 }= 300

{ / 6 } = 50 minutes

(OVERALL average)