Arc of Sight of Sirius (Ancient Egypt)
| Sirius in hieroglyphics | ||||
|---|---|---|---|---|
| New kingdom |
Sopdet Spd.t The dangerous goddess |
|||
| Greek | Σωτις ("Sothis"), Σείριος ("Seirios") | |||
The apparent arc of vision of Sirius denotes the minimum distance between the under the horizon standing sun and located on the visible sky star Sirius, which is necessary to heliacal and akronychische to observe up or sunsets. The true arc of vision of Sirius defines the distance between the actual location of Sirius above the horizon and the actual location of the sun below the horizon.
The difference between these two definitions of the visual arcs is about 0.3 ° during the heliacal rise of Sirius. The necessary arc of vision shows a low value for acronymic rising and heliacal setting, since the sun is on the opposite horizon.
Heliac rises and acronyms of Sirius
Besides Canopus, Sirius is the only star that can be seen without the scattered light of the sun during the night, with the exception of twilight , at a horizon height of almost 0 °. Its apparent heliacal rising occurs just under four minutes before the true heliacal rise due to the effects of refraction and extinction .
In practice, the apparent arc of vision is decisive for the sighting of Sirius during his heliacal rise , although Sirius is actually about 0.3 ° lower. In astronomical calculations that refer to the time of the heliacal rising of Sirius, the dates of the true and the apparent arc of vision of Sirius are given.
Classic calculation basis
In earlier times, due to a lack of computer programs and inaccurate calculation values, astronomers defined the actual angle between the sun and Sirius as the arc of vision of Sirius . The values of astronomical refraction, which determines the apparent location by the refraction of light rays from celestial objects, was not yet part of the classical definition.
Hellenistic astronomers used an arc of 11 ° for Sirius in ancient Egypt , which modern astronomy initially adopted and used for calculations. Observations by Ludwig Borchardt and other Egyptologists in Thebes , Asyut , Minia , Cairo and Heliopolis , which were carried out in 1925 and 1926, led Paul Victor Neugebauer to assume that the corresponding arc of vision was in the range of 8.6 ° to 9.4 ° must be reduced.
Northern areas near the Nile Delta were in the upper range, southern Upper Egyptian regions in the lower range. After further revisions, the mean value was 9 °, which now comprised a lower range of 8.3 ° to 8.5 °, with the value 9 ° corresponding to four sun diameters above the horizon . Neugebauer described this value as the "Egyptian arch of normal vision for Sirius early risers".
In 1937, however, Neugebauer published Sirius calculations, which were based on a visual arc of 9.5 °. Neugebauer justified his changed published data with an "adjustment to the traditional data"; He was also convinced that the Sirius staircases that have been handed down were observational values, but without being able to name any evidence.
Visual arc values
Ludwig Borchardt carried out sightings in Cairo and Thebes in 1925 and 1926. To this end, he published the following entries, from which it can be deduced that Sirius appeared over the horizon during his heliacal rise in Thebes in 1926 about 38-40 minutes and in Cairo about 42-44 minutes before sunrise, to after another five to ten minutes to reach the required visibility limit.
“Cairo, August 3, 1925, 4:42 am: Sirius seen safely with the naked eye; it shines white from the red glow of the twilight. Height determined at about 2 °; 5:16 am, the upper edge of the sun emerges sharply above the Mokattam . Thebes, July 30, 1926, 4:37 a.m .: Only the upper stars of Orion are visible. Seeing Sirius for the first time through the reddening, some haze, sparkling; not like a small disc like in the two previous years, but as a sharp point; 5:11 am upper edge of the sun visible. "
| Sirius heliacal rise | ||||||
| year | date | place | Apparent sunrise |
Apparent Sirius sighting |
Apparent arc of sight |
Type of sighting |
|---|---|---|---|---|---|---|
| 1925 |
August 3rd ( 24th Achet III ) |
Cairo | 5:16 am | 4:42 am ( 2.1 ° ) | 9.6 ° | Borchardt |
| 1925 | 30th July | Thebes | 5:11 am | 4:36 am (1.3 °) | 9.3 ° | calculated |
| 1926 | 3rd August | Cairo | 5:16 am | 4:43 am (2.1 °) | 9.4 ° | calculated |
| 1926 | 30th July | Thebes | 5:11 am | 4:37 am ( 1.3 ° ) | 9.1 ° | Borchardt |
| 1927 | 3rd August | Cairo | 5:16 am | 4:43 am (2.1 °) | 9.2 ° | calculated |
| 1927 | 30th July | Thebes | 5:11 am | 4:38 am (1.35 °) | 8.8 ° | calculated |
| 1928 | August 2nd | Cairo | 5:16 am | 4:44 am (2.1 °) | 8.9 ° | calculated |
| 1928 | 30th July | Thebes | 5:11 am | 4:35 am (1.35 °) | 9.5 ° | calculated |
Arch of Sight in Ancient Egypt
Basics
A retransmission of the arc of vision determined by Neugebauer cannot be taken over unchanged to Ancient Egypt, as due to the precession and the proper movement of Sirius, the places of rise ( azimuth ) constantly oscillate. A calculation made uniformly leads to incorrect results. The proper movement of Sirius in the direction of the horizon was a good three moon diameters up to the beginning of the Old Kingdom , which corresponds to about 1.7 ° and meant an upward shift in the constellation of the Great Dog as well as a changed shape of the ancient Egyptian triangular constellation of the Sopdet .
In the case of the sun, the inclination of the ecliptic causes a long-term shift in the rising and setting points or a changing declination . Associated with this, the arc of vision is also subject to long-term fluctuations with regard to the heliacal rising of Sirius. A decrease in the difference between the sun and Sirius necessarily leads to a higher arc of vision, while the arc of vision decreases as the azimuthal difference increases. The sample calculation for Cairo makes these movements clear (cardinal points: N 0 °, NE 45 °, E 90 °, SO 135 °, S 180 °, SW 225 °, W 270 ° and NW 315 °):
| Azimuth of Sirius and Sun (heliacal ascent sighting) | ||||||
| year | date | place | Sun position | Sirius position | difference | annotation |
|---|---|---|---|---|---|---|
| 1925 |
G August 3 J July 21 |
Memphis | 64.4 ° | 110.4 ° | 46 ° | Borchardt |
| 139 | G July 18 J July 19 |
Memphis | 60 ° | 110 ° | 50 ° | calculated |
| 239 BC Chr. | G July 14 J July 18 |
Memphis | 59 ° | 110 ° | 51 ° | calculated |
| 1279 BC Chr. | G July 6 J July 17 |
Memphis | 58 ° | 112 ° | 54 ° | calculated |
| 1909 BC Chr. | G June 30 J July 17 |
Memphis | 57 ° | 113.5 ° | 56.5 ° | calculated |
| 2769 BC Chr. | G 23 June J 16 July |
Memphis | 57 ° | 117 ° | 60 ° | calculated |
The azimuthal distance from Sirius to the Sun , which has been slowly decreasing since the Old Kingdom , initially suggests an increase in the visual arc values. However, the steady increase in the apparent brightness of Sirius speaks against this. In conclusion, this means a lower luminosity of Sirius for the epoch of the Old Kingdom, since Sirius only had an apparent brightness of −1.42 mag at this point in time . Another factor to be taken into account are the changed values of the refraction , which result in individual arc values for each observation site. The earlier climatic conditions mean compared to the present, in turn, a smaller arc of vision for ancient Egypt.
The studies carried out by Ludwig Borchardt in 1925 and 1926 show a north-south divide . In Lower Egypt the arcs of sight were at the upper limit at or above 9 °; in Upper Egypt, however, at or below 8 °. Every change in the visual arc values affects the reaching of the visibility limit with regard to the necessary minute difference between Sirius and sunrise. The average visual arc of 9.5 ° used by Neugebauer means, as a result, a deviation of his dating of at least one to two days for the values of the reference location Memphis chosen by him . Christian Leitz is of the opinion that in ancient Egypt for the Memphis region based on his earlier calculations for the years 1314-1311 BC. An arc of vision of at least 8.6 ° and a maximum of 9.4 ° was necessary, from which he uses an average value of 9.0 ° as the "safe mean" and 1314-1311 BC. Dated the heliacal rising of Sirius to the days of July 18th and 17th (Julian calendar).
Taking into account Borchardt's sighting height of around 2 °. For the Memphis / Cairo region, however, the arc of vision for the years mentioned by Christian Leitz was between 8.3 ° and 7.3 °. The Egyptologist Rolf Krauss sets in accordance with Borchardt's values and taking into account the azimuthal difference for the year 1313 BC. On July 16 (Julian calendar) as the day of the heliacal rising of Sirius in the Memphis region, which corresponds to an arc of sight of 7.4 ° and a sighting of Sirius at 4:21 am; about 11 minutes after reaching the horizon and about 30 minutes before sunrise. These values deviate only minimally from Borchardt's sighting in 1925, as the difference in the arc of sight at that time was an average of 43 minutes.
Observations of the heliacal Sirius rising
In the seventh year of Sesostris III's reign . a lower-ranking temple employee informed the priest reading of the temple of the pyramid city of Sesostris II about the special event 21 days before the heliacal rise of Sirius:
“You should know that the heliacal rising of Sirius takes place on the 16th day of the fourth month of winter . Announce it to the priests of the city of Sechem-Sesostris-maa-cheru and Anubis on the mountain. "
At the same time, the heliacal rising of Sirius was noted in the coffin texts regarding the diagonal star clocks . Christian Leitz and Rolf Krauss therefore consider it likely that at least with the advent of the diagonal star clocks, the rise of Sirius was derived from other star rising and was therefore no longer directly observed. Along with this, there is the possibility that there was no direct connection between the arc of sight and the heliacal Sirius rise since the 12th dynasty . The table lists the actual arcs of vision and dates of all relevant reference regions for the period between the end of the 11th and mid-12th dynasty.
| Arc of vision of Sirius at the heliacal rise (Julian calendar) | ||||||
| year | Alexandria | Cairo | Memphis | Thebes | Elephantine | |
|---|---|---|---|---|---|---|
| 2000 BC Chr. | 7.4 ° (July 17th) | 7.5 ° (July 15) | 7.5 ° (July 15) | 7.9 ° (July 11th) | 7.4 ° (July 9th) | |
| 1830 BC Chr. | 7.4 ° (July 17th / 18th) | 7.4 ° (July 15/16) | 7.5 ° (July 15/16) | 8.0 ° (July 11th / 12th) | 7.6 ° (9/10 July) | |
literature
- Rolf Krauss: Sothis and moon dates: studies on the astronomical and technical chronology of ancient Egypt . Gerstenberg, Hildesheim 1985, ISBN 3-8067-8086-X , pp. 40-45.
- Paul Victor Neugebauer: The changing year and the bound lunar year . In: Astronomical News (261) . Recheninstitut Heidelberg, Heidelberg 1937, pp. 377-378.
Web links
Individual evidence
- ↑ Rolf Krauss: Sothis and moon data: Studies on the astronomical and technical chronology of ancient Egypt . P. 104.
- ↑ Alexandra von Lieven : Wine, Woman and Song - Rituals for the Dangerous Goddess - In: Carola Metzner-Nebelsick: Rituals in Prehistory, Antiquity and the Present - Studies on Near Eastern, Prehistoric and Classical Archeology, Egyptology, Ancient History, Theology and Religious Studies ; Interdisciplinary conference from 1-2. February 2002 at the Free University of Berlin - , Leidorf, Rahden 2003, ISBN 3-89646-434-5 , p. 47.
- ↑ The Mokkatam is a hill near Cairo .
- ↑ a b Ludwig Borchardt observed the so-called apparent sunrise , which occurs about four minutes before the true sunrise . The refraction makes the sun visible before actually reaching the horizon. The difference is around 0.6 °.
- ↑ At the time of the sighting.
- ↑ a b Azimuth: Sun NE 64.5 °, Sirius SE 110.5 ° (azimuth difference 46 °).
- ↑ a b Azimuth: Sun NE 64.5 °, Sirius SE 109.5 ° (azimuth difference 45 °).
- ↑ Christian Leitz: Ancient Egyptian star clocks . Peeters, Leuven 1995, ISBN 90-6831-669-9 , p. 68.
- ↑ a b Rolf Krauss: Sothis and moon data: studies on the astronomical and technical chronology of ancient Egypt . P. 47.
- ↑ Difference between Sirius reaching the horizon height and the later sunrise