THE ANTIQUITY OF THE EGYPTIAN ASTRONOMICAL DECANS Michael G. Reade, D.S.C. IT IS generally supposed that the decans represent stars, probably ones chosen to mark the hours of the night by their risings. The indications are that a full set of decans comprises 36 stars, even if this does imply that the day and the night should have been divided into 36 equal parts instead of 24. Insofar as there is an orthodox explanation for this total number of decans, it is that stars were chosen which differed in their heliacal risings by 10 days, 10 days being the length of the official week at the time when the original selection of stars was made. If the year was 360 days long, there would then have been exactly one year between consecutive heliacal risings of the same star (subject to a variety of additional explanations as to how the system was, or might have been, modified to accommodate the epagomenal days). The snag about division of the day into to 36 parts instead of 24 can be overcome by supposing that "night hours" were much shorter than "day hours" and that night was deemed to be only eight modern hours or 12 decans long. This would imply that at the equinoxes, for instance, "night" officially started about two hours after sunset and ended about two hours before sunrise. The present writer finds the whole of this explanation artificial and unreal; moreover it hardly touches on the question of how, when and why the Egyptians introduced the seasonal hour system, which reckoned long night hours in winter and short night hours in summer. It may not yet be practicable to substitute an alternative explanation which is complete in every respect but some progress towards one can perhaps be made. The principal sources of lists of decans are the coffin lids from Asyut (10th - 12th Dynasties) and the astronomical ceilings (18th - 19th Dynasties, supplemented by later versions, down to and including Roman times; some water clocks and other ancillary objects can also be marked with decans). Excellent summaries of the various decan lists have been assembled by O. Neugebauer and R. A. Parker in their monumental work "Egyptian Astronomical Texts" (Brown University Press, three volumes, published between 1960 and 1969). Partial summaries are also included in many other Egyptological works; particularly recommended are the publications by A. Pogo in the magazines "Isis" and "Osiris" between 1930 and 1936. When studying almost any commentary on the decans, however, it is advisable always to keep checking back with the original lists, as no commentator seem to be entirely free of questionable assumptions as to what was scribal error and what was significant anomaly in any particular list; deemed errors by scribes sometimes even go completely unacknowledged. Whether the decan were already recognised in Old Kingdom times (6th Dynasty and earlier) is not entirely clear from the principal written material of that era which survives and has been published ("the pyramid texts") but it is at least not inconceivable. For quick reference on this subject by English speaking readers, the papers by Drs. H. Chatley and R. Eisler, published in Journal of Egyptian Archaeology, Vol, 26, 1940, pp. 120-126 and Vol. 27, 1941, pp. 149-152, can be recommended. The present writer considers it certain that the decans were already recognised in Old Kingdom times and that this hypothesis can be proved, irrespective of whether the extant records of that era mention them or not. The proof lies in the strange behaviour of individual decans . A few decans change the order of their appearance in individual lists, but only a few, and these decans have something in common. The possible causes of such changes of order appear to be (a) scribal errors, (b) the precession of the equinoxes, and (c) an inversion of the world's axis. Re (b), the precession of the equinoxes is far from sufficient to explain the examples examined in detail below, though it has on occasion been invoked by other commentators to explain inversions of star order (e.g. by A. Pogo); this explanation could only apply to a few rather specialised cases, deriving from decan lists which are dated a minimum of several hundred years apart. Re (c), the interesting thing about an inversion of the world's axis, if accompanied by a reversal of the direction of rotation of the earth (as seems very probable), is that it does not change the order of rising of the stars and so should not change the order of the decans. Those decans which do change their order in the lists are those which are susceptible to apparent change rather than actual change. The Orion decans present an excellent example. Fig. 1 shows Orion as it appears when on the meridian as Thebes (25° 42' N. latitude) at the present day; it should not have looked very different in 2500 B.C., the only significant difference being that it would be rather lower in the sky. The maximum height above the Theban horizon reached by the centre star of Orion's belt (epsilon Orionis) is 63°, at the present day but it would only have been 50° in 2500 B.C. (by retrospective calculation which, though not absolutely reliable, is unlikely to be grossly out in this respect). Should the world be upside down in 2500 B.C., however, Orion would appear as in Fig. 2 when on the Meridian and its height above the horizon would be 79° in place of 50° (also by retrospective calculation). The long arrow at the top of each diagram shows the direction of movement of the constellation as a whole across the sky, on the assumption that an upside-down presentation will be accompanied by a reversal of the direction of rotation of the earth. Note that the order of rising of the stars is not affected. Betelgeuse is the last star (apart from Sirius) to rise in both cases (for an equatorial or near-equatorial observer; the order of rising of the stars of Orion can become changed for observers in differing latitudes). The decans which change the order of their appearance are principally two, usually designated rmn hry sah and rmn hry sah, commonly translated as "upper shoulder (or arm) of Orion" and "lower shoulder (or arm) of Orion". It can probably be agreed that there is not much chance of confusion as to which stars were meant by these descriptions. Orion's upper shoulder is clearly on the observer's left in Fig. 1 but on his right in Fig. 2, so that these decans do change their relative positions in the sky when the world turns upside down. Note, however, that they do not change the order of their risings which is always lower shoulder, upper shoulder, Sirius, even though the shoulders are represented by quite different stars in the two presentations. The two presentations may look remarkably similar but a very little study of the detail of the diagrams will suffice to show that the similarity is more apparent than real. It would seem that the ancient records which were consulted by the ceiling designers must have been based, at least to some extent, on the descriptive parts of the names of the decans ("upper", "lower", "before", ''after", etc.) and not wholly on their order of rising, otherwise there could never have been any doubt that Sirius was always to be found on the side of Orion which was marked by his "upper shoulder" (which would be his left shoulder in one presentation but his right shoulder in the other). Both the Senmut and the Rameses II ceilings place Sirius on the "upper shoulder" side of Orion (from their decanal lists, rather than from their depictions), which we find to be correct; the decan list on the Seti ceiling presents the opposite and "unnatural" alignment (i.e. Sirius on the "lower shoulder" side of Orion). This comment is incidentally equally applicable to both of the principal Seti I astronomical monuments, only one of which - the Luxor one - follows the same general pattern as the Senmut and the Rameses II ceilings; other comments in the present article tend to apply only to this ceiling, which was also the only Seti monument discussed by Pogo. Note, however, that the Senmut and the Ramesseum "general arrangement" depictions present Sirius on the "wrong" side of Orion (as is explained in detail in the author's Senmut & Phaeton article published in SISR Vol. II, No. 1, pp. 10-18, 1977) whilst the Seti "general arrangement" depiction places Sirius on the "correct" side of Orion (as is approvingly noted by Pogo). The basic reasons for this complex mixture of "right" and "wrong" features in the presentation of Orion and Sirius are included on p.15 of the above-mentioned article but they need not concern us here (principally a lack of appreciation by Senmut and his peers that left and right are automatically interchanged in the sky when the world turns upside down and that comets can appear to all earth-bound observer to be travelling tail first. The principal conclusion of the present article is that it would only have been possible to write down a description which would produce the effects we actually see on the astronomical ceilings if the Orion and Sirius decans were already known in 2500 B.C. or thereabouts (with the corollary that they must already have been known at a time when the world was "upside down" and so would quite probably have been originally selected to suit the peculiarities of an upside-down universe rather than a right-side-up one). [*!* Image] [POST-PHAETON. PRE-PHAETON. Aspects of Orion when on the meridian. B=Betelgeuse, S=Sirius. R=Rigel]. It is also worth noting that the principal clutter of faint stars in the constellation of Orion is to be found on the same side of his belt as his sword. Both the Senmut and the Ramesseum ceilings incorporate a crude diagram of the Orion constellation, on which is included a number of small circles in the area between his belt and his upper shoulders. This diagram offers a further inclination that these ceilings were intended to portray an upside-down (Fig. 2) presentation of Orion. This diagram was omitted from the Seti and most other such ceilings. It should perhaps also be added that it seems to the writer a near certainty that the ceilings commemorate an incident which ante-dated their construction by some 1000-2000 years, hence the choice of 2500 B.C. as a possible approximate date for the most recent inversion of the earth; it is also fairly generally agreed that the period 2600-2150 B.C. embraces the era when the presently visible constellations were first listed and named (1). It was commented earlier that the original monuments should preferably always be consulted when any evaluation of the decans is being attempted and this comment is just as applicable to the present article as to any other. The arguments already presented may appear sufficiently complex without the introduction of still more qualifications but the way in which the decan 'ryt ("the star Arit") wanders in and out of the constellation of Orion is but one of the anomalies which has not so far been mentioned here; no adequate explanation for this behaviour appears yet to have been advanced, but there must be one. In other parts of the celestial sphere, the Senmut decan list reverses the expected order of two of the knmt (Kenmut) decans whilst the Seti decan list reverses the expected order of two of the smd (Semt) decans, also two of the hnt(w) decans according to Neugebauer and Parker, though this last appears to be questionable. Previous commentators, when they have noticed these inversions at all, have confidently dismissed them as scribal errors. It seems likely that all of the potential anomalies in these decan lists will not as yet have been picked up, to an extent that there is still plenty of scope for further study of this whole subject of decan identification and order of presentation. The present writer certainly queries whether the correct total number of decans was always 36, for instance, and he expects that it will eventually be shown that the "correct total" is more like 24 to 28, thus permitting a co-relation of "hour stars" with positions of the moon (also a near automatic derivation of the seasonal hour system), but this possibility must remain distinctly speculative for the present. Certainly the possibilities of catastrophism, with one or more inversions of the world's axis, open up new lines of approach which can revolutionise our understanding of these extremely ancient texts, even to an extent of explaining away the apparent regularity of the 36 decan totals on the Asyut coffin lids of the 10th - 12th Dynasties. --------------------- References: 1. Calculations of the era when the constellations were first listed and named have been presented by the following: * R. A. Proctor, "Myths and Marvels of Astronomy", Longmans Green & Co., 1903. * J. Ellard Gore, "Astronomical Curiosities", Chatto & Windus, 1909. * M. W. Ovenden, Journal of the Royal Philosophical Society of Glasgow, Vol. 3, No. 1, January 1966. * A. E. Roy, lecture to this Society in London on 19th November, 1978. _________________________________________________________________ \cdrom\pubs\journals\workshop\vol0202\02egypt.htm