FIG. 33. A supplement to Fig. 32, with the graphs for Rigel (across C) and Vega (across A), both observed by observers at ground level, but at the same period as Sirius and Arcturus from the ditches.
(1) across sections A and B, viewing at 13.5° in 3638 BC
(2) across sections A and C, viewing at 12.5° in 3447 BC
(3) across sections D and E, viewing at 13.3° in 3624 BC
(4) across sections D and F, viewing at 12.7° in 3512 BC.
Viewing at right angles to far edges:
(5) across sections A and B, viewing at 13.4° in 3677 BC
(6) across sections A and C, viewing at 14.5° in 3395 BC
(7) across sections D and E, viewing at 13.8° in 3677 BC
(8) across sections D and F, viewing at 14.5° in 3514 BC.
In the case of West Kennet it appears that the two different starting points make only about forty years difference to the final results at the head of the barrow, and almost none at the tail. There is a slightly more material difference in the sizes of the derived viewing angles, however. Combining the very limited evidence of the one known ditch section with the height of the mound opposite it, an angle of about 11.9° is obtained for that point. Since some slight settlement and loss of the surface layer can be assumed, any angle between 12° and 14° must be considered acceptable. The height of the observer’s eye is taken as 1.6 m, following the male skeleton sizes at the barrow itself. Even those of smaller stature could be accommodated, for as will be seen from Fig. 31, there was a viewing platform which could have been used by people of all heights above about 1.10 m—so perhaps even children were admitted to the ritual of observing the stars over the barrows. There is some later support for this intimation of democracy, in the ditches at Stonehenge, Woodhenge, Mount Pleasant, and elsewhere.
The later date is here preferred to the earlier. This preference is partly because the later dates fit better with the radiocarbon date (from three specimens of human bone from the barrow, giving a calendar range of 3575 ± 215 BC), and partly it implies marginally smaller viewing angles and a mound of reducing height in relation to the observer.
The head of the barrow seems to be a few years later than the third section. This need not be real, for it must be accepted that our azimuths are subject to error. The results spelled out above are shown graphically in Fig. 32, and broken lines in the neighbourhood of the points representing (1) and (3) are added to show the errors to be expected corresponding to errors in azimuth of half a degree. Roughly speaking, a single error of this amount moves the date by four years. A less superficial analysis might one day therefore easily reverse the order of building these sections.
There are two small residual problems. The year under (2), is obviously entirely spurious, as therefore is the altitude too. It would be interesting to find from future excavation how the altitude was handled in this region. Perhaps levels were changed to preserve the visibility of one star, or to substitute another. One possibility is that section C of the ditch was simply being made to change direction to link up with a section (E) that had already been—or was planned to be—cut with a different orientation from B’s. But why change direction at all? The answer had perhaps something to do with the wish to reduce the barrow’s height, and with the lie of the natural ground making up the tail of the barrow. The last date quoted, however, would seem to indicate that an addition was made to the mound, over a century after the first mound. The only other likely explanation is that viewing angles were not being kept equal, or equal enough.
There is an interesting alternative explanation, that might be extended to preserve the integrity of the entire barrow. Before explaining it, one must consider the way in which the ditches would have been used to observe Arcturus and Sirius. These stars would both have been seen behaving in a very striking and memorable way. At Wessex latitudes Arcturus did not rise and set at all over a level horizon; but here, looking from the southern ditch over the barrow, the star would have dipped down to touch the tomb, seeming to rest there, and then have risen again about half an hour afterwards. Some four and a half hours after that, Sirius would have risen over the tomb, as seen from the northern ditch, and again in much the same time would have sunk back into it at a point not far away.
The two brightest stars were not alone in these comings and goings. Vega would have copied the behaviour of Arcturus very closely, descending into the tomb and rising again, although as seen from the ditch it would have lacked the finesse of Arcturus. In fact the optimum altitude for observing Vega during the period in question (around 3620 BC) would have been a low angle of 7.8°, if the star was to be viewed at right angles to section A, as Arcturus had been viewed. Vega’s visitation would then have begun almost simultaneously with Sirius’ re-emergence.
On what grounds can it be claimed that this additional item of very striking behaviour was in fact observed? Quite simply on the grounds that the angle 7.8° is close to what should be expected—if the mound height conforms to the altitudes found from the ditch—for an observer standing at ground level near the back edge of ditch A.
Having gone so far, did the people of West Kennet leave matters in such an unsymmetrical state? Could they not find a fourth star, in the southern sky, to complete this remarkable pattern? They undoubtedly did so, and the star was Rigel. Rigel, like Sirius, rises only a little way out of the tomb and then quickly falls back in again. On this occasion an altitude of about 7.5° is needed, and this is so similar to the angle from the ground looking north that we know exactly what we must do. We must consider the possibility that equal altitude normal viewing took place from ground level across section A and the aberrant section C. The azimuths taken are 162.4° and 356.5°, and in the usual way an altitude and year are found—7.6° and 3610 BC—at which the arrangement would have been perfect (Fig. 33). It seems probable, therefore, that the ditches will eventually prove to have platforms at the back, at the same level, capable of yielding this common angle.
The anomalous date having been removed, we are now left with a series of dates. Rounding to tens they are (1) 3640, (2) 3610, (3) 3620, and (4) 3510 BC. There is no point in trying to eliminate the spread in the first three dates, in the absence of a more complete excavation. Those dates are so close that for want of better evidence we may take the date of the mound as their mean, 3620 BC. The fourth still seems to indicate a later phase.
The pattern of observing the stellar phenomena was therefore as follows: Arcturus from ditch A, Rigel14 from behind ditch C, Sirius from ditch B, Vega15 from behind ditch A. The seasonal limits during which these phenomena could have been seen vary from star to star, but all three could in principle have been seen on every clear night between roughly a fortnight before the autumnal equinox and a month before the winter solstice. The interval between the mid period of Arcturus’ visit, and the mid period of Vega’s visit the same night, was about six hours.
At this six-hour period, and in this way, the West Kennet people had evidently contrived a series of apparitions, involving four spectacularly well-chosen stars, of a character that might have been interpreted as somehow relating to the spirits of the dead. Only one star visible in Wessex was the equal of any of these four. (Capella was then Vega’s equal—it is now less bright—and both were brighter than Rigel. Canopus, second only to Sirius, never rose at these latitudes, and was unknown.) It would be hard to imagine a simpler monumental design showing more intellectual brilliance than this.
There is, in conclusion, a remote possibility that Sirius might have played a part in the selection of the West