Chance of un-intential alignment towards celestial events

When building a structure, it can be that its direction is by chance to an important celestial event; like solstice, lunar standstill limits, etc. It is important to know what the chances are when evaluating structures build without any intentional direction. In that case chance will make that some buildings have un-intentional alignments.


This has been calculated for neolithic buildings like the ones at Loughcrew, Co. Meath, Ireland. In a computer program  (using Monte Carlo analysis) some 9300 passage chambers were build, using the following parameters:
Beside the building dimensions, important information of possible observed celestial event are needed:
The accuracy of the above topocentric declinations is not that important, because the Monte Carlo analysis is not that sensitive to these exact values.

Chance with sky window

Using the above parameters and varying the length of passage+chamber from 0 to 50 [m], the sky window of the buildings is determined. Then averaging this over a lot of these buildings, we get the following picture with regard to the chance of an un-intentonal alignment:
Chance of alignment at Loughcrew type buildings

As an example; when having 10 [m] length passages+chambers with randomly build direction, the chance that it is pointed to a celestial event is 70% when looking at all celestial events (10 solar and 8 lunar) and around 50% when looking at only (10) solar or only (8) lunar events.
So the above gives us an idea of the chance when varying the passage+chamber length, the number of celestial events and using the sky-window method as the area which the celestial object can cross.

Chance with several window types

If we change the methodology of window through:
  1. a sky window (minimum and maximum azimuth and apparent altitude),
  2. the sky window corners (the corners of the sky window with have minimum azimuth&apparent altitude and  maximum azimuth&apparent alttiude)
  3. an azimuth window (no minimum and maximum apparent altitude) or
  4. an average azimuth, the chances changes.
See the following table (the length of passage+chamber is randomly varied between 4 and 12 [m] as lengths seen at Loughcrew cairns):

Solar+Lunar (18)
Lunar (8)
Solar (10)
sky window 76%
sky window corners

azimuth window
average azimuth


Some conclusions from this:

Loughcrew reality

Looking at the actual directions of the 13 passages at Loughcrew (seeing Loughcrew as a region with a relatively closed culture [although evolving!] around 3500 -3000 BCE); they are directed (McMann, [1993]) between 80 and 112°, one around 168° and two around 290°. So 12 of the 13 cairns (92%) will receive possible celestial light during cross quarter and equinox rise/set (6) events, which is much more than the chance (quite small, <0.02%) when they would have been randomly build.
Of course, even though it seems that they could be celestial alignments, the seen directions could also be landscape or ritual alignments.

Disclaimer and Copyright

Last major content related changes: Dec 26, 2003