sunniness = sum of days that the sun light is on a defined surface divided by the periodicy [days] of the sun.The smaller the sunniness is, the less days the sun shines on the defined surface and thus the chance that the building could have been deliberately designed to let the light in, is bigger. If the sunniness is zero, no light comes in and then there is a small probability for an alignment!
(remark: 'sun' can be replaced by 'moon' [mooniness] or any other planet/star)
Some examples (measured and calculated):
|Building||Sunniness (meas.)||Sunniness (cal.)||Sunniness
|Maeshowe (winter solstice)||19%, 68 [days]||17%, 62 [days]||53%|
|Maeshowe (Megalithic Month)||1.1%, 4 [days]||1.9%, 7 [days]||53%|
|Newgrange||2.7%, 10 [days]||13.4%, 48 [days]||54%|
|Treasury of Atreus||N.A. yet||24%, 88 [days]
19%, 70 [days]*
|Cairn T, Loughcrew||N.A. yet||23%, 85 [days]||81%|
|Dutch passage mounds***||N.A. yet||30%, 110 [days]||23%|
|Knowth, western passage||
* Calculated with SkyMap.
**A standard room is 4 by 4 [m] and 2 [m] high, it has a window of 1 by 1 [m], a horizon of 0o, the same direction and latitude as the building and using the whole back wall as defined surface.
*** The Dutch passage mounds have a short passage (around 1.5 m), so that is why sunniness of standard room is smaller than of the passage!
Any comments are welcome to my ideas.