Archaeoastronomy from the Air - The Stones and the Stars: Building Scotland's Newest Megalith - page 264

F IG . 9.5 Part of the long alignment at Brainport Bay (Photo by Duncan
Lunan, 1978)
There are cup-and-ring markings on other nearby rocks, and
off the main axis there's an elliptical cairn whose long axis seemed
to mark midsummer sunset/midwinter sunrise, though it may in
fact be relatively modern. Subsequent investigations found the site
to have a major equinoctial alignment, but it has extra significance.
From that position, the setting Sun would appear only once every
4 years, indicating that the site's creators had discovered the Leap
Year. The original alignment would recur almost exactly after 33
years, and in 1976 a cache of 33 carefully selected white quartz
pebbles was found hidden under a flat stone at the northeast end of
the main alignment [ 4 ] . MacKie's critics accused him of grasping
at straws to justify claiming an important astronomical use for the
site; once again, readers may draw their own conclusions.