Julian Cope presents Head Heritage

Well, the last reference I've seen to it was looking through the Ancient Lothian site, on a list of festivals.
http://www.cyberscotia.com/ancient-lothian/leaves/features/calendar-of-festivals.html

I've seen them mentioned elsewhere, though, always without an explanation of the alignment, which must fall on the days given, and so are guessable, to an extent, or fall where old samhuinn or old beltuinn fell, for instance. I wondered why they are "lost" and not commonly mentioned, and what the actual alignments are.