St Lythans spring sunset at through the porthole

The Spring Equinox happens on Sunday 20th March in 2022, but observations of the setting sun pouring through the west end port-hole are possible between 18th and 22nd, depending on the sun and sky at sunset. Even on a sunny evening, low cloud banks on the horizon can mess up the final moments. I took the video down because we never got around to editing it to be shorter, but its back up now at filiast. com. This year, weather willing, we will try for a more succinct filming.
ArchAstro asks good questions. The Coflein entry (https://coflein.gov.uk/en/site/227289/) gives info of limited excavations and suggest the mound was covered, and the possibility of a shaft begs all sorts of questions about usage and how it was experienced. I have a photo that shows how the light inside hits the stones themselves. One day, we'll go back and do a officially sanctioned equinox watch under a tarp to test out what it would have been like inside, waiting for that 12 seconds of connection with the horizon sunset.