The stones show the point on the horizon where the sun rises on the autumnal blot. The distance between the stones is 13 m.
The animation shows the autumnal blot based on the autumnal equinox as defined by 1) Height Model Equinox and 2) Refraction Equinox. See definitions in Days-of-the-calendar.
The gradients of the top of the higher stone is in alignment with the sun’s path.
The sun’s path is exactly right a half moon cycle after the autumnal equinox, defined as the day before autumnal equinox according to today’s definition (“refraction equinox”).
The sunrise on the autumnal blot can be seen today. The next date on which this will occur is October 9 2015, 8:45.