Midday on 31st December 2025. The shadow is pointing directly true north, as is the stone. If the shadow was cast on a level surface it would be less than half this length, but this is cast down the northern slope of the platform. This stretches out the shadow and exaggerates the daily changes in the suns height at midday, thereby allowing an easily observed method for telling the day of the winter solstice.
Image credit: Cerrig