Shadow Casting Phenomena at Newgrange

Abstract

A digital model of the Newgrange passage tomb and surrounding ring of monoliths known as the Great Circle is used to investigate sunrise shadow casting phenomena at the monument. Diurnal variation in shadow directions and lengths are analysed for their potential use in the Bronze Age to indicate the passage of seasonal time. Computer-aided simulations are developed from a photogrammetric survey to accurately show how three of the largest monoliths, located closest to the tomb entrance and archaeologically coded GC1, GC-1 and GC-2, cast their shadows onto the vertical face of the entrance kerbstone, coded K1. The phenomena occur at astronomically interesting declinations, consistent with possible seasonal observance of the rising Sun at key dates in the Bronze Age when the Great Circle was constructed. The analysis further shows how the dominant three-spiral motif on K1 is repeatedly targeted by shadow casting on these dates, making this artistically elaborate motif focal. This could indicate the positioning of GC1, GC-1 and GC-2 enabled users in the prehistoric past to predict and mark seasonally different periods of ceremonial or ritual importance. The investigation further reveals that GC3 casts a shadow onto the base of GC5 on dates which are compatible with the proposed low-precision calendrical model. The cycle of shadow casting is considered to commence and end at winter solstice. Recorded site photography verifies the computer simulations and provides visualisations for archaeological record.

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