冬至
Each of the three main megalith sites have significant archaeoastronomical significance. Newgrange and Dowth have Winter solstice solar alignments, while Knowth is oriented towards the spring and autumn Equinox. In addition, the immediate environs of the main sites have been investigated for other possible alignments. The layout and design of the Brú na Bóinne complex across the valley has also been studied for astronomical significance.