Sky above the tomb

Tombs in Spain and the Sahara face the low winter sun far more often than chance would have them. Irish tombs do not.

A compass seen from above, prehistoric tombs stacked inward at the directions they face, most on its eastern side, the same tombs turned to random directions in a ring inside it, and the year as two curves under it. Through the year the low sun slides along the horizon. At midwinter it lights a dense fan of south-east-facing dolmens and their curve stands far above chance.

The directions the tombs face are measured: 108 dolmens on the Gor River, 220 Saharan monuments, 172 Irish tombs. The sky is computed for 3000 BCE, and six thousand years move the sunrise by under a degree. Around midwinter the low sun faces 30 percent of the dolmens, against 13 percent with them turned at random, and fewer in summer. Ireland matches chance. Nothing says the builders meant it.

Directions: Cabrero González 2023, Rodríguez-Antón et al. 2023, Archaeological Survey of Ireland (all CC BY 4.0). Sun after Laskar 1986.

Read the paper: Rodríguez-Antón et al. 2023