Dr Frank Prendergast on Archaeoastronomy

This presentation was delivered to Space Oddities Live by Dr Frank Prendergast, who discusses the field of archaeoastronomy with particular reference to ancient archaeological sites in Ireland.

Dr Prendergast is a chartered surveyor and archaeoastronomer. He graduated from DIT (now TU Dublin) and completed postgraduate studies at TCD. His PhD, awarded by the School of Archaeology at UCD in 2011, examined the alignment and landscape siting of passage tombs in Ireland and Britain.

His research covers the Neolithic, Bronze Age, and Iron Age, focusing on prehistoric landscapes and monuments through the lenses of cultural astronomy and skyscape archaeology. He is a member of the European Society for Cultural Astronomy, with links to the Sophia Centre at the University of Wales, and is also a member of the International Society for Archaeoastronomy and Astronomy in Culture.

Frank Prendergast on Passage Tomb Alignments

A central point is that passage tomb alignments must be understood in terms of both direction and horizon. It is not enough to say that a passage faces east or west. The height and shape of the skyline determine where and when the sun will appear, and this directly affects whether light can enter the passage.

Newgrange and the Winter Solstice Alignment

Newgrange is presented as the best known example of a passage tomb aligned on a solar event. At sunrise around the winter solstice, light enters the monument through the roof-box above the entrance and travels along the passage to the chamber. This illumination depends on a precise combination of passage orientation, entrance design, and horizon position.

The effect occurs over a small number of days rather than a single instant, reflecting the movement of the sun along the horizon at that time of year. This highlights the importance of considering solar motion over a range, rather than focusing on a single calendar date.

Prendergast treats Newgrange as a case where alignment can be clearly demonstrated, while also stressing the need to examine such claims carefully and in measurable terms.

Orientation and Measurement

A key emphasis of the presentation is the importance of accurate measurement. Passage orientations can be recorded and compared with the known positions of the rising and setting sun at different times of the year. By combining orientation data with horizon profiles, it is possible to assess whether an alignment is likely to be intentional.

This approach avoids relying on general impressions. Instead, it uses measurable relationships between monument, horizon, and solar position.

The Role of the Horizon

Prendergast highlights that the horizon is a critical factor in understanding passage tomb alignments. The point where the sun rises or sets is determined not only by direction, but by the altitude of the skyline. Even a small change in horizon height can shift the position of sunrise or sunset.

As a result, each monument must be considered within its specific landscape setting. The surrounding hills and ridgelines form part of how the alignment works.

Variation Across Passage Tombs

The presentation makes clear that not all passage tombs are aligned in the same way. Some show strong correspondence with solar events, while others do not. This suggests that alignment was an important factor in some cases, but not necessarily a universal rule across all monuments.

Careful analysis is therefore required for each site, rather than assuming a single pattern applies everywhere.

Interpreting the Evidence

Throughout the presentation, Prendergast adopts a cautious approach. He demonstrates that certain alignments, such as those at Newgrange, can be supported by measurement and observation, while avoiding conclusions that go beyond the available evidence.

This method provides a clear framework for studying Irish passage tombs, focusing on what can be tested and observed in the field.