Her father was Professor Michael J. O'Kelly, Professor of Archaeology at University College, Cork, who discovered the midwinter illumination of Newgrange in 1967.
The mound's passage is shorter than the long entryways of monuments like Newgrange, which makes it less precise in providing alignments with the Sun; still, Martin Brennan, in The Stones of Time, states that the daily changes in the position of a 13-foot (4-m) long sunbeam are more than adequate to determine specific dates.