5,000 years after the stone age farmers of Co. Meath built their massive stone passage tombs on the hills of Loughcrew near Oldcastle, the sun still returns twice a year on the equinoxes to illuminate a spectacularly carved stone at the rear of the chamber of Cairn T, the largest passage tomb on Carnbane East. On March 21st 2007, and again on the days around September 21st, the length of day and night are equal and the sun passes directly above the equator, the reasons why stone age man chose to mark this particular occasion and its significance to their way of life or religion remains a mystery.

Shortly after 6.30am on 20th March, the sun clears some hazy clouds on the horizon and in moments its rays will reach inside the short passage of Cairn T, cross the chamber and bathe the elegantly carved rearstone of the back chamber in golden light.

The passage of Cairn T opens almost east, positioned so that it faces the sun and catches its rays shortly after it clears the horizon.

The hilltop is littered with the ruined remains of many satellite tombs, none quite as large or as ornamently carved as Cairn T. Barely visible earlier in the morning twilight, the flood of light picks out their weathered and broken stones.

From inside the gloom of the chamber, there is a clear view of the horizon and on a clear day the Hill of Slane, a few miles from Drogheda, can be seen below the rising sun around the equinox. The sun has just begun to rise from the cloudbank and already the backstone of the chamber is partly illuminated with dazzling light.

The sun rises surprisingly quickly and the light inside the passage and chamber can be blinding when viewed from the relative darkness of the interior, so eyes are instead drawn to the rear chamber and its spectacular carved designs.

Shaped by the stones of the passage sides, the sill stones in the passage and chamber and orthostats at the opening of the rear recess, the vernal equinox sunbeam is shaped slightly differently from that on the autumnal equinox. The place of sunrise also moves along the horizon at its quickest at this time of year and this has prompted specualtion that the carvings were designed to measure this casted sunbeam to determine the day of equinox with great accuracy.

The dark square on the backstone is the shadow of the fixtures on the gates to the passage and a large kerbstone to the right of the opening creates the sloped shadow near the bottom of the sunbeam.

Unlike the winter solstice at Newgrange, the equinox event at Loughcrew is very informal and anyone who makes the cold, hard trek up the hillside before dawn will be rewarded with a few moments inside to view the alignment, if the sun makes a fairly rare appearance of course. Small groups are allowed in for some time before leaving to allow others to witness the event.

Carvings along the passage orthostats are easily viewed at sunrise as the directional light brings the patterns and motifs to life.

Half an hour after sunrise, the full intensity of the sun is now focused on the backstone by the passage and orthostats, illuminating almost its entire surface as seen below.

The full illumination of the backstone is a wonderful sight, for these rare moments the endless questions, theories and frustrations posed by these enigmatic markings can be put aside. Sitting and marvelling at this magnificent feat of engineering, astronomy and determination, the feeling of continuity with the ancestors who lived so long ago is enough.

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