Shrough Passage Tomb, Astronomically aligned to the Equinox?

The setting-sun within the passage on the Autumn Equinox 2014

Situated on Slievenamuck which makes up one half of the Glen of Aherlow is Tipperary's only confirmed passage tomb. However I do think there are at least two other passage tombs in Tipp, one on top of the Mahurslieve near Kilcommon and another on top of Slievenamon.

This passage tomb is described on Archaeology.ie as follows;

"On the summit of Shrough Hill, part of the Slievenamuck/Moanour mountains, with forestry encroaching to within 10m to N, E and W, forestry to W has been felled affording an extensive view of the Galty mountains and foothills below. A stone wall runs E-W along the S edge of the mound. The monument consists of a roughly circular cairn (diam. 30m; H 2m) with a small, roofless polyogonal chamber (int. dims. L 2.2m; Wth 1.2m), aligned roughly E-W, near the centre of the cairn (De Valera and Ó Nualláin 1982, 101; Ó Nualláin and Cody 1987, 76-8). The sidestones vary in height from 1.2m to 1.8m (ibid. 76). The cairn is overgrown with gorse, heather and low scrub."


Now most people are familiar with the Winter Solstice sunrise alignment at Newgrange in Co. Meath, on the shortest day of the year the rising sun shines into the long passage there. However there are likely to be a number of other intentionally aligned megalithic monuments around Ireland. This is something I have always had an interest in and I created a blog / website about this here. In it I have detailed almost 100 potential alignments around the country.

My trusted companion at Shrough passage tomb.

Here at Shrough the short passage is aligned on an east-west axis with the entrance to the west. I have always suspected that it might be aligned to the setting sun on the Equinox (the day when night and day are half and half) which occurs twice during a year, first in Spring on the 21st March and then in the Autumn on the 21st September.
I previously visited this tomb at the Autumn Equinox sun-set in 2013 but unfortunately the sun was obscured by cloud. Access for the Equinox is difficult as its a bit hairy getting back down out of there after sunset as you are left 2kms from the nearest road on top of a mountain with much forestry all around. I again visited in 2014 and for a few brief minutes the sun broke through a bank of cloud to illuminate the passage. To the west where the sun sets is Knockfierna or "The fairy hill of Donn Firinne" and to the east Slievenamon or "Mountain of women" is clearly in view so this is an area steeped in folklore.
Now I have to accept that as the passage is only 2.2m long and the exact size of the original entrance unknown, this means the alignment lacks accuracy. It is likely that the sun illuminates into the tomb from a good few weeks either side of the Equinox. One thing that would be interesting to see is the exact final setting place of the sun, the last time there I could not see this due to the cloud. If it both illuminated the chamber and set over the hill of Knockfierna on the Equinox then that would greatly reduce the chance of it being a coincidence.

The tomb looking towards the west with an arrow showing where Knockfeerina is located.

The hill of Slievenamuck also appears in folklore on duchas.ie

http://www.duchas.ie/en/cbes/4922302/4868451

"A long, long time ago there lived a fierce black pig on the Sliab na Muc Hills. This pig was the terror of the neighbourhood and nobody would dream of roaming on the hilltops for fear of meeting with this terrible beast. It happened that one day a great giant called Diarmuid chanced to come across the pig at a point or peak on those hills called Corrin (Cairn). The pig in its rage started rooting up the ground and continued doing so until it had made a huge deep hole. This hole is still to be seen and for years everybody that passed it by threw a stone into it, why I cannot say.
The giant then attacked the pig put could not kill it. The battle raged for hours and towards sunset they found themselves 3 or 4 miles further east at a place called Rathdarby. The giant here made a last attempt with his spear to kill the pig but he missed his thrust only to find the pig taking a sudden hold of him on the ground. It then seized the giant by the throat and killed him. He was buried on the spot where today three large stones mark the site of his grave. This grave is on Mr. T. Kennedys land Rathdarby, a few miles from here.
All the old people called the valley lying south of the Sliab na Muc Hills the "Valley of the Black Pig".

This story would have been particularly interesting if the pig had travelled west rather than east. Shrough is 3 or 4 miles from Rathdarby and the mention of sunset in folklore would have been a suggestive one.