Thanx Kat interesting links. I am not an expert on this topic but know enough not to make big errors.
T in Ok You are confusing a place with a culture - Ireland and the Gaels. It is simply not the case that Ireland is the origin of these people, much less of celtic astronomy. (There is one interesting place in Ireland at Newgrange and it has some interesting features. There is a web page.)
I hope I ain't confusing anyone here. The Gaelic speaking Celts Scoti etc arrived in Britain hence Ireland/Eire long after the other much more numerous branch - The latter occupied Southern England and Wales. The language they used is like modern Welsh or Cwmraig(I hope my spelling is correct my Welsh is so bad grrrr)
These Gaels were unlike the other celts and moved around lots. So you'll find traces in Bavaria, Switzerland and NW Spain for example. Gaelic I believe is a mixture of several ancient languages. The Gael were known for their ability to quickly learn lanuages and absorb them.
I hope that helps to redirect the focus to more likely sources of information.
Some Halloween Stuff
The Greeks made war upon the Keltoi ...were these our wandering Gaels? perhaps, we may never know. I do know that the Greeks complained that the Keltoi would not fight fair after the Greeks had lost a few battles. They reported the Keltoi would run under the (beneath) the legs of the Greek and upend him, then steal his weapons and run away. Funny way of winning battles. Eventualy the Greeks fooled the Keltoi with spooky stuff in the dark - using white robes and candles and making funny sounds. The Keltoi ran away.
Rome once made the Celts mad and were overran all the way to Rome itself, don't recall the exact detail but something to do with spooky stuff. I guess Caesar underestimated em.