This is a very interesting question, and I did a little rummaging to see
what I could find.
I would expect that the Isles of Gaeldom, as in any maritime society,
would have a long important tradition of astronomy for use in navigation.
I came up with a few finds. First is somewhat tangential, an article
called "Cosmology in the Saltair nan Rann", by John Carey, in Celtica XVII
"Saltair nan Rann recounts, in one hundred and sixty-two cantos and
8392 lines, a vast number of canonical and apocryphal tales from the
Old and New Testaments... The rest of the poem is a miscellaneous
assemblage of cosmological lore.
Lines 205-60 are given over to a discussion of the signs of the zodiac.
This material is probably computistic in origin... For lines 261-8 I do not
know the source:
Five things each day, without falsehood
are to be known by every scholar;
by everyone, without semblence of mockery,
who is in holy orders.
The day of the sun's month, the moon's age,
the sea's course without caprice
the day of the week, the feast of the pure saints..."
This also mentions a reference which I have not yet seen: 'An unpublished
Astronomical Treatise by the Monk Diciul', Proceedings of the Royal Irish
Academy 26C. 398.
From "Kate MacDonald: Bean Eairdsidh Raghaill" in Tocher #27 (journal of
the School of Scottish Studies) I saw a song which begins:
"Tha 'Seachdaran air an adhar
'S tha ghealach gun e/irigh fhathast..."
"The Pleiades are in the sky
And the moon has not yet risen..."
From "Occult Elements common to Celtic and Oriental Folklore", by Rev.
Norman MacDonald (in an old Transactions of the Gaelic Society of Inverness)
"The stars are also personified in Celtic lore [as by the Parsee sages].
On a clear night, one can easily find the cluster of six stars called in
Gaelic: 'Nighean Righ Mheangain, a triuir leannan, a cu\, 's a sgalag'
(Daughter of King Meangan, her three lovers, her dog and man-servant)."