jO_77,

My point is that there is no evidence for a single "celtic astronomy" or "celtic calendar" in historical times before the introduction of Christianity and its calendar. I have glanced at the alpes-net web site kat has provided, and I find that the author there is simply assuming the existence of a "celtic calendar" and "celtic astronomy", then generalizing data for the Gauls to the inhabitants of all Celtic-ruled lands. Even so he has to work to fit the Irish cross-quarter days into his scheme, thereby implicitly recognizing that the Irish system of cross-quarter days and the lunisolar system of the Coligny calendar don't fit at first glance.

I'm not aware of any certain chronology for the first installation of a celtic-speaking aristocracy in any part of the British Isles. The only constraint is that, by the time written records begin, the British Isles and other parts of western Europe are ruled by celic-speaking warrior aristocracies. (To keep it simple I'm leaving out the Galatians and other eastern Celts. I think it's true, though, that some of the Eastward conquests are historically documented). The users, or some users, of the so-called La-Tene culture are thought to have been celtic-speaking, but the spread of artistic styles doesn't necessarily coincide with the spread of new linguistic aristocracies. A celtic-speaking aristocracy might have installed itself in Ireland simultaneously with the arrival of the La-Tene styles, or Ireland might have been Irish-ruled before the adoption of the new artistic styles. Nor was the La-Tene culture pan-celtic, even if all its users were celtic-speaking or celtic-ruled: as I understand, the so-called Celtiberians in what is now Spain didn't adopt the La-Tene styles.

This doesn't mean that there were no common cultural elements among the inhabitants of celtic-ruled lands. It doesn't mean that there was no common "celtic calendar". Only that the evidence is sparse and fragmentary, and tends, if any way at all, against the asumption that the Coligny calendar, or any other single calendar, was the common calendar of the British Isles and Gaul.

The human experience of calendrical systems, for what it's worth, also would argue against a single calendar for such a large, diverse, politically fragmented area, in the absence of positive evidence of deliberate harmonization. The modern Jewish calendar seems to have taken centuries to work out. The Roman calendar was theoretically reformed by Julius Caesar, but it took decades to implement correctly. In late 6th century Ireland, the north's system for calculating Easter differed from the south's. Getting a uniform calendar takes a strong commitment to agreement by all parties involved, and even then can take a long time.