Eire 90
Image by Meic

I read the first paragraph of the the story of Da Derga Hostel and the first thing I thought of was comets.

Could be that the Hostel was an observatory and that what is being described is a comet, something similar to the thesis in the book The Celtic Gods; comets in Irish Mythology.
http://www.amazon.com/Celtic-Gods-Comets-Irish-Mythology/dp/0752434446