If one more member makes a reference to my age........I wasn't looking at the sky back then!I can recommend Excession...
Two and a half millennia ago, the artifact appeared in a remote corner of space, beside a trillion-year-old dying sun from a different universe. It was a perfect black-body sphere, and it did nothing. Then it disappeared. Now it is back...
...An Outside Context Problem was the sort of thing most civilizations encountered just once, and which they tended to encounter rather in the same way a sentence encountered a full stop.