3 ms·
According to the Culture timeline (http://theculture.wikia.com/wiki/Timeline http://theculture.wikia.com/wiki/Timeline), the Twin Novae battle occurred in 1367,
by david-given 10y ago
According to the Culture timeline (http://theculture.wikia.com/wiki/Timeline http://theculture.wikia.com/wiki/Timeline), the Twin Novae battle occurred in 1367, and the light reached (er, will reach) Masaq' in 2170.
(The Culture found Earth in 1977, shook their heads sadly, and then went away again.)
So if we're seeing the light now, that means that we're 649 light years from Portisia and Junce, which suggests that Arm One-Six is what we would call the Orion Arm (the one on which our sun is located). Which means that we were right in the middle of the Culture-Idiran war back in the 14th century. Lucky us!