Free money?

 I was playing a game where my bc per turn income was 350. All of a sudden it jumped to like 1800 per turn and stayed that way for half a year or so and then just as suddenly went back to 350. It was very late and I had been playing for a LONG time and was a little blurry-eyed.
 I wasn't building any economy type stuff nor did I take any planets.
 Did I miss some event that skyrockets your income or something? This was the first time I have seen this hapeen