After all, we can teach them about our calendar, but how do we describe+transmit when our calendar began in a way they can measure against in their reference fr

After all, we can teach them about our calendar, but how do we describe+transmit when our calendar began in a way they can measure against in their reference frame, in order to know how to do the math to translate dates back and forth? Could this be done by sharing the distance between objects in space? No clue how accurately we could measure it, but if they could say hey year 0 was when earth was X LY from andromeda, and they can calculate how far they are now, and the rate of expansion, they might be able to calculate when year 0 was?