I don’t know the history of the term or its relationship to Copernicus, but I can say how my forgotten source defined it. Suppose you want to ask, “How long will my car run?” Suppose it’s a weird car that has a different engine and manufacturer than other cars, so those cars aren’t much help. One place you could start is with how long it’s currently be running for. This is based on the prior that you’re observing it on average halfway through its life. If it’s been running for 6 months so far, you would guess 1 year. There surely exists a more rigorous definition than this, but that’s the gist.
I don’t know the history of the term or its relationship to Copernicus, but I can say how my forgotten source defined it. Suppose you want to ask, “How long will my car run?” Suppose it’s a weird car that has a different engine and manufacturer than other cars, so those cars aren’t much help. One place you could start is with how long it’s currently be running for. This is based on the prior that you’re observing it on average halfway through its life. If it’s been running for 6 months so far, you would guess 1 year. There surely exists a more rigorous definition than this, but that’s the gist.