I don't understand, how can tidal forces make the orbits more circular? Perhaps it has something to do with the fact that in elliptical orbits (unlike in circular orbits) the velocity is not always perpendicular to the acceleration? Or maybe it does not have to do with the tidal forces from the sun but instead with the tidal forces from the moon? But then we would also need an explanation of why more energy is lost when the Earth is moving faster (which must be the case in order to become more circular, right?). I know nothing about astronomy. Perhaps I'm misunderstanding what "tidal forces" are so I will explain what I think it means. In my understanding, "tidal forces" refers to the effect that the force of gravity tends to stretch large bodies along one direction (parallel to the net force) and compress large bodies in the other (perpendicular) direction. But I can't figure out how this could cause orbits to become more circular over time.