What is the term for the distance varying between Earth and Moon due to the Moon's orbit?

The correct term for the distance varying between Earth and the Moon due to the Moon's orbit is orbital eccentricity. This concept refers to the shape of the Moon's elliptical orbit around Earth, which causes the distance between the two celestial bodies to change over time.

Orbital eccentricity quantifies how much an orbit deviates from being a perfect circle. An eccentricity value of zero indicates a circular orbit, while values closer to one indicate a more elongated (elliptical) orbit. The Moon's orbit is not perfectly circular; therefore, it brings about variations in the distance to Earth, leading to phenomena such as the noticeable changes in the apparent size of the Moon in the sky at different times.

Understanding this concept helps clarify how gravitational interactions and the physical motion of celestial bodies influence their relative positions and distances. This is significant in fields like astronomy and space exploration, as it affects everything from tidal patterns on Earth to satellite positioning and lunar missions.