I know Neil Armstrong placed a mirror on the Moon and people shoot lasers there which get reflected, by this, measuring the time the light is needing, they can conclude the current distance of the Moon. But the Moon is once in a time moving away from the Earth (when annular eclipses are possible) and once in a time getting closer (when total eclipses become possible). Sometimes we hear of records like "the Moon is as close as it wasn't for decades". I remember about one year ago I saw a very close and bright full moon, almost outshining most stars.

So how is it concluded that the Moon would constantly move away from the Earth? Is it just based on the physical prediction of celestial mechanics, like calculation that a day on Earth would get longer and the Moon's orbit slower?

I know Neil Armstrong placed a mirror on the Moon and people shoot lasers there which get reflected, thus measuring the time the light needs they can conclude the current distance of the Moon. But the Moon is periodically moving away from the Earth (when annular eclipses are possible) and getting closer again (when total eclipses become possible). Sometimes we hear of records like "the Moon is as close as it hasn't been for decades". I remember, about one year ago, I saw a very close and bright full Moon, almost outshining most stars.

So how is it concluded that the Moon would constantly move away from the Earth? Is it just based on the physical prediction of celestial mechanics, like calculation that a day on Earth would get longer and the Moon's orbit slower?