The Moon is slowly drifting away from Earth — about 3.8 cm per year
Tidal friction from the Moon's gravity transfers rotational energy from Earth to the Moon, gradually pushing the Moon into a larger orbit. Currently the Moon recedes about 3.8 centimetres per year — confirmed by laser ranging experiments using reflectors left by Apollo missions. When the Moon formed 4.5 billion years ago, it was about 16 times closer to Earth and appeared roughly 16 times larger in the sky. In about 600 million years, the Moon will be too far away for total solar eclipses — it will appear too small to fully cover the Sun.
We experience the Moon as a fixed feature of the sky. Learning it is slowly leaving — measurably, provably, with lasers — and that total solar eclipses are a temporary coincidence of our particular geological moment in time gives the night sky an unexpected transience.
“The Moon is moving away from Earth at 3.8 cm/year, confirmed by Apollo laser reflectors. In 600 million years, it'll be too far for total solar eclipses. We're in a lucky window. 🌕 #OddlyHuman”