The answer first
Earth’s rotation carries tidal bulges ahead of the Moon. Their gravity transfers angular momentum from Earth’s spin into the lunar orbit, so Earth slows and the Moon recedes.
Lunar laser ranging measures the present recession at about 3.8 centimeters per year. Extrapolation is not perfectly linear because oceans and continents change tidal dissipation.
The idea that changes the view
Every total eclipse happens inside a temporary geometric era.
What most explanations leave out
The current recession rate cannot be projected unchanged across all geologic time.
Evidence and named signals
- Apollo retroreflectors enable millimeter-scale ranging.
- Geologic tidal records show shorter ancient days.
- Angular-size geometry controls total eclipses.
What remains uncertain
The often-quoted final-eclipse date is an order-of-magnitude forecast, not a scheduled last event.
Why it matters—or what you can observe
The sky’s most familiar alignment is a transient consequence of orbital evolution.
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Open the video companionFurther reading and primary sources
- NASA lunar laser rangingSource checked 2026-07-16
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