Our drifting moon away from the Earth
The Moon is drifting about 1.5 inches (3.8 cm) farther from Earth each year, a slow but measurable change that has been tracked for decades using laser ranging to retroreflectors left on the Moon by astronauts and missions Futura+1.
How It Happens
The primary cause is tidal interactions between Earth and the Moon.
The Moon’s gravity pulls Earth’s oceans into two bulges — one facing the Moon and one on the opposite side ScienceAlert+1.
Because Earth rotates faster than the Moon orbits, these bulges lead the Moon’s position slightly.
This misalignment creates a gravitational tug on the Moon, transferring energy from Earth’s rotation to the Moon’s orbit, pushing it outward Futura+1.
- In turn, Earth’s rotation slows, making our days ever so slightly longer over time.
Measuring the Change
Scientists measure the Moon’s distance by bouncing laser pulses off mirrors on its surface and timing the round trip. This allows them to detect changes as small as a fraction of an inch per year ScienceAlert+1.
Other Effects
Tidal changes: The Moon’s retreat alters ocean tides and their timing.
Day lengthening: Over millions of years, this process has lengthened Earth’s days by several seconds per century Futura.
Orbital variations: The Moon’s orbit is elliptical, so its distance from Earth changes by about 12,400 miles (20,000 km) over a month, creating “supermoons” when it’s closest ScienceAlert+1.
Long-Term Implications
While 1.5 inches per year may seem tiny, over billions of years it has significantly shaped Earth’s rotation and tides. In the distant future, the Moon will be much farther away, and Earth’s days will be longer, potentially affecting climate and ecosystems.
In short, the Moon’s slow retreat is a direct result of the gravitational dance between Earth and its satellite, a process that has been shaping our planet since it it was created.
(My own pics of the moon tuesday morning 7:46:47 am (DST) from my driveway in Zellwood Florida.)
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