[Info-vax] CRTL and RMS vs SSIO

[Lawrence D’Oliveiro]

On Thursday, October 14, 2021 at 7:35:20 PM UTC+13, Phillip Helbig (undress to reply) wrote:
> The leap seconds are added because the rotation rate of the Earth is 
> slowing down ...

Actually it is slowing down on average, but sometimes does speed up. The leap-second system also has provision for _subtracting_ a whole second (so 23:59:58 gets followed by 00:00:00, skipping 23:59:59), if that is ever necessary, which it hasn’t been so far.

> Basically, the tides slow the Earth down. As a result, the 
> Moon recedes from the Earth.

It is the Moon that causes the tides. And the interaction between the tidal pull and the non-uniform density of the Earth that slows down the rotation.

Tides work both ways (as does gravity in general). The Earth’s pull on the Moon caused the same thing to happen to the Moon, only it happened much sooner.

And tides can have some dramatic effects: Io, the Jovian satellite and the most volcanically-active body in the solar system, should have lost all its internal heat a long time ago. But it gets replenished from the tidal action of mighty Jupiter, orchestrated by perturbations from other Jovian moons.

Why does the Moon recede from the Earth? Probably nothing to do with the tides, everything to do with the fact that the Moon does not actually orbit the Earth.

> Thus, the fact that it appears the same 
> size as the Sun is not only a coincidence, but also one that holds now 
> but not in general.

Yes. And also the fact that the Moon is so large compared to the Earth. We are really in a binary-planet system, though for some reason astronomers don’t like that description ...