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Re: The Three-body Problem
From: Peter Monta
Date: 2021 Oct 28, 15:57 +0000

... I think the brief answer is no, leap seconds are not influenced by any variation of the orbit of the Earth around the Sun. Leap seconds are purely to keep UTC true to Earth rotation.

I still think this is true, but maybe it's a little more complicated than it first appears. "Earth rotation" here means UT1, and that is derived from the Earth rotation angle (in the nonrotating ICRS). But where does the Sun come in, if it comes in at all? Well, if I'm reading the definition of UT1 correctly, it sort of comes in during the scaling to SI seconds: UT1 = f(ERA). But this mapping f has a fixed, constant, baked-in value for the year! If the actual year were to change somehow (without changing the Earth's angular momentum), UT1 would change not at all, and it (and UTC) would start to drift away from the Sun. That seems odd, but I suppose it means that the year is very predictable, any changes would be very small compared to Earth rotation, and it can be safely baked in.

Cheers,

Peter

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