[time-nuts] New leap second

Poul-Henning Kamp phk at phk.freebsd.dk
Fri Jul 4 19:35:36 EDT 2008


In message <002401c8de00$2a82ca80$021ba8c0 at cyrus>, "Bill Hawkins" writes:

>Well, yes. The Earth expands from the heat, rotation slows, [...]

You're right, but from my back of the envelope calculation, it's
negligble.

Most of the expected expansion is the water in the oceans, which
expand roughly 10^-4 per Kelvin in the relvante temperature range.

When you factor in that the average dept of the oceans is close to
4000m, but not all of it is expected to warm up in our lifetime,
so you get that 1K increased temperature is roughly 0.1 meter sea
level increase.

That means that the radius of the earth increases by about 15 parts
per billion.

But since the density of water is much lower than the rest of the
planet, and that the water amounts to less than a twothousandth of the
radius, the increase in angular momentum is only in the 10^-12 range.

10^-12 of a year is 31.5 microseconds, which would be added to the
UTC-UT1 difference.

Measurable, but not a problem compared what else one Kelvin would
cause of trouble.

Poul-Henning

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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