Timekeeping - a leap second hiatus

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Looks like no leap seconds for a few years - the earth's rotation is speeding up. From Tony Finch:

Leap second hiatus
Normally I only pay attention to leap seconds every 6 months when the IERS publishes Bulletin C, the leap second yes or no announcement. But this week brings news from Michael Deckers via the LEAPSECS mailing list, and it relates to Bulletin A, which is why it’s off my usual 6 month schedule.

Leap seconds exist because the Earth takes (very roughly) about a millisecond more than 24 * 60 * 60 seconds to rotate each day; when we have accumulated enough extra milliseconds, a leap second is inserted into UTC to keep it in sync with the Earth. At the moment the Earth is rotating faster than in recent decades: these shorter days, with a lower length-of-day, means the milliseconds accumulate more slowly, and we get fewer leap seconds.

The news from Bulletin A is not unexpected: in January I noted that we are currently in a long gap between leap seconds, and in July I observed that the length of day chart is still very low.

Bulletin A is a weekly summary of predictions from the latest Earth Orientation model. It includes the projected difference between Earth rotation angle (UT1) and UTC, which in turn determines when a leap second is needed. The notable thing about the latest Bulletin A is the factor 0.00000 in the equation

    UT1-UTC = -0.1746 - 0.00000 (MJD - 59173) - (UT2-UT1)

[ Tangential aside: I feel the need to describe 0.00000 as all balls, because in PostgreSQL you can use “allballs” in a time literal as an alias for midnight :-) ]

The zero factor is multiplied by the date, which is writtem MJD - 59173. This is the time in days after 20th November; the product indicates how much UT1 and UTC are expected to differ in the near future, i.e. the rate of divergence is now zero.

Michael Deckers said in his LEAPSECS message that we haven’t seen a rate difference as low as zero since 1961!

This implies that unless something wild happens, we are very unlikely to have a leap second in the next few years.

And yes, I am a time nerd. I love the technologies used and own an atomic clock (surplussed from the cellular E911 services)

There is a wonderful interview with Dr. Judah Levine - the name might not be familiar but he is our nation's Time Lord:

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This page contains a single entry by DaveH published on November 15, 2020 2:13 PM.

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