On 2026-07-25 04:34 PM, Michael H Deckers via tz wrote:
On 2026-07-25 15:38, Aaron Brown via tz wrote:
In addition to the significant errors that have already pointed out,
the sentence "For most of history, Earth's rotation has been
gradually slowing — tidal friction from the moon drags on Earth's
oceans, braking the planet's spin by roughly two milliseconds per
century." should really say "For most of history, Earth's rotation
has been gradually slowing — tidal friction from the moon drags on
Earth's oceans, braking the planet's spin by roughly two
milliseconds*/day* per century."
You are right that the length of the day, LOD, being a measure of the
rate difference LOD = 1 - d(UT1)/d(TT) between UT1 and TT (or, in
practice, TAI), should be specified in units ms/d (milliseconds
per day)
rather than in ms. In fact, [1, page 186] pretends that IERS
Bulletin B
gives LOD "ïn milliseconds per day" even though all the IERS
Bulletins B
use the unit ms (effectively indicating LOD·(1 d) rather than LOD).
And [1, page 646] defines LOD (incorrectly) as a time value rather
than
a rate.
Astronomers very rarely use quantity equations, they mostly use
numerical
equations with units that are often only implied or only sloppily
indicated.
[1] Sean E Urban, Kenneth P Seidelmann (eds): "Explanatory Supplement
to the Astronomical Almanac. 3rd edition". University Science
Books.
36 + 676 p. ISBN 978-1-891389-85-6. 2013 Mill Valley CA.
Michael Deckers.
C04 gives LOD as 100-nanoseconds (hectonanoseconds)
Combined solution C04 for Earth Rotation
Parameters consistent with International Terrestrial
Reference Frame 2014
https://hpiers.obspm.fr/eoppc/eop/eopc04_14/C04.guide.pdf
https://hpiers.obspm.fr/eoppc/eop/eopc04_20_v3/eopc04_IAU2000.62-now
You may find this interesting:
Contributions of core, mantle and climatological processes to Earth’s
polar motion
https://www.nature.com/articles/s41561-024-01478-2
