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.
