# Earth lost 3 hours over 2000 years? **URL:** \ **Category:** Factual Questions\ **Created:** [April 27, 2022, 8:52am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527 "2022-04-27T08:52:28Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 27, 2022, 8:52am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/1 "2022-04-27T08:52:28Z")
An article ([free link](https://www.nytimes.com/2022/04/25/science/time-second-measurement.html?unlocked_article_code=AAAAAAAAAAAAAAAACEIPuomT1JKd6J17Vw1cRCfTTMQmqxCdw_PIxftm3iWka3DJDmwfiP8eAoWG8EqKeatmap4o0j-cQtMENbImX-Fow-pSOVArSxWtptHMvqU5FBgPiND5WHIqjdWKVKok8DTuYy7gcLwln-zntFePbmO5RKDfhXI-dAszoo8ycwv52HQIzqiWQuFly5Ipi6dac5N5RDoAYSOMuPL6WV4paJjdMEaqukRhUPpZWDrTgdea97kFFQxYAl_MR3t8in0uvJIeYJhEefaicGNzPZb2kr4TCWd3LYu2BJNXRonckrRisbalugW7afSdF5AcixZQngUsGYPF&smid=url-share)) in the NY Times says: > [@](#): > > But the definition had problems. Earth is gradually slowing in its daily rotation; days are growing slightly longer and so the astronomical second is, too. Those small differences add up. Based on extrapolations from historical eclipses and other observations, **Earth as a clock has lost more than three hours over the past 2,000 years.** [emphasis mine] Anyone know what they’re talking about? The Earth is slowing down, but no where near that fast. Yes, it’s a newspaper, which means they always get something wrong when talking about science. But they must have gotten this from somewhere, even if they misunderstood. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [April 27, 2022, 9:39am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/2 "2022-04-27T09:39:27Z")
That is a measure of the accuracy of Earth’s rotation, not it’s duration. In two thousand years, the Earth (as a clock) has ‘ticked off’ about 17 million hours; in that time it has ‘lost’ three hours. That is an accuracy of one part in six million, give or take a bit. Not too bad. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [April 27, 2022, 9:40am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/3 "2022-04-27T09:40:55Z")
The Earth’s rotation is irregular. Sometimes it is necessary to add a [leap-second](https://en.wikipedia.org/wiki/Leap_second) to the clock. _A **leap second** is a one-[second](https://en.wikipedia.org/wiki/Second) adjustment that is occasionally applied to [Coordinated Universal Time](https://en.wikipedia.org/wiki/Coordinated_Universal_Time) (UTC), to accommodate the difference between precise time ([International Atomic Time](https://en.wikipedia.org/wiki/International_Atomic_Time) (TAI), as measured by [atomic clocks](https://en.wikipedia.org/wiki/Atomic_clock)) and imprecise [observed solar time](https://en.wikipedia.org/wiki/Solar_time#Mean_solar_time) ([UT1](https://en.wikipedia.org/wiki/UT1)), which varies due to [irregularities](https://en.wikipedia.org/wiki/Earth_rotation#Changes) and long-term [slowdown in the Earth’s rotation](https://en.wikipedia.org/wiki/%CE%94T_(timekeeping)). The UTC time standard, widely used for international timekeeping and as the reference for [civil time](https://en.wikipedia.org/wiki/Civil_time) in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment._ A difference of about a thousand seconds over two thousand years doesn’t seem unreasonable. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [April 27, 2022, 11:33am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/4 "2022-04-27T11:33:23Z")
> [@Peter\_Morris](#): > > A difference of about a thousand seconds over two thousand years doesn’t seem unreasonable. Nitpick: three hours is closer to 10,000 seconds than to 1,000. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [April 27, 2022, 11:53am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/5 "2022-04-27T11:53:18Z")
> [@dtilque](#): > > Anyone know what they’re talking about? Here you go: > **[NASA - Polynomial Expressions for Delta T](https://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html)** > > This is NASA's official moon phases page. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [April 27, 2022, 11:55am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/6 "2022-04-27T11:55:39Z")
Here’s a [page from NASA](https://eclipse.gsfc.nasa.gov/SEhelp/deltat2004.html) where I suspect the numbers were drawn from. The numbers there compare Universal Time (defined by Earth’s rotation) to Terrestrial Time (a theoretical uniform clock). In particular, due to the gradual slowing of the Earth’s rotation, it is estimated that since the year 0\*, the rotations of the Earth have taken about 10580±260 seconds longer than one would have expected from a uniformly rotating Earth. That works out to just shy of three hours. \*Note to pedants: go away ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [April 27, 2022, 12:24pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/7 "2022-04-27T12:24:17Z")
Right. The basic answer is “they mean three hours total accumulated time, while you were thinking three hours PER DAY, which is way too much over just a few thousand years.” (but does accurately describe the slow-down over the last billion years, I believe). ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [April 27, 2022, 6:10pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/8 "2022-04-27T18:10:02Z")
A fairly [common](http://www.talkorigins.org/indexcc/CE/CE011.html) young-earth creationist argument involves greatly overestimating the slowdown in earth’s rotation, basically by making the mistake of thinking that every time a leap second is added by timekeepers, it is because earth’s rotation has slowed by a second since the last leap second, rather than just the clock being consistently off by a second per couple of years. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [April 27, 2022, 10:56pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/9 "2022-04-27T22:56:32Z")
Well, it’s had 4.5 billion years to slow down since the Earth was formed out of rotating interstellar dust elements clumping together. It was rotating then, but has been slowing ever since, and is still slowing now, I think. Presumably, it will stop rotating entirely some day, and be locked like the moon or Mercury. Probably some astronomer has calculated that time. Though we may be changing it by our rocket launches – these are all aimed in one direction, to take advantage of the boost given by the earth’s rotation. But each such ‘boost’ results in some tiny slowing of the earth’s rotation. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [April 27, 2022, 11:19pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/10 "2022-04-27T23:19:33Z")
> [@Tim\_T-Bonham.net](#): > > Presumably, it will stop rotating entirely some day, and be locked like the moon or Mercury. Probably some astronomer has calculated that time. Well, the day might be as long as one month, but then you could imagine solar tides slowing it down further. But this sort of thing should take tens of billions of years; if you are just worried about the day being 25 or 26 hours long (not too bad, even) then you are OK for hundreds of millions of years yet. (Not 2000 years, obviously) ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [April 27, 2022, 11:26pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/11 "2022-04-27T23:26:09Z")
> [@Tim\_T-Bonham.net](#): > > Well, it’s had 4.5 billion years to slow down since the Earth was formed out of rotating interstellar dust elements clumping together. It was rotating then, but has been slowing ever since, and is still slowing now, I think. Presumably, it will stop rotating entirely some day, and be locked like the moon or Mercury. Probably some astronomer has calculated that time. The Earth will tidally lock to the Moon, not the Sun, but it’d take longer than the lifespan of the Sun anyway, so the Earth might not exist anymore. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [April 28, 2022, 12:05am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/12 "2022-04-28T00:05:24Z")
> [@RickJay](#): > > The Earth will tidally lock to the Moon, not the Sun, but it’d take longer than the lifespan of the Sun anyway, so the Earth might not exist anymore. The mathematical estimate for tidal sync between Earth and its moon seems to be 50 billion years. At this point, the moon would have gradually receded to an orbital period of the equivalent of about 47 contemporary days while the spin of Earth would gradually slow to that same period. But that is just raw numbers, which ignore the Sun going off main sequence in some 5~6 billion years, raising the density of the local medium by a factor of about 2 (increasing drag on the moon, moving it outward faster), or the solidifying of Earth’s core (loss of magnetosphere, causing air and seas to go away in the solar wind, reducing lunar tidal drag) or, who knows what else. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [April 28, 2022, 12:22am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/13 "2022-04-28T00:22:24Z")
> [@Tim\_T-Bonham.net](#): > > Presumably, it will stop rotating entirely some day, and be locked like the moon or Mercury Mercury is not “locked” to the Sun. We used to think it was, but actually there are 3 Mercurial “days” in 2 Mercurial “years”. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 28, 2022, 8:37pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/14 "2022-04-28T20:37:45Z")
It’s sort of a lock, though. It’s what gets called a “resonant lock”. Even weirder, Venus actually has a resonance with Earth: Whenever we’re at the closest points of our orbits, she always shows the same face to us. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [April 28, 2022, 9:26pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/15 "2022-04-28T21:26:33Z")
> [@Chronos](#): > > she always shows the same face to us What _is_ she hiding? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [April 28, 2022, 10:36pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/16 "2022-04-28T22:36:25Z")
Don’t forget earthquakes. The big earthquake in Japan in 2011 sped up the rotation of the earth (thus shortening our days) by 1.8 microseconds. Other earthquakes have done something similar. > **[NASA - Japan Quake May Have Shortened Earth Days, Moved Axis](https://www.nasa.gov/topics/earth/features/japanquake/earth20110314.html)** > > The March 11, magnitude 9.0 earthquake in Japan may have shortened the length of each Earth day and shifted its axis. ---
**Author:** ![74westy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/74westy/32/3950_2.png) [@74westy](https://boards.straightdope.com/u/74westy)\ **Post date:** [April 28, 2022, 10:49pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/17 "2022-04-28T22:49:33Z")
Dams slow the rotation of the Earth by holding water at a high elevation than it would otherwise be at and increasing the Earth’s moment of inertia. Don’t know if that amounts to as much as 1.8 microseconds/day. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [April 28, 2022, 11:54pm UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/18 "2022-04-28T23:54:40Z")
She has a dark side. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [April 29, 2022, 12:55am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/19 "2022-04-29T00:55:30Z")
When Venus is closest to Earth, wouldn’t it be the dark side facing us? Why do planets, ships, and some other vehicles get feminine pronouns? ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [April 29, 2022, 1:12am UTC](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527/20 "2022-04-29T01:12:29Z")
> [@Senegoid](#): > > Why do planets, ships, and some other vehicles get feminine pronouns? Venus is named for a goddess, but it doesn’t usually get a feminine pronoun.\* Nor do planets named for gods usually get masculine pronouns. \*just like right there, usually the neuter pronoun [Next page](https://boards.straightdope.com/t/earth-lost-3-hours-over-2000-years/963527.md?page=2)