Earth's spin is slowing at a rate of 1.8 milliseconds per century

[Calista241]

Source: LA Times

The latest findings in Earth science are brought to you by ancient astronomers who observed the heavens as much as 2,700 years ago.

Thanks to hundreds of records of lunar and solar eclipses carved in clay tablets and written into dynastic histories, modern scientists have determined that the amount of time it takes for Earth to complete a single rotation on its axis has slowed by 1.8 milliseconds per century, according to a report published Wednesday in Proceedings of the Royal Society A.

It may not sound significant, but over the course of 2½ millenniums, that time discrepancy adds up to about 7 hours.

In other words, if humanity had been measuring time with an atomic clock that started running back in 700 BC, today that clock would read 7 p.m. when the sun is directly overhead rather than noon.



Read more: http://www.latimes.com/science/sciencenow/la-sci-sn-earth-longer-days-20161205-story.html

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Interesting.

[rug]

1. I thought I felt something.

[Travis_0004]

2. Earthquakes can have an impact on this

I know the earthquake in Japan was said to slow the earths rotation down 1.8 microseconds.

Given a large enough budget we could scrape earth off mountains and dump it into the ocean to speed the earth back up. Obviously this is a waste, but it would work if we threw enough resources at it.

[AtheistCrusader]

3. Someday the moon will tidelock the earth.

It is inevitable. Unless something destroys either body before that can occur.

[briv1016]

7. It already is.

Tidal breaking is what is slowing Earth. Interestingly the Moon is also moving away from Earth, so Earth will never be tidaly locked with the Moon. (At least not before the Sun swallows the Earth.)

ETA: I ment the Moon is Tidaly Locked, not the Earth.

[muriel_volestrangler]

9. It would be after the Sun becomes a red giant

http://www.universetoday.com/128350/will-earth-lock-moon/

so it'll be a minor part of Earth's history, since all life will have been wiped out.

[AtheistCrusader]

14. Not necessarily.

The earth's orbit will change, we'll be further out when the chromosphere is occupying the earth's current orbit.

[muriel_volestrangler]

15. I've not heard anyone say that life of Earth could survive the red giant phase

It's not a question of whether the outer edge of the Sun actually reaches us, just whether the radiation reaching the Earth is too much for life or liquid water.

[AtheistCrusader]

17. Ah, gotcha.

I do not know, but now I'm interested to research.

[Kotya]

23. The earth will be uninhabitable in 600-800 million years

Long before the sun turns into a red giant five billion years from now.

In 600 million years, disruptions to the carbonate–silicate cycle due to increased solar luminosity will cause plate tectonics to cease with carbon dioxide levels falling to the point at which C3 photosynthesis is no longer possible. All plants that utilize C3 photosynthesis (99 percent of present-day species) will die. 200 million years later, C4 photosynthesis is no longer possible. All multicellular life dies out.

And there's nothing we can do to stop this.

https://en.wikipedia.org/wiki/Timeline_of_the_far_future

[Dobro In Utero]

4. My days are already long enough, dammit.

[itsrobert]

5. All track records will now need asterisks

Last edited Wed Dec 7, 2016, 05:15 PM - Edit history (1)

Slowing Earth means less centrifugal force.

[Calista241]

6. On the bright side, I can now lose weight by doing nothing! N/t

[GummyBearz]

19. What?

Did the equation change since I took physics? Gravitational force is solely dependent on mass last I knew

[progree]

8. Whoever wrote this article probably voted for Trump - doesn't know shit about math

time it takes for Earth to complete a single rotation on its axis has slowed by 1.8 milliseconds per century, according to a report published Wednesday in Proceedings of the Royal Society A.

It may not sound significant, but over the course of 2½ millenniums, that time discrepancy adds up to about 7 hours.

Uhhhhhhhhhhhhh

1.8 milliseconds in a century is 18 milliseconds in a millenium, which is 45 milliseconds in 2 1/2 milleniums. The last time I checked, 45 milliseconds is a long long way from 7 hours.

[muriel_volestrangler]

10. that's 45 milliseconds extra in a year; add up all the years and you get the 7 hours

If you want to see the maths for the 7 hours, it's in the paper: http://rspa.royalsocietypublishing.org/content/472/2196/20160404

On edit: sorry, that 45ms figure is not 'in a year'; that's how much longer each day is now, compared to 2,500 years ago. A year is about 16 seconds longer.

[TwilightZone]

11. From the paper: "+1.8 ms per century"

It's not per year. I think the LA Times article is misinterpreting what the 7 hours is representing.

[muriel_volestrangler]

12. No, the LA Times has got it right; read the paper, about 'delta T'

which is what the observations give us as about 7 hours over 2,500 years. They then work out that is a 1.8 ms increase in the length of a day every century. The LA Times correctly says "In other words, if humanity had been measuring time with an atomic clock that started running back in 700 BC, today that clock would read 7 p.m. when the sun is directly overhead rather than noon. "

[TwilightZone]

13. Ok, that makes more sense.

The 45ms per year was throwing me off. It's more like (highly oversimplified) a couple cumulative seconds per day the first century, that couple plus a couple more the second, and so on, compounding the effect for 2500 years.

Got it, thanks. Hence, the need for occasional exceptions and adjustments.

Edit: meant century, typed year. Oh, the irony. lol

[progree]

24. Revision I.

It looks like I was right about the speed of the clock at the end of 25 centuries -- but I was leaving out the cumulative effect of the slowdown (sigh)

Let's say we have two clocks -- the atomic clock that is tuned to absolute time (decay rate of cesium or whatever) -- and a geoclock that is reset frequently so that earth's rotation always takes 24.00000000000000000000 hours -- i.e. as the earth slows down, the geoclock's speed and time is reset accordingly.

For the first century that geoclock runs from 0 to 1.8 ms slow -- that is during the first day it is 0 ms slow, and in the last day of the century the day is 1.8 ms longer than what the atomic clock says the length of the day is. On average during the century the geoclock is running 0.9 ms/day slow.

So for the first century, the geoclock will lose 0.9 ms * 36,525 days/century = 32,872 ms = 32.9 sec in time relative to the atomic clock.


For the second century that geoclock runs from 1.8 ms to 3.6 ms slow -- that is during the first day it is 1.8 ms slow, and in the last day of the century the day is 3.6 ms longer than what the atomic clock says the length of the day is. On average during the century the geoclock is running 2.7 ms/day slow.

So for the second century, the geoclock will lose 2.7 ms * 36,525 days/century = 98,618 ms = 98.6 sec in time relative to the atomic clock.

Cumulatively for the first 2 centuries, the geoclock has lost 32.9 sec + 98.6 sec = 131.5 sec

For the 3rd century, the geoclock is between 3.6 and 5.4 ms slow -- an average of 4.5 ms/day slow. So for the third century, the geoclock will lose 4.5 ms * 36,525 days/century = 164,362 ms = 164 sec in time relative to the atomic clock.

Cumulatively for the first 3 centuries, the geoclock has lost 32.9 sec + 98.6 sec + 164 sec = 295.5 sec

Carrying this out for 25 centuries:

[div style="display:inline; font-size:1.37em; font-family:monospace; white-space:pre;"] 1 2 3 4 24 25
[div style="display:inline; font-size:1.37em; font-family:monospace; white-space:pre;"](0.9 + 2.7 + 4.5 + 6.3 + ... + 42.3 + 44.1 ) * 36525 = 562.5 * 36525 = 20,545,312 ms = 20,545 sec

= 5.7 hours.

So cumulatively, from this math, the geoclock is behind the atomic clock by 5.7 hours.

My math above was crude, using intervals of a century. I'd get a larger number using smaller intervals like a year long, and an even larger number by using yet smaller intervals like a day long and so on. (Yes, I know, an integral calculus problem as delta T -> 0).

So yeah, I can believe the 7 hours.

Is there somewhere they explain that in the paper? I didn't see anything like this.

[muriel_volestrangler]

25. In the paper, they work out the delta T over centuries from observations

(mainly eclipses) and then fit a parabolic curve to that (and then look at deviations from that). See figure 9, and their equation 4.1. (They've already said, in section 1(b), that theory gives a constant rate of change in day length, so that the accumulated delta T should be parabolic). Then, in section 5.1, they differentiate that to get the long term figure of 1.78 milliseconds per century.

In fact, the 7 hours is the figure for the currently calculated 2.3 ms per century - calculated from satellite measurements of earth-moon tidal friction. Their analysis of the eclipse etc. records gives delta T of about 22000 seconds (figure 9), which is more like 6 hours. So the 'news' from this paper, which is in the abstract, is " the change in the length of the mean solar day (lod) increases at an average rate of +1.8?ms per century. This is significantly less than the rate predicted on the basis of tidal friction, which is +2.3?ms per century."

[bluedigger]

18. Well, there's some news I don't need to fret over.

[keithbvadu2]

20. We hear that the sun will go super nova in 4 or 5 billion years and burn the earth to a crisp.

We hear that the sun will go super nova in 4 or 5 billion years and burn the earth to a crisp.

I'm a patient kinda guy.

I can wait.

[VWolf]

22. Red giant, not supernova, but the end result is essentially the same for puny Earth n/t

[yurbud]

21. I thought it felt a little off.

[underpants]

27. LOL

[milestogo]

26. Its because of all the junk food.

We're getting fat, and it slows everything down.

Global slowing, they call it.

[montana_hazeleyes]

29. There you go! lol

[underpants]

28. Stop the world, I want to get off

and I thought my watch was just off

[pressbox69]

30. I think it's because the Chinese are ticked off about that Trump call.

All hopping mad up and down at the same time to effect the earth's rotation.

[yellowcanine]

31. If it stops I am definitely getting off.