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Earth Science Technology

Earth's Day Lengthens By Two Milliseconds a Century, Astronomers Find (theguardian.com) 140

Posted by BeauHD from the tick-tock dept.
Researchers at Durham University and the UK's Nautical Almanac Office compiled nearly 3,000 years of celestial records and found that with every passing century, the day on Earth lengthens by two milliseconds as the planet's rotation gradually winds down. The Guardian reports: The split second gained since the first world war may not seem much, but the time it takes for a sunbeam to travel 600km towards Earth can cost an Olympic gold medal, as the American Tim McKee found out when he lost to Sweden's Gunnar Larsson in 1972. For those holding out for a whole extra hour a day, be prepared for a long wait. Barring any change in the rate of slowing down, an Earth day will not last 25 hours for about two million centuries more. Researchers at Durham University and the UK's Nautical Almanac Office gathered historical accounts of eclipses and other celestial events from 720BC to 2015. The oldest records came from Babylonian clay tablets written in cuneiform, with more added from ancient Greek texts, such as Ptolemy's 2nd century Almagest, and scripts from China, medieval Europe and the Arab dominions. The ancient records captured the times and places that people witnessed various stages of solar and lunar eclipses, while documents from 1600AD onwards described lunar occultations, when the moon passed in front of particular stars and blocked them from view. To find out how the Earth's rotation has varied over the 2,735-year-long period, the researchers compared the historical records with a computer model that calculated where and when people would have seen past events if Earth's spin had remained constant. The astronomers found that Earth's spin would have slowed down even more had it not been for a counteracting process. Since the end of the most recent ice age, land masses that were once buried under slabs of frozen water have been unloaded and sprung back into place. The shift caused the Earth to be less oblate -- or squished -- on its axis. And just as a spinning ice skater speeds up when she pulls in her arms, so the Earth spins faster when its poles are less compressed. Changes in the world's sea levels and electromagnetic forces between Earth's core and its rocky mantle had effects on Earth's spin too, according to the scientists' report in Proceedings of the Royal Society.
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Earth's Day Lengthens By Two Milliseconds a Century, Astronomers Find More

Earth's Day Lengthens By Two Milliseconds a Century, Astronomers Find

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  • I suggest we tie a string around the equator, then launch a mighty rocket into space that we've tied to the end.

    I foresee no problems with this plan.

    • Everybody run towards the east, as fast as you can!

    • Re: (Score:3)

      by tomhath ( 637240 )
      Didn't Superman spin the Earth backwards by flying around it opposite to the rotation? That seems like it would work to speed it up if he flew the other way. Just need to contact Clark.

      • Re:Clearly Global Slowing is a problem that must b (Score:4, Funny)

        by Colin Castro ( 2881349 ) on Thursday December 08, 2016 @12:04PM (#53446479)
        Why would you contact Clark? He's just a reporter.

      • Didn't Superman spin the Earth backwards by flying around it opposite to the rotation? That seems like it would work to speed it up if he flew the other way. Just need to contact Clark.

        I always thought that too, but apparently from reading articles about the movie more recently, they were trying to show him flying so fast that he went back in time (supposedly just going around the Earth so he didn't get lost).

        • Didn't Superman spin the Earth backwards by flying around it opposite to the rotation? That seems like it would work to speed it up if he flew the other way. Just need to contact Clark.

          I always thought that too, but apparently from reading articles about the movie more recently, they were trying to show him flying so fast that he went back in time (supposedly just going around the Earth so he didn't get lost).

          So how did they explain away the Earth actually stopping, then reversing its rotation, which would have been more disastrous than the nuke detonating on the San Andreas Fault?

          • Didn't Superman spin the Earth backwards by flying around it opposite to the rotation? That seems like it would work to speed it up if he flew the other way. Just need to contact Clark.

            I always thought that too, but apparently from reading articles about the movie more recently, they were trying to show him flying so fast that he went back in time (supposedly just going around the Earth so he didn't get lost).

            That's how Superman travelling backwards in time would see the Earth. As time stopped for him, so would the spinning of the Earth. As he moved backwards in time, the Earth would appear to move in reverse and all the actions would be shown like a movie being played backwards as they appeared in the film.

            So how did they explain away the Earth actually stopping, then reversing its rotation, which would have been more disastrous than the nuke detonating on the San Andreas Fault?

  • New low? (Score:1)

    by Anonymous Coward

    The split second gained since the first world war may not seem much, but the time it takes for a sunbeam to travel 600km towards Earth can cost an Olympic gold medal, as the American Tim McKee found out when he lost to Sweden's Gunnar Larsson in 1972.

    Is this a new record low for poor writing on slashdot? Gold medal for most tortured use of an tenuous comparison in a pointless comparison? Our judges are very excited...

    • Re: (Score:3)

      by Potor ( 658520 )

      That was clearly the last time a split-second mattered in the Olympics.

      But anyway, that poor writing is the fault of the Guardian, not /.

    • If they had to go all the way back to 1972 to find an example then they just proved their own example is crap.

      PS: Try Formula1 next time.

  • so it's all been a lie? (Score:1)

    by Anonymous Coward

    my life? my pay? my vacation? all a lie?

  • Tidal Forces (Score:5, Informative)

    by saibot834 ( 1061528 ) on Thursday December 08, 2016 @03:37AM (#53444919)

    Interestingly, this also has an effect on the moon. The reason why the earth's rotation is slowing are the tidal forces. Part of the energy lost from the Earth's momentum goes into the Moon's own orbit. As a result, the moon is actually getting further and further away from us, at a rate of 38 mm (1.5 in) per year. Somewhat counter-intuitively, the Moon actually gets slower that way, despite the energy put in is in the prograde direction, i.e. increases its velocity. The reason is the higher orbit. Sources:
    Tidal effects on the Moon [wikipedia.org]
    Earth's rotation [wikipedia.org]

  • China's Monster Three Gorges Dam (Score:4, Interesting)

    by invictusvoyd ( 3546069 ) on Thursday December 08, 2016 @03:57AM (#53444945)
    Raising 39 trillion kilograms of water 175 meters above sea level will increase the Earthâ(TM)s moment of inertia and thus slow its rotation. However, the effect would extremely small. NASA scientists calculated that shift of such as mass would increase the length of day by only 0.06 microseconds and make the Earth only very slightly more round in the middle and flat on the top. It would shift the pole position by about two centimeters (0.8 inch). Note that a shift in any objectâ(TM)s mass on the Earth relative to its axis of rotation will change its moment of inertia, although most shifts are too small to be measured (but they can be calculated). http://www.businessinsider.com... [businessinsider.com]

  • Howlin' Wolf asked How Many More Years? [youtube.com]

    Now I'm gonna ask how many more milliseconds!

  • I'm not sure I really understand the use of the Babylonian clay tablets for this - at best they'll tell you what day it happened, but we're talking about ~6000 years ago, so 60 centuries times 2 milliseconds, that's ... Did the Babylonians really calculate time in 1/100s of a second?

    • Re: (Score:3, Informative)

      by skullandbones99 ( 3478115 )

      Using computer modelling I suspect the location of the shadow of the eclipse is dependent on the spin rate of the Earth. Therefore, by knowing where people saw the eclipse and how much of the sun could be seen will be sufficient to calculate the rotational position of the Earth at the time of the eclipse. Then compare that position with the computer model. So knowing the exact time of the observations of the eclipse to the order of milliseconds is unnecessary.

  • Science coverage with AD (Score:1, Insightful)

    by Anonymous Coward

    I'd really like to see the end of using the AD and BC. We have BCE and CE that do not require invoking a mythological being.

    • And what is the dividing point between BCE and CE?

      Not to mention it's strange to call it the "Common Era", when most of the world didn't know about the rest of the world at the start of the era.

      • And what is the dividing point between BCE and CE?

        Not to mention it's strange to call it the "Common Era", when most of the world didn't know about the rest of the world at the start of the era.

        "Common Era"? Hrrm. I always through CE stood for "Christian Empire".

    • I'd really like to see the end of using the AD and BC. We have BCE and CE that do not require invoking a mythological being.

      It's called knowing your audience.

      Yes, science referred to ancient Greek texts, but using BCE and CE would be akin to them speaking Greek to the masses to deliver this message.

    • We could just use a negative sign. But you'd have to be careful with calculations because some stupid sod forgot year 0.

    • Re:Science coverage with AD (Score:5, Insightful)

      by hackertourist ( 2202674 ) on Thursday December 08, 2016 @08:49AM (#53445485)

      Mythology or not, our calendar has a start date based on an event in Christian history. Trying to hide that fact by using a different abbreviation reeks of revisionism.

      • Mythology or not, our calendar has a start date based on an event in Christian history. Trying to hide that fact by using a different abbreviation reeks of revisionism.

        No, it's an event in Christian mythology. Nothing has happened to elevate it to the level of history.

        • ... revisionism at its best. was christ born in that vicinity of years? yes, the man later to be known as christ was born in a 30 year window of that time. was he a jew yes. was he the son of god? debatable. saying christ's existence in relation to the year 0 is mythological, is not historically accurate.

          there was a dude, later people worshipped him as the son of god. we use his putative birthday as the 0 point of our calendar.
          that's all acceptable to me, as one so made that I cannot believe, yet living

          • ... revisionism at its best. was christ born in that vicinity of years? yes, the man later to be known as christ was born in a 30 year window of that time.

            [citation needed]

            There is not one single historical point of evidence for the man's existence. Every supposed eyewitness account is from the same collection of related works allegedly created by three authors. I love the idea of Jesus Christ as much as the next guy, but there is literally no historical evidence for his existence. The closest thing you get is one historian repeating hearsay.

            This doesn't mean there was no Christ. The absence of evidence is not the same as incontrovertible evidence of absence

            • i'm not an expert, neither are you, but

              https://en.wikipedia.org/wiki/... [wikipedia.org]
              http://www.abc.net.au/religion... [abc.net.au]

              for those that are, apparently, the probability is that it is more likely that there was a historical jesus than not.

              perused a bit, seems like you could liken the "christ myth theory" as a splinter theory that the majority of scholars of the subject dismiss. and that the two points widely accepted as being historic in jesus' life are the crucifixion, and baptism by john the baptist. everything else is a

              • apparently, study of ancient history falls apart if we require the kind of proof that you're looking for for a historical jesus.

                That's fine. We should require that kind of proof. Otherwise, it should be acknowledged to be the study of mythology, and the places in which it intersects with observable reality.

                • yes, let's just take the tactic of the young earth creationists and the intelligent design proponents for our own.

                  you throw out the tenets of an entire field of scientific study, because they're not in keeping with your world view, you are doing the same thing as those you look down on.

                  how much first hand evidence would you expect for a jewish carpenter living on the fringes of the roman empire? one cult among many cults, that only rose to prominence because it got lucky?

                  it's a damn miracle that it got the

          • there was a dude, later people worshipped him as the son of god. we use his putative birthday as the 0 point of our calendar.

            Your calendar changes year on 25th December? Which country do you live in?

            • damn right, in god's country, in the good ole United States of 'murica.

              a 30 year period where people think his birthday was. which isn't tied to the 25th at all. and 0 point of the years. as you should have interpreted i meant.

              https://en.wikipedia.org/wiki/... [wikipedia.org]

              you may use whatever year numbering system you want, and many cultures do maintain their own internal year counting system. but you MUST know the western one. Good or bad, the role and impact that christendom has had on global affairs, requires tha

              • How come, if 'Murika is a Christian country as they claim, they're worshipping that (probably non-existent) Jew, Jesus son of Joseph?

                • cuz real 'muricans don't need no stinkin' facts.

                  also, nothing wrong with jews that europe wasn't entirely responsible for.

                  more jews in 'murica than in israel.

                  "German Interviewer: Mr. Williams, why do you think there's not so much comedy in Germany?
                  Williams: Did you ever think you killed all the funny people?"

                  I'm american, the christian culture and roots have colored me to my outlook, to my language, it's inextricably permeated the fabric of my character. it has in part contributed and built a society tha

                  • it has in part contributed and built a society that is better than all that have come before it,

                    How do your Native American, First Nations, and/ or Hawaiian friends react when you describe their cultures in these terms to their faces?

                    i value too much the gaurantees on my freedoms that my birthright gives me. any other country on earth. christian values have helped build these things,

                    Actually, your own Supreme court has repeatedly traced much of this back to Britain, via the "Glorious Revolution" of the 1670

                    • "How do your Native American, First Nations, and/ or Hawaiian friends react when you describe their cultures in these terms to their faces?"

                      oh what noble savagery. don't romanticize or idealize those nations and those times. hawaii was unified by war under kamehameha, war war war, that is the natural state of humanity it seems. north america was no different.

                      I include western europe when I speak of christendom.

                      the freedom I value most is actually that of speech. and britain's got some hatespeech laws on

                    • i'd rather they legislate actions, not words, and not thoughts.

                      Until someone actually develops an evidence-quality "mind-reading machine" (polygraphs are laughed at by the courts here - I can't remember when I last heard of someone submitting polygraph evidence in a UK court ; the reports a year or two ago of some Indian (IIRC) company trying to develop an MRI-based way of detecting someone's state of mind doesn't seem to have appeared in court yet), actions are the only things that can be prosecuted. Which

    • That would also mean having to change the names of several days of the week, as they are taken from (I believe), a mix of Roman mythology and Norse mythology.

  • So they should be (Score:3)

    by wonkey_monkey ( 2592601 ) on Thursday December 08, 2016 @04:43AM (#53445001) Homepage

    Earth's Day Lengthens By Two Milliseconds a Century, Astronomers Find

    How could they let this happen? Damn right they should be fined!

    • Re: (Score:2)

      by sconeu ( 64226 )

      <sarcasm> Thanks, Obama!!! </sarcasm%gt;

      Per the Americans with Disabilities Act, sarcasm tags have been added to assist the sarcasm-impaired

  • 2 milli-seconds per century? (Score:5, Interesting)

    by tal_mud ( 303383 ) on Thursday December 08, 2016 @05:44AM (#53445103)

    I must be missing something. The oldest records they observed were from 3000 years ago, i.e. 30 centuries, or 60 milli-seconds. How in heavens sake do they decide that the recorded eclipse was off by that little? Their article mentions "thousands of observations". Even assuming 10,000 observations, the time accuracy for statistically meaningful results would seem to be sqrt(10,000)*60ms or 6sec. No way the ancient observations were so accurate.

    • Re: (Score:3, Insightful)

      by Anonymous Coward

      I must be missing something. The oldest records they observed were from 3000 years ago, i.e. 30 centuries, or 60 milli-seconds..

      No, it's 2ms / day / century, so 30 * 2 ms * 365.25 * 3000 / 2, or about 9 hours. I think ancient observations were that accurate.

      • Comment removed based on user account deletion

        • Re: (Score:1)

          by Anonymous Coward

          It may mean that the rate of lengthening (in mm/century) is increasing by 2mm a day.

        • I understand 2 ms per day, but what does the century mean?

          A century means (approximately) 36,525 days.

          Actually, once you get to that sort of duration, it's damned difficult to define durations in astronomical terms because both the rotation axis of the Earth, and the plane of orbit of the Earth around the Sun change noticeably over such time periods. And since you're also getting to the level where you need to take into account the gravitational influences of Venus, Mars and Jupiter on the Earth's motions

      • Re: (Score:1)

        by Anonymous Coward

        This is correct. GP is not accounting for the cumulative difference. Additionally, the measurements are less concerned with time and more concerned with location, i.e. who saw the eclipse vs. when. by modelling the moon's orbit they can figure out the time precisely, the research is trying to determine what part of the earth was underneath it, thus the rotational speed of the earth.

  • I really wish the kerfuffle around "fake news" would shine a light on the fact that a lot of science "reporting" on the intertubes is mischaracterized or just plain wrong. This article is a perfect example. Every article I've seen on sites that are not hard science reports it as if the fact that the earth is slowing is a new discovery. It's not, we've known for decades (at least) that this was the case. The linked Guardian article doesn't even mention that until ten sentences into a fourteen sentence pi

    • This article is a perfect example. Every article I've seen on sites that are not hard science reports it as if the fact that the earth is slowing is a new discovery. It's not, we've known for decades (at least) that this was the case.

      Centuries. The first mention of this that I've seen was by Great Britain's Astronomer Royal in about 1735. George Darwin (son of Charles) did detailed mathematical analysis of the problem in them late 1870 to 1880s.

  • Tim McKee got silver in the 1972 Olympics (didn't qualify for a tie-breaker) because he was slower than his competitor... by less than a hundredth of a second.

    But this really couldn't have much less to do with the story. It's a random fact, not on topic. TFA: WTF?

  • I'm missing something. Leap seconds .. (Score:1)

    by Anonymous Coward

    The article says 2 milliseconds per century, but we've already added 27 leap seconds since 1972 ..

    So, what am I missing..?

    • Re: (Score:3, Informative)

      by burhop ( 2883223 )

      The article says 2 milliseconds per century, but we've already added 27 leap seconds since 1972 ..

      So, what am I missing..?

      Leap seconds (and leap years) are due to the number of rotations of the earth in a year not being exactly 365. If you think about it, why would they be. There is no reason the earth should rotate exactly 365 time in one trip around the sun. So, to keep December from gradually creeping into the summer, we have to fiddle a bit with the calendar.

      In this case, we are just talking about the rotation speed of the earth. In a closed system, the rotation speed can be changed by moving the mass around the Earth,

    • Re: (Score:3)

      by suutar ( 1860506 )

      I believe the article is missing a clear indication that "2ms/century" is the rate at which the length of a _day_ is increasing. So it really means "the lengthening of a day is accelerating by 2ms/day/century". And like in distance, the acceleration doesn't tell you how much something changed by itself, you have to know what the starting rate of change was.

    • The article says 2 milliseconds per century, [...]So, what am I missing..?

      2 milliseconds per day per century,

      A change of 2ms per day would add up to a difference of 1s in about 500 days.

      I make the Julian Day for 1972-01-01 (ISO8601) to be 2441318 and for 2017-01-01 to be 2457755 (because I've done the legwork previously for calculating Julian Days) for a difference of 16437 days. At about 1 second per 500 days, then there should have been about 32 or 33 leap seconds since 1972-01-01.

      we've already added 2

  • "The split second gained since the first world war may not seem much, but the time it takes for a sunbeam to travel 600km towards Earth can cost an Olympic gold medal, "

    What he/she said was, "Being second by a small amount of time will cause you to not be first"

    I'm pretty sure being second by any amount of time, large or small, will cause you to not be first too.

  • I don't understand this:
    "And just as a spinning ice skater speeds up when she pulls in her arms, so the Earth spins faster when its poles are less compressed"

    Less compressed is spreading out, so the spin would be slower, not faster.

    • "poles less compressed" means the poles are farther apart, effectively elongating the planet along its spinning axis. This will "shrink" the equator; statement is correct.

    • poles, the arctic and antarctic ice receded, and the earth got less pumpkin shaped and more billiard shaped. the ice at the poles was compressing the earth's volume to the equator, once the ice melted, the poles sprung back and the equator circumference got slightly smaller.

      • Actually, the largest component of the change is from the Greenland icecap. Since it is not even vaguely symmetrical around the north pole (the north pole is not within the area of the Greenland icecap) , AND it is considerably above sea level (average surface elevation 2100m), then the melting of ice from the icecap and moving it down to the sea adds up to most of the effect. (Antarctica is higher than Greenland, but much more symmetrically placed.)
  • 2 million centuries? Dang, that's like 2,000 kiloyears.
  • 1/7 / 0.002 = 71.4

    So 7,100 years from now we're gonna need one leap second per week, or 50 leap seconds at once at the end of each year, whichever is easier to organise. That's gonna be tough.

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