Given that the earth's rotation has been slowing down by very slight amounts over time, forcing us to introduce leap seconds and so forth into our clocks and calendars, I would like to ask if this could be fixed by "generating" more spin via some sort of power plant like structure(s) with a massive spinning object. (would it be ideal for these to be on the equator?)

How much energy would be needed in order to change the length of a year by 1 second?

what about in order to eliminate February 29th such that we don't need a "leap day" anymore? (24 hours over 4 years) - note that for this, the spin would need to be altered such that the day is removed, but then returned to near its original state such that we don't keep losing days

related Q/A: the earth IS slowing down (rotationally)

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    $\begingroup$ You're going about this the wrong way. I need some more sleep. $\endgroup$ Commented Oct 26, 2014 at 17:07
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    $\begingroup$ We can organize a huge marathon before leaping day, all people running in the same direction of earth's rotation. That will slow down the Earth a little bit until people stop running. But I am not sure how many people you need. But for sure, the Chinese and the Indian will contribute disproportionately, and they have a different calendar, so they might not want to do it. $\endgroup$
    – user65081
    Commented Oct 26, 2014 at 17:29
  • $\begingroup$ @dmckee - You'll get one extra hour of sleep a week from now when daylight savings time ends. $\endgroup$ Commented Oct 26, 2014 at 20:44
  • $\begingroup$ Relevant XKCD: what-if.xkcd.com/26 $\endgroup$
    – Michal
    Commented Oct 26, 2014 at 22:37
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    $\begingroup$ @user2813274 No that only gets me 2 hours of accumulated time. I want two more hours in every single day. I believe I have to wait roughly 75 million years for that... (Figure assumes that Vernor Vinge used reasonable values in Across Realtime, because I'm not going to check it.) $\endgroup$ Commented Oct 27, 2014 at 1:23

1 Answer 1


A day is currently about 86400.002 seconds long. If we could just increase the Earth's rotation rate by a mere 2 milliseconds per day we would get rid of the need for those pesky leap seconds. No problem! We only need something that rotates with an angular momentum of 1.4×1026 joule-seconds about an axis pointing due south.

One way to do this would be to build a train track around the Earth at the equator. I'll assume a 20 meter long train car with a gross mass of 150,000 kg moving at bullet train speeds, 320 km/hour. There's room for about two million cars on this track. That gets us to 1.7×1020 joule-seconds. We would only need 800,000 such circum-equatorial trains. Alternatively, we would only need one such train if we could make the train move at 0.23 c.

Another approach would be to place a large rotating disc at the South Pole. For example, a uranium disc with a radius of 20 kilometers and a height of 28 meters rotating at 10,000 RPM will just about do it.

In other words, it can't be done.

  • $\begingroup$ Correct me if im wrong, but the train would only work as long as the train keeps moving, meaning it's not a permanent solution. Would the rotating disk be any different if you were to bring it up to speed and then rotate the entire spinning object such that it's not longer pointing due south? $\endgroup$ Commented Oct 27, 2014 at 1:08
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    $\begingroup$ Of course the trains have to keep moving. How to supply the fuel needed to keep those 800,000 globe-encircling bullet trains on the move is an exercise left to the reader. $\endgroup$ Commented Oct 27, 2014 at 1:13
  • $\begingroup$ @user2813274 Conservation of angular momentum is a fundamental principle. If you want a permanent change we'll build 800 mass drivers with relativistic muzzle velocities around the equator and shoot 1000 of the trains eastward from each one, one car at a time. Coping with the environmental effects of is another exercise for the reader. $\endgroup$ Commented Oct 27, 2014 at 1:15
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    $\begingroup$ @dmckee - I didn't present that solution for two reasons. One reason is that the OP wanted a solution involving rotation. Another is that shooting the train cars to the east won't work. You need to shoot them to the west to get rid of those leap seconds. Then again, you want a longer day, so shooting to the east works for you. $\endgroup$ Commented Oct 27, 2014 at 1:27

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