As can be seen in this diagram, the length of the solar day has varied


considerably the last century. But the diagram is incomplete and doesn't show the very last years. Can anyone tell me how this graph would proceed and where it would be today, if extended using data from recent years?

Diagram of the length of solar day


It appears the rotation speed of Earth and thereby length of the solar day varies more from month to month than it does from year to year. What I am looking for is the average solar day length over a period of a year, and by how much it differs from 24*60*60 seconds.

I would also appreciate links to raw data that I can use to create my own graph.

  • $\begingroup$ You should be aware that month to month, the variation is on the order of 10 seconds. $\endgroup$
    – Zach466920
    Mar 6, 2016 at 21:13
  • $\begingroup$ So you are saying that if the length of 30 consecutive solar days is n seconds, then the 30 following days may equal n +- 10 seconds? $\endgroup$
    – Alpha_Pi
    Mar 6, 2016 at 22:28
  • 1
    $\begingroup$ Actually, it's periodic, see Wikipedia. $\endgroup$
    – Zach466920
    Mar 6, 2016 at 22:31
  • $\begingroup$ Also see physics.stackexchange.com/q/469869/123208 $\endgroup$
    – PM 2Ring
    Aug 12, 2019 at 17:30

1 Answer 1


A more recent diagram of day length deviations:

enter image description here

(Image taken from https://en.wikipedia.org/wiki/File:Deviation_of_day_length_from_SI_day.svg)

The diagram was derived from this regularly updated raw data: http://hpiers.obspm.fr/eoppc/eop/eopc04/eopc04.62-now


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