It has(n’t) been a long day
Stories from Physics
for 11-14
14-16
Fossil evidence from corals suggests that the length of the year 370 million years ago was between 385 and 410 days. A number of factors are causing the change in rotational speed of the Earth including: an acceleration in the rotation of the Moon, frictional forces due to the motion of the tides, and change to the Earth’s shape caused by the melting of glaciers making the Earth less oblate. As the mean solar day, defined as 86,400 seconds, does not precisely match the period of the Earth’s rotation, approximately once a year, a leap second is introduced to Coordinated Universal Time.
References
R. A. Nelson, D. D. McCarthy, S. Malys, J. Levine, B. Guinot, H. F. Fliegel, R.L. Beard, & T. R. Bartholomew, The leap second: its history and possible future. Metrologia, vol. 38, no. 6, pp. 509-529, 2001
R. S. Gross, Earth Rotation Variations – Long Period, In T. A. Herring (Ed.) Treatise on Geophysics, Volume 11: Physical Geodesy, Amsterdam, Elsevier, 239-294, 2007
