Addendum 2020 to ‘Measurement of the Earth’s rotation: 720 BC to AD 2015’
L. V. Morrison, F. R. Stephenson, C. Y. Hohenkerk, M. Zawilski
Abstract
Historical reports of solar eclipses are added to our previous dataset (Stephenson et al. 2016 Proc. R. Soc. A 472 , 20160404 ( doi:10.1098/rspa.2016.0404 )) in order to refine our determination of centennial and longer-term changes since 720 BC in the rate of rotation of the Earth. The revised observed deceleration is −4.59 ± 0.08 × 10 −22 rad s −2 . By comparison the predicted tidal deceleration based on the conservation of angular momentum in the Sun–Earth–Moon system is −6.39 ± 0.03 × 10 −22 rad s −2 . These signify a mean accelerative component of +1.8 ± 0.1 × 10 −22 rad s −2 . There is also evidence of an oscillatory variation in the rate with a period of about 14 centuries.