Astronomical Theory Section - Planetary Phenomena


The Stability of the Earth's Obliquity  (5)

  • Introduction
  • Basic principles
  • Application to the Earth
  • Nutation
  • Practical consequences of precession and nutation
  • The influence of the planets
    • Interactions and beats
  • The stability of other planets
    • Mars
    • Venus
  • Interim Summary
  • The influence of the Moon
    • The future stability of the Earth-Moon system
  • Final Summary
This article firstly establishes the basic principles of stability before undertaking a detailed exploration of the phenomenon of precession, whereby the pointing direction of the spin axis varies with time. A mathematically rigorous analysis of the Earth-Moon-Sun system is then developed, leading to a calculation of numerical values for the precession and nutation of the Earth. The influence of the planets is next considered, where the similarity between the precession period of the Earth and the timescales of the planetary influences is able to produce significant variations in the obliquity. This analysis is repeated for the very different cases of Mars and Venus, and finally, to investigate the assertion that the presence of the Moon stabilises the Earth's obliquity, the analysis is carried out both for a fictitious Earth which never had a moon and the present situation extrapolated into the future.

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