Multiple choice general knowledge

The length of the tropical years (the time interval between successive occurrences of the spring equinox) is decreasing very slowly as a result of

  1. small, progressive changes in the earth's rotational speed

  2. small, progressive change in earth's orbit around the sun

  3. both (a) and (b)

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The tropical year (time between successive spring equinoxes) is slowly decreasing due to both gradual changes in Earth's rotational speed and small changes in Earth's orbit around the Sun. Earth's rotation is very gradually slowing due to tidal friction from the Moon, and orbital parameters undergo cyclical variations (Milankovitch cycles) including changes in eccentricity, axial tilt, and precession. These combined effects cause the measured tropical year length to decrease very slightly over long timescales.

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