Astronomy of time (tropical year): The length of the tropical year (interval between successive spring equinoxes) is decreasing very slowly. This slow decrease primarily results from which long-term changes in Earth's motions? Choose the most accurate cause.
General Knowledge
World Geography
Difficulty: Easy
Choose an option
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ASmall, progressive changes in the Earth's rotational speed
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BSmall, progressive changes in Earth's orbit around the Sun
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CBoth (a) and (b)
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DNone of the above
Answer
Correct Answer: Both (a) and (b)
Explanation
Given data
- Tropical year is measured from equinox to equinox; subtle secular variations are observed.
Concept/ApproachVery small, long-term changes arise from orbital perturbations (e.g., precession, gravitational interactions) and from rotational changes (e.g., tidal friction slowly altering Earth's rotation rate). Together these contribute to tiny secular shifts in the tropical year.
Common pitfallsAttributing the effect to only one component; in reality, both orbital and rotational dynamics are involved.
Final AnswerBoth (a) and (b)