What factor determines the *duration* of Venus's visibility window in the twilight, separate from orbital mechanics?

Answer

The tilt of the Earth's axis relative to the Sun, which affects the ecliptic inclination.

While the orbital mechanics determine *when* Venus is visible (Evening or Morning Star), the *length* of time it stays visible after sunset or before sunrise is heavily influenced by seasonal factors related to Earth's orientation. Specifically, the tilt of the Earth's axis relative to the Sun dictates how steeply the ecliptic plane intersects the horizon at a given location and season. A very steep angle causes Venus to drop below the horizon quickly. A shallower angle allows the planet to linger longer in the western twilight, leading to observation periods that vary in duration even if the maximum elongation angle is similar across different viewing cycles.

What factor determines the *duration* of Venus's visibility window in the twilight, separate from orbital mechanics?

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