gen-explain-the-tropical-year-length-as-you-would-to-a-capable-s-5fb3

Explain the tropical year length as you would to a capable student, in 3-4 sentences.

A tropical year is the time it takes Earth to complete one full cycle of seasons—from one spring equinox back to the next spring equinox—which is about 365.24219 days. This is slightly shorter than the time it takes Earth to orbit the sun relative to distant stars (the sidereal year) because Earth's axis slowly wobbles in a motion called precession, causing the equinoxes to drift backward about 20 minutes per year. This 365.24219-day length is why we need leap years: we use 365 days in our calendar, then add an extra day every four years (with some exceptions) to keep our calendar aligned with the seasons. Without this correction, our calendar would gradually drift out of sync with the seasons over centuries.