Скачать или смотреть Neil deGrasse Tyson: Why a Day Isn’t 24 Hours

Neil deGrasse Tyson: Why a Day Isn’t 24 Hours

We often say that Earth completes one rotation in 24 hours, but that’s not entirely true. In reality, Earth spins once on its axis in 23 hours, 56 minutes, and 4 seconds. So why do our clocks run on 24 hours instead of 23:56?

Neil deGrasse Tyson explains the fascinating difference between sidereal time (measured by Earth’s rotation relative to the stars) and solar time (measured by the Sun’s position in the sky). Because Earth is also moving along its orbit while rotating, it needs to spin a little more—about 4 minutes—for the Sun to return to the same spot in the sky. That’s why our day is measured as 24 hours.

But there’s more: since Earth’s orbit is not a perfect circle, this difference is not always exactly 4 minutes. Sometimes the Sun appears up to 16 minutes ahead or 16 minutes behind the clock. To fix this, humans created an average system—and in English, “mean” means “average.” That’s where Greenwich Mean Time (GMT) comes from.

This story shows how astronomy, mathematics, and history combined to shape the way we experience time today. If you’re curious about space, science, Earth’s motion, and the origins of timekeeping, Neil deGrasse Tyson breaks it down in this fascinating explanation.
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