Science · 6 pages · 12 min
Why a day is not exactly twenty-four hours of star time
A clock day follows the Sun, while the stars return about four minutes sooner.
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From the opening
A clock day of twenty-four hours is a mean solar day, the average time from noon to the next noon. The stars return to the same place in the sky sooner, in a sidereal day of about twenty-three hours and fifty-six minutes. The opening covers solar noon versus star return, why the orbit adds a turn, and why true noon still wanders.
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Inside
- Solar noon versus star return
- Why the orbit adds a turn
- Why true noon still wanders
- Why telescopes follow the stars
- Where the idea stops applying
- A distinction worth keeping
Sources
- The solar day and the sidereal day
- Mean solar time as the civil average