Celestial Navigation · Time — Sidereal vs Solar
A sidereal day (Earth's rotation relative to the stars) is, compared with a mean solar day:
- AExactly the same length
- BAbout 4 minutes shorter✓ Correct
- CAbout 1 hour longer
- DAbout 6 hours shorter
Explanation
Because the Earth also orbits the sun, it must rotate slightly more than 360° for the sun to return to the meridian, so the solar day is about 4 minutes longer than the sidereal day. This is why a given star rises about 4 minutes earlier each day.
Authority: Bowditch (Pub. No. 9), Time
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