Convert Hours to Sidereal Days

Convert Hours (h) to Sidereal Days (sid.d) instantly and accurately.

Conversion Formula

sid.d = h × 0.04178074624

About Hours

An hour (h) = exactly 3,600 s. The 24-hour day traces to ancient Egypt (10 daylight hours + 2 twilight + 12 night star-rise periods). Time zones are integer or half-hour UTC offsets (exceptions: India +5:30, Nepal +5:45). The kilowatt-hour = 3,600,000 J; Tc-99m half-life = 6.0067 h. Drug dosing and pharmacokinetics are expressed in hours. 1 h = 3,600 s = 60 min = 1/24 day.

About Sidereal Days

A sidereal day = Earth's rotation period relative to the stars = 23 h 56 min 4.0905 s = 86,164.0905 s - ~3 min 56 s shorter than the 24 h solar day because Earth advances ~1° in its orbit each day. Equatorial telescope mounts rotate at one turn per sidereal day to track stars. VLBI, GPS orbit determination, and polar-motion monitoring use sidereal rotation as their reference. 1 sid. day = 86,164.0905 s.

Quick Reference Table

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