Constants library

5 values, each with its units, its uncertainty, and where it came from.

Astronomical 5

T_{\mathrm{sid}} = 86164.0905\ \text{s}

sEarth's rotation period relative to the fixed stars, 23 h 56 min 4.09 s — about four minutes shorter than the solar day.

d = 86,400\ \text{s}

sThe civil day of exactly 86 400 SI seconds — a defined unit that Earth's actual rotation now overruns by a millisecond or two.

a_{\mathrm{J}} = 31,557,600\ \text{s}

sExactly 365.25 days of 86 400 SI seconds — the conventional astronomical year that defines the light-year and the Julian century.

T_{\mathrm{sid}}^{\mathrm{yr}} = 31558149.8\ \text{s}

sOne orbit of the Sun relative to the fixed stars, 365.2564 days — about 20 minutes longer than the tropical year of the seasons.

T_{\mathrm{trop}} = 31556925.2\ \text{s}

sEquinox to equinox, 365.2422 days — the year the seasons follow, and the quantity every calendar reform has tried to approximate.