How long is earth's rotation?

Earth rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes, and 4 seconds with respect to the stars (see below). Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. read more

Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86,164.098 903 691 seconds of mean solar time (UT1) (23 h 56 m 4.098 903 691 s, 0.997 269 663 237 16 mean solar days). read more

Earth’s rotation period relative to the precessing or moving mean vernal equinox, meanwhile, is 23 hours 56 minutes and 4.0905 seconds of mean solar time. Not a major difference, but a difference nonetheless. However, the planet is slowing slightly with the passage of time, due to the tidal effects the Moon has on Earth’s rotation. read more