Merriam-Webster Logo
  • Dictionary
  • Thesaurus
  • Scrabble
  • Spanish Central
  • Learner's Dictionary

sidereal day


Definition of sidereal day

  1. :  the interval between two successive transits of a point on the celestial sphere (as the vernal equinox) over the upper meridian of a place :  23 hours, 56 minutes, 4.1 seconds of mean time


First Known Use of sidereal day


Learn More about sidereal day

Seen and Heard

What made you want to look up sidereal day? Please tell us where you read or heard it (including the quote, if possible).