sideral

Adjective

sidereal (not comparable)

1. Of or relating to the stars.
   • These fringes of lamplight, struggling up through smoke and thousandfold exhalation, some fathoms into the ancient reign of Night, what thinks Boötes of them, as he leads his Hunting-Dogs over the Zenith in their leash of sidereal fire?1831, Thomas Carlyle, “Reminiscences”, in Sartor Resartus: The Life and Opinions of Herr Teufelsdröckh. […], London: Chapman and Hall, […], →OCLC, 1st book, page 14
2. Relating to a measurement of time relative to the position of the stars.
   • Then, from a sufficient number of observations of synodic periods to give their mean, we obtain the sidereal period, or period with reference to the stars.1903, Percival Lowell, “Chapter I”, in The Solar System
3. Relating to a measurement of time relative to the point of the vernal equinox.