sidereal

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?

The field of sidereal astronomy, therefore, was virtually untrodden when, shortly after the beginning of his telescopic work, Herschel began his first review of the heavens.

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.

Relating to a measurement of time relative to the point of the vernal equinox.