What is "sidereal hour"

Hour \Hour\, n. [OE. hour, our, hore, ure, OF. hore, ore, ure, F. heure, L. hora, fr. Gr. ?, orig., a definite space of time, fixed by natural laws; hence, a season, the time of the day, an hour. See Year, and cf. Horologe, Horoscope.]

1. The twenty-fourth part of a day; sixty minutes.

2. The time of the day, as expressed in hours and minutes, and indicated by a timepiece; as, what is the hour? At what hour shall we meet?

3. Fixed or appointed time; conjuncture; a particular time or occasion; as, the hour of greatest peril; the man for the hour.

   Woman, . . . mine hour is not yet come.
   --John ii.

4. This is your hour, and the power of darkness.
   --Luke xxii. 53.

   4. pl. (R. C. Ch.) Certain prayers to be repeated at stated times of the day, as matins and vespers.

5. A measure of distance traveled. Vilvoorden, three hours from Brussels. --J. P. Peters. After hours, after the time appointed for one's regular labor. Canonical hours. See under Canonical. Hour angle (Astron.), the angle between the hour circle passing through a given body, and the meridian of a place. Hour circle. (Astron.)

   1. Any circle of the sphere passing through the two poles of the equator; esp., one of the circles drawn on an artificial globe through the poles, and dividing the equator into spaces of 15[deg], or one hour, each.

   2. A circle upon an equatorial telescope lying parallel to the plane of the earth's equator, and graduated in hours and subdivisions of hours of right ascension.

   3. A small brass circle attached to the north pole of an artificial globe, and divided into twenty-four parts or hours. It is used to mark differences of time in working problems on the globe. Hour hand, the hand or index which shows the hour on a timepiece. Hour line.

      1. (Astron.) A line indicating the hour.

      2. (Dialing) A line on which the shadow falls at a given hour; the intersection of an hour circle which the face of the dial.

         Hour plate, the plate of a timepiece on which the hours are marked; the dial.
         --Locke.

         Sidereal hour, the twenty-fourth part of a sidereal day.

         Solar hour, the twenty-fourth part of a solar day.

         The small hours, the early hours of the morning, as one o'clock, two o'clock, etc.

         To keep good hours, to be regular in going to bed early.

n. 1/24 of a sidereal day