Word of the Day

sidereal, adj.

Pronunciation:  /saɪˈdɪərɪəl/
Forms:  Also 16–18 siderial (16 syd-); 16–17 sydereal (16 sydereall), 17 sydireal.
Etymology:  < Latin sīdereus, < sīder- , sīdus constellation, star + -al suffix1.


 1. Of or relating to the stars.

1642   H. More Ψυχωδια Platonica sig. M7v,   Upon which pure bright sydereall phantasms unprejudiced reason may safely work.
1651   H. More Enthusiasmus Triumphatus (1712) 32   That a Man has a sydereal body besides this terrestrial which is joined with the Stars.
1692   J. Salter Triumphs Jesus 24   Display your Glories ye Syderial States.
1739   H. Coventry Lett. Philemon to Hydaspes iii. 76   [A] most expressive, as well as permanent Symbol of the Sidereal Splendors.
1792   Philos. Trans. (Royal Soc.) 82 26   Among the changes that happen in the sidereal heavens we enumerate the loss of stars.
1834   T. Carlyle Sartor Resartus i. iii. 7/2   What thinks Bootes of them, as he leads his Hunting Dogs over the Zenith in their leash of sidereal fire?
1870   H. Spencer Princ. Psychol. (ed. 2) I. i. vii. 137   That general Astronomy which includes our whole Sidereal System.
1874   F. W. Farrar Life Christ I. iii. 29   That any strange sidereal phenomenon should be interpreted as the signal of a coming king, was in strict accordance with the belief of their age.


 2. Star-like, lustrous, bright. rare.

1634   Bp. J. Hall Contempl. Hist. New Test. (STC 12640.5) 201   With what a blushing astonishment doth she behold his sydereall countenance cast upon her?
1649   Bp. J. Hall Humble Motion to Parl. 30   Provoking some sydereall and flaming soules to display themselves in their full..lustre.

 3. a. Of periods of time: determined or measured by means of the stars. sidereal day: the time between the successive meridional transits of a star, or specifically of the first point of Aries; about four minutes shorter than the solar day. Also sidereal month, sidereal year, sidereal time (see quots.).

1681   G. Wharton Disc. Years in Wks. (1683) 71   The Sydereal year is the space of time, in which the Sun returns to the same star from whence he departed.
1715   tr. D. Gregory Elements Astron. I. ii. §11. 242   The Astronomic [year] is also twofold,..namely, the Sydereal and Tropical. The Sydireal Year..is 365 Days, 6 Hours, and 10 Minutes nearly.
1794   G. Adams Lect. Nat. & Exper. Philos. IV. xlii. 156   There must be one more siderial day in a year than there are solar days.
1812   R. Woodhouse Elem. Treat. Astron. viii. 50   A clock regulated by the transit of fixed stars, or adapted to sidereal time.
1846   A. Young Naut. Dict. 95   The interval between the departure and return of a meridian to the sun is called a solar day; in the case..of a star, a sidereal day.
1868   J. N. Lockyer Elem. Lessons Astron. §434   The sidereal month is the interval between two successive conjunctions of the moon with the same fixed star.


 b. Of a clock: showing sidereal time.

1812   R. Woodhouse Elem. Treat. Astron. Pref.,   An observation expressed by..the seconds of a sidereal clock.


 4. Of planetary or lunar motion: relative to the stars.

1815   J. Smith Panorama Sci. & Art I. 554   Its annual sidereal revolution is calculated by Laplace, to be performed in 1681 days, 17 hours, 57 seconds.
1833   J. F. W. Herschel Astronomy viii. 252   The sidereal periods of the planets may be obtained..by observing their passages through the nodes of their orbits.
1868   W. Lockyer tr. A. Guillemin Heavens (ed. 3) 66 (note) ,   This revolution is called a sidereal revolution in contradistinction to the ‘synodic revolution’, because, relatively to the Sun, the planet again occupies the same portion of the heavens.


 5. Concerned with the stars.

1833   J. F. W. Herschel Astronomy 372 Chap. xii.   Of Sidereal Astronomy.
1853   J. F. W. Herschel Pop. Lect. Sci. (1873) v. §28. 204   Thus opening another chapter in the history of sidereal mensuration.
1870   tr. Pouchet's Universe (1871) 519   The nebulæ mark the limits of sidereal investigation.