Carrington rotation number

Carrington rotation number

(ka -ring-tŏn) A sequential number, introduced by R.C. Carrington, that identifies each solar rotation. Its starting date is 1853 November 9.489 (rotation 1). The number is based on the value of 27.2753 mean solar days that Carrington obtained for the mean synodic rotation period of the Sun from observations of sunspots. This value is equivalent to the Sun having a mean sidereal rotation period of 25.380 mean solar days.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

Carrington rotation number

[′kar·iŋ·tən rō′tā·shən ‚nəm·bər]
(astronomy)
A method of numbering rotations of the sun based on a mean rotation period of sunspots of 27.2753 days, and starting with rotation number 1 on November 9, 1853.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.