Carrington rotations
Convert a date to its Carrington rotation number and back, and browse rotation start and end times.
CR 910
| Start | September 28, 1921 at 01:19 AM UTC |
|---|---|
| End | October 25, 1921 at 08:15 AM UTC |
| Length (days) | 27.29 |
Neighbouring rotations
| CR | Start | End | Length (days) |
|---|---|---|---|
| 905 | May 14, 1921 at 10:22 PM UTC | June 11, 1921 at 03:19 AM UTC | 27.21 |
| 906 | June 11, 1921 at 03:19 AM UTC | July 8, 1921 at 08:03 AM UTC | 27.20 |
| 907 | July 8, 1921 at 08:03 AM UTC | August 4, 1921 at 01:08 PM UTC | 27.21 |
| 908 | August 4, 1921 at 01:08 PM UTC | August 31, 1921 at 06:54 PM UTC | 27.24 |
| 909 | August 31, 1921 at 06:54 PM UTC | September 28, 1921 at 01:19 AM UTC | 27.27 |
| 910 | September 28, 1921 at 01:19 AM UTC | October 25, 1921 at 08:15 AM UTC | 27.29 |
| 911 | October 25, 1921 at 08:15 AM UTC | November 21, 1921 at 03:34 PM UTC | 27.30 |
| 912 | November 21, 1921 at 03:34 PM UTC | December 18, 1921 at 11:15 PM UTC | 27.32 |
| 913 | December 18, 1921 at 11:15 PM UTC | January 15, 1922 at 07:17 AM UTC | 27.33 |
| 914 | January 15, 1922 at 07:17 AM UTC | February 11, 1922 at 03:29 PM UTC | 27.34 |
| 915 | February 11, 1922 at 03:29 PM UTC | March 10, 1922 at 11:24 PM UTC | 27.33 |
About this tool
A Carrington rotation is the time the Sun takes to turn once on its axis as seen from the Earth: 27.2753 days on average. The count was defined by the English astronomer Richard Carrington, who studied sunspots in the 1850s; rotation 1 began on 9 November 1853, and the numbering has run without interruption since.
Explorer computes the start of each rotation with the formula given by Jean Meeus in Astronomical Algorithms (chapter 29), implemented in its own astronomy library and checked against published dates. A rotation begins when the Carrington longitude L₀ of the central meridian passes through 0°; because the Earth moves along its orbit, the synodic period varies slightly around the mean, hence lengths of 27.2 to 27.3 days.
Observers use the rotation number as a calendar for the Sun: an active region that crosses the disc reappears about one rotation later, and the community activity heatmap shows one row per rotation so that returning regions line up. Enter a date to find its rotation, or a number to get the UTC start and end dates and the neighbouring rotations.