Carrington rotations
Convert a date to its Carrington rotation number and back, and browse rotation start and end times.
CR 638
| Start | June 6, 1901 at 09:20 AM UTC |
|---|---|
| End | July 3, 1901 at 02:04 PM UTC |
| Length (days) | 27.20 |
Neighbouring rotations
| CR | Start | End | Length (days) |
|---|---|---|---|
| 633 | January 20, 1901 at 11:29 PM UTC | February 17, 1901 at 07:39 AM UTC | 27.34 |
| 634 | February 17, 1901 at 07:39 AM UTC | March 16, 1901 at 03:27 PM UTC | 27.33 |
| 635 | March 16, 1901 at 03:27 PM UTC | April 12, 1901 at 10:24 PM UTC | 27.29 |
| 636 | April 12, 1901 at 10:24 PM UTC | May 10, 1901 at 04:18 AM UTC | 27.25 |
| 637 | May 10, 1901 at 04:18 AM UTC | June 6, 1901 at 09:20 AM UTC | 27.21 |
| 638 | June 6, 1901 at 09:20 AM UTC | July 3, 1901 at 02:04 PM UTC | 27.20 |
| 639 | July 3, 1901 at 02:04 PM UTC | July 30, 1901 at 07:04 PM UTC | 27.21 |
| 640 | July 30, 1901 at 07:04 PM UTC | August 27, 1901 at 12:42 AM UTC | 27.23 |
| 641 | August 27, 1901 at 12:42 AM UTC | September 23, 1901 at 07:01 AM UTC | 27.26 |
| 642 | September 23, 1901 at 07:01 AM UTC | October 20, 1901 at 01:53 PM UTC | 27.29 |
| 643 | October 20, 1901 at 01:53 PM UTC | November 16, 1901 at 09:08 PM UTC | 27.30 |
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.