Carrington rotations
Convert a date to its Carrington rotation number and back, and browse rotation start and end times.
CR 1660
| Start | September 30, 1977 at 11:30 AM UTC |
|---|---|
| End | October 27, 1977 at 06:27 PM UTC |
| Length (days) | 27.29 |
Neighbouring rotations
| CR | Start | End | Length (days) |
|---|---|---|---|
| 1655 | May 17, 1977 at 08:27 AM UTC | June 13, 1977 at 01:21 PM UTC | 27.20 |
| 1656 | June 13, 1977 at 01:21 PM UTC | July 10, 1977 at 06:06 PM UTC | 27.20 |
| 1657 | July 10, 1977 at 06:06 PM UTC | August 6, 1977 at 11:14 PM UTC | 27.21 |
| 1658 | August 6, 1977 at 11:14 PM UTC | September 3, 1977 at 05:02 AM UTC | 27.24 |
| 1659 | September 3, 1977 at 05:02 AM UTC | September 30, 1977 at 11:30 AM UTC | 27.27 |
| 1660 | September 30, 1977 at 11:30 AM UTC | October 27, 1977 at 06:27 PM UTC | 27.29 |
| 1661 | October 27, 1977 at 06:27 PM UTC | November 24, 1977 at 01:48 AM UTC | 27.31 |
| 1662 | November 24, 1977 at 01:48 AM UTC | December 21, 1977 at 09:31 AM UTC | 27.32 |
| 1663 | December 21, 1977 at 09:31 AM UTC | January 17, 1978 at 05:34 PM UTC | 27.34 |
| 1664 | January 17, 1978 at 05:34 PM UTC | February 14, 1978 at 01:45 AM UTC | 27.34 |
| 1665 | February 14, 1978 at 01:45 AM UTC | March 13, 1978 at 09:39 AM 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.