On this page
Most mornings Richard Carrington did the same careful job: project the Sun's image, draw every spot, time each one against cross-wires. On 1 September 1859 that routine let him record something no one had described before, a solar flare. This post tells the story from his own report, works through the numbers in it, and shows why his caution about what it meant is as useful as the discovery.
Who was Richard Carrington?
The Royal Astronomical Society's obituary notice, printed in February 1876, records that he was born in Chelsea on 26 May 1826, entered Trinity College, Cambridge, in 1844 and graduated in 1848. His father hoped he would join the Church, but lectures by James Challis turned him to astronomy. After nearly three years as observer at Durham, he built his own observatory at Redhill.
There he catalogued 3,735 stars near the north celestial pole, each observed at least three times, published in 1857; the Society gave him its Gold Medal for 1859. In daytime he observed the Sun. From 9 November 1853 to 24 March 1861 he recorded the positions of sunspots and found that spots near the Sun's equator go round faster than spots at high latitude, with a difference of more than two days in rotation period between the equator and latitude 50°. The Sun does not rotate like a solid ball.
What did he see on 1 September 1859?
His report, Description of a Singular Appearance seen in the Sun on September 1, 1859, appeared in the Monthly Notices of the Royal Astronomical Society. He was projecting an image about 11 inches across when, within a large spot group, "two patches of intensely bright and white light broke out". His first thought was that light was leaking through a hole in his screen. Moving the telescope showed it was on the Sun.
He ran to call a witness and was back within 60 seconds, to find the patches "already much changed and enfeebled". He timed the start to within 15 seconds of 11h 18m Greenwich mean time and the end at 11h 23m. In those five minutes the patches moved about 35,000 miles. Richard Hodgson, observing at Highgate, saw it independently, and Carrington noted that he had avoided exchanging any information with him so the two accounts would stay independent.
The report of the meeting adds that magnetic instruments at Kew showed a short, marked disturbance at about 11h 20m, and that "towards four hours after midnight there commenced a great magnetic storm". Carrington refused to claim the two were linked: he "would not have it supposed that he even leans towards hastily connecting them", adding "One swallow does not make a summer."
How big was the storm, and what did India record?
A 2003 analysis in the Journal of Geophysical Research, The extreme magnetic storm of 1-2 September 1859, calls it the most intense storm in recorded history. Its abstract reports that the magnetic observatory at Colaba, in Mumbai, recorded a change in the horizontal field of 1,600 ± 10 nT, and argues that the flare probably launched a fast cloud of magnetised gas towards Earth. The authors also warn that a storm this strong, or stronger, may occur again.
Can you work with Carrington's numbers? A worked example
Use the NASA Sun fact sheet radius of 695,700 km (diameter 1,391,400 km) and 1 mile = 1.609 km.
Speed of the bright patches. 35,000 miles × 1.609 = 56,300 km in 5 minutes, or 300 s. Speed = 56,300 ÷ 300 ≈ 190 km/s.
Size on his drawing. 56,300 ÷ 1,391,400 ≈ 0.040, so the patches moved about 4% of the Sun's diameter. His diagram was drawn at 12 inches to the Sun's diameter, so that is 0.040 × 12 ≈ 0.49 inch, about 1.2 cm on paper.
Average speed if the flare caused the storm. From 11h 18m to about 4 a.m. the next day is roughly 16.7 hours, or 6.0 × 10⁴ s. Earth's distance from the Sun is 1.496 × 10¹¹ m (from the NASA Earth fact sheet), so the average speed would be 1.496 × 10¹¹ ÷ 6.0 × 10⁴ ≈ 2.5 × 10⁶ m/s, about 2,500 km/s.
Compare step 3 with the ordinary solar wind. Our post on Eugene Parker and the solar wind shows that a slow stream of about 350 km/s takes around five days to reach Earth. Something leaving the Sun at the moment of the flare and arriving 17 hours later had to be several times faster.
Common mistakes:
Leaving units mixed. Convert miles to km and minutes to seconds before dividing.
Using radius for diameter. The drawing scale is per diameter.
Treating step 3 as proof. It assumes cause and effect, which is exactly what Carrington would not assume. "Towards four hours" is also approximate, so the answer is only good to about 10%.
If unit conversions keep costing you marks, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer.
What happened to Carrington's work?
The obituary notes that in 1858 his father's death left him running the family brewery at Brentford, though he kept supervising the solar work and published the full sunspot results in 1863 with help from a Royal Society grant. Space weather is now watched closely from space; our post on Aditya-L1 covers India's own solar observatory.
What can a student take from Carrington's way of working?
Keep a routine. He saw the flare because he observed the Sun every clear day.
Write things down before you need them. The sketch made before the flare was his evidence that the spot group had not changed.
Get an independent check. He did not compare notes with Hodgson, so the two reports could confirm each other.
Do not overclaim. He noted the magnetic storm and still refused to connect them on one event.
Try it now: redo step 3 assuming the storm started at 2 a.m. instead, and see how much the speed changes.
