The First Solar Flare
A solar flare is normally only visible when observing the Sun at a single wavelength. Most modern solar flare patrol is done by observing the Sun in the light of Hydrogen-alpha radiation at a wavelength of 656.3 nanometres. Occasionally, however, a very large flare will release sufficient energy to be visible in the unfiltered light from the Sun. It was such a white light event on September 1, 1859 that was the first solar flare ever to be recorded (to our knowledge) by humankind. Two independent observers, R C Carrington and R Hodgson, described their experiences in volume twenty of the Monthly Notices of the Royal Astronomical Society:
Description of a Singular Appearance seen in the Sun on September1, 1859. R C Carrington.
While engaged in the forenoon of Thursday, Sept. 1, in taking my customary observation of [...] the solar spots, an appearance was witnessed which I believe to be exceedingly rare. [...] I had secured diagrams of all the groups and detached spots, and was engaged at the time in counting [...] the spots [...] when within the area of the great north group (the size of which had previously excited general remarks), two patches of intensely bright and white light broke out. [...] I thereupon noted down the time by the chronometer, and seeing the outburst to be very rapidly on the increase, and being somewhat flurried by the surprise, I hastily ran to call some one to witness the exhibition with me, and on returning within 60 seconds, was mortified to find that it was already much changed and enfeebled. Very shortly afterwards the last trace was gone [...]
On a Curious Appearance seen in the Sun. R Hodgson.
While observing a group of solar spots on the 1st September, I was suddenly surprised at the appearance of a very brilliant star of light, much brighter than the Sun's surface, most dazzling to the protected eye, illuminating the upper edges of the adjacent spots and streaks, not unlike in effect the edging of the clouds at sunset; the rays extended in all directions; and the centre might be compared to the dazzling brilliancy of the bright star alpha-Lyrae when seen in a large telescope of low power. It lasted for some five minutes, and disappeared instantly about 11.25am. The phenomenon was of too short duration to admit of a micrometrical drawing, but an eye-sketch was taken [...] and [...] the size of the group appears to have been about [...] 60,000 miles. [...]
The authors also note that a magnetic disturbance was recorded simultaneously with the white light flare observation, and also that "towards four hours after midnight there commenced a great magnetic storm". The first recorded solar flare is thus probably also the first observed instance (and of course with one event, it could only be an indication), wherein a change on the Sun was believed to have directly influenced the environment around the Earth.
Below is a copy of Carrington's sketch to accompany his paper of 1860. This observation was made from Redhill, England. Points A,B,C, and D are believed to be the intense white flaring regions.
Material Prepared by John Kennewell.