Corona near mid-totality
"Diamond ring" effect
at third contact
Photo's taken with mirror of 3,000mm focal length and 10.8cm aperture by W. Atkinson at Nantucket airport.
To describe the appearance (of the flash, spectrum) in 1870 one cannot do better than to quote from the words of the discoverer:
"The observation is possible only... at a total eclipse of the sun, at the moment when the advancing moon has just covered the sun's disc- the solar atmosphere [chromosphere] of course projects somewhat at the point where the last ray of sunlight [from the brilliant photosphere] has disappeared. If the spectroscope (visual in this case) be then adjusted with its slit tangent to the sun's image at the point of contact, a most beautiful phenomenon is seen. As the moon advances, making narrower and narrower the remaining sickle of the solar disc, the dark (Fraunhofer) lines of the spectrum for the most part remain sensibly unchanged, though becoming somewhat more intense. A few, however, begin to fade out, and some even turn palely bright a minute or two before totality begins. But the moment the sun is hidden, through the whole length of the spectrum, in the red, the green, the violet, the bright lines flash out by hundreds and thousands, almost startlingly, as suddenly as stars from a bursting rockethead, and as evanescent, for the whole thing is over in two or three seconds. The layer seems to be only something under a thousand miles in thickness, and the moon's motion covers it very quickly." (G. A. Young)
From the centerfold (pp.308-309) of "Sky and Telescope", May, 1970, Vol.
39, No. 5.
© Sky Publishing Corporation 1970
See also S+T issue cover photo (left panel) and article in "Gleanings for ATMs", A Slitless Spectrograph for the Flash Spectrum (pp.318-323)
Spectrograph- cover off revealing film plane and test spectrum
Parabolic film plane; focus test