Total Solar Eclipse of March 7, 1970

Totality

 

Photos taken with mirror of 3,000mm focal length and 10.8cm aperture by W. Atkinson at Nantucket airport.


Flash Spectrum of the Solar Chromosphere

To describe the appearance (of the flash spectrum) in 1870 to accompany my own photo 100 years later (below, taken in 1970), one cannot do better than to quote from the words of the discoverer, Charles Augustus Young.

An excerpt from S. A. Mitchell’s Eclipses of the Sun, Columbia University Press, 1951, Pg. 104:

“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.” (C. A. Young).

From the centerfold (pp. 308-309) of Sky & Telescope, May, 1970, Vol. 39, No. 5. © Sky Publishing Corporation 1970

Flash Spectrum, March 7, 1970
The flash spectrum at the conclusion of totality (third contact) on March 7, 1970, by William C. Atkinson and Frank B. Dow, Jr.

Flash spectrum
The arcs are emission lines of the solar chromosphere, conspicuous ones being the D3 line of neutral helium in the yellow (between red and green) at 5876 angstroms and the H and K lines of ionized calcium at 3968 and 3934 in the violet (here rendered blue). The Balmer lines of hydrogen extend from Hà in the red (overexposed) at 6563… In the green at 5303 angstroms, the ringlike image is the corona itself in the light of iron atoms ionized 13 times. Chromospheric lines from within the ring are from the element magnesium.

Sky & Telescope

See also issue cover photo above (left panel at right) and article in “Gleanings for ATMs,” A Slitless Spectrograph for the Flash Spectrum (pp. 318-323).

This photograph appears in several astronomy text books (cf. Jay Pasachoff), in NASA’s A New Sun: The Solar Results from Skylab (Chapter 2, p. 31), Geo magazine, and was displayed in the “Hall of the Sun” at the Planetarium of the New York City Museum of Natural History—until its renovation ca. 1999.

(For the full story of my trip to Nantucket in March 1970, see this post: Astronomy, An Adventure.)


63072014_Spectrograph
Spectrograph by William C. Atkinson

Telescope construction in Weston on my father’s handmade maple workbench

70020020_FilmPlane
Carbon arc spectrum on film plane

70020017_Collimator

 

70020014_SpGraph

 

70020001_Mounting