A Popular History of Astronomy During the Nineteenth Century: Fourth EditionClerke, Agnes M. (Agnes Mary)
History
A Popular History of Astronomy During the Nineteenth Century: Fourth Edition
Clerke, Agnes M. (Agnes Mary)
Astronomy -- History -- 19th century
But the leading, and a truly amazing, characteristic of the phenomenon
was formed by two vast, faintly-luminous _wings_ of light, expanded on
either side of the sun in the direction of the ecliptic. These were
missed by very few careful onlookers; but the extent assigned to them
varied with skill in, and facilities for seeing. By far the most
striking observations were made by Newcomb at Separation (Wyoming), by
Cleveland Abbe from the shoulder of Pike's Peak, and by Langley at its
summit, an elevation of 14,100 feet above the sea. Never before had an
eclipse been viewed from anything approaching that altitude, or under so
translucent a sky. A proof of the great reduction in atmospheric glare
was afforded by the perceptibility of the corona four minutes after
totality was over. For the 165 seconds of its duration, the remarkable
streamers above alluded to continued "persistently visible," stretching
away right and left of the sun to a distance of at least ten million
miles! One branch was traced over an apparent extent of fully twelve
lunar diameters, without sign of a definite termination having been
reached; and there were no grounds for supposing the other more
restricted.
The resemblance to the zodiacal light was striking; and a community of
origin between that enigmatical member of our system and the corona was
irresistibly suggested. We should, indeed, expect to see, under such
exceptionally favourable atmospheric conditions as Professor Langley
enjoyed on Pike's Peak, the _roots_ of the zodiacal light presenting
near the sun just such an appearance as he witnessed; but we can imagine
no reason why their visibility should be associated with a low state of
solar activity. Nevertheless this seems to be the case with the
streamers which astonished astronomers in 1878. For in August, 1867,
when similar equatorial emanations, accompanied by similar symptoms of
polar excitement, were described and depicted by Grosch[538] of the
Santiago Observatory, sun-spots were at a minimum; while the corona of
1715, which appears from the record of it by Roger Cotes[539] to have
been of the same type, preceded by three years the ensuing maximum. The
eclipsed sun was seen by him at Cambridge, May 2, 1715, encompassed with
a ring of light about one-sixth of the moon's diameter in breadth, upon
which was superposed a luminous cross formed of long bright branches
lying very nearly in the plane of the ecliptic, and shorter polar arms
so faint as to be only intermittently visible. The resemblance between
his sketch and Cleveland Abbe's drawing of the corona of 1878 is
extremely striking. It should, nevertheless, be noted that some
conspicuous spots were visible on the sun's disc at the time of Cotes's
eclipse, and that the preceding minimum (according to Wolf) occurred in
1712. Thus, the coincidence of epochs is imperfect.
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