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Sun-Earth Day Presents: Eclipse, In a Different Light

Astronomers of the 1800's observed and catalogued nearly all of the solar features we know about today, including the rare coronal mass ejection seldom seen without special equipment.


Drawing of the 1860 eclipse by G. Tempel

Drawing of the 1860 eclipse by G. Tempel

Since the 1970's, astronomers have studied brief explosions of matter in the solar corona which were at one time called 'coronal transients'. Thanks to satellite observatories such as SMM and Skylab, these transients were quickly found to be complex and spectacular eruptions of matter, now called coronal mass ejections or CMEs. We commonly mark the advent of the discovery of these events with the observations made during the modern satellite era, but this may not be a fair assessment of past historical events.

The total solar eclipse of 18 July 1860 was probably the most thoroughly observed eclipse up to that time. What is unusual about this eclipse is that, unlike most drawings of the solar corona up until that time, the drawings of the 1860 eclipse all show a peculiar feature in the southwest (lower right) portion of the corona. Most coronal sketches captured the radial 'rays' and other linear features that seem to delineate the corona. They also show from time to time, prominences and loops near the limb of the sun, which were a keen interest among telescopic observers. However, the 1860 eclipse was unique in that the outer reaches of the corona were not uniform, but possessed their own unusual structures. The feature drawn repeatedly by a variety of skilled astronomers was unlike anything seen before in these solar hinterlands.

SOHO CME photograph

A coronal mass ejection observed by the SOHO satellite, similar to the one sketched in 1860.

Based on a comparison with modern coronal observations such as the one obtained by the SOHO satellite, is quite likely that these drawings are nothing less than the first record of a Coronal Mass Ejection in progress.

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