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What was the first method used to observe solar prominences without an eclipse?

I understand that Helium was first discovered in the Sun, separately by Pierre Janssen and Norman Lockyer, in 1868, discovering its spectral line at 588 nm and concluding that it might be from an unknown element.

They both used the solar eclipse of that year, I think, to observe the spectral line in a solar prominence, but both also later devised a method to observe solar prominences without an eclipse. Reference for Pierre Jannsen and reference for Norman Lockyer.

Currently, filters are recommended to observe solar prominences outside of an eclipse, was this the method that Lockyer and Janssen also used?

I looked up the original publication by Lockyer, but it does not mention if that observation was made during an eclipse.

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  • $\begingroup$ What about just occluding the main body of the Sun with an opaque disk? $\endgroup$ – probably_someone Jul 18 '17 at 7:12
  • $\begingroup$ I assume because scattered light from the main body overwhelms the signal. Also solar prominences were only seen during eclipses for hundreds of years (since 1185), I imagine someone would have thought of disks in that time. $\endgroup$ – mjeppesen Jul 18 '17 at 7:23
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I emailed a former Norman Lockyer Fellow at St Andrews, University, who thought that he would have used a coronagraph, which is basically a disk which blocks out the sun. Sky brightness is the problem which needed to be solved though. From Wikipedia:

Ground based coronagraphs, such as the High Altitude Observatory's Mark IV Coronagraph on top of Mauna Loa, use polarization to distinguish sky brightness from the image of the corona: both coronal light and sky brightness are scattered sunlight and have similar spectral properties, but the coronal light is Thomson-scattered at nearly a right angle and therefore undergoes scattering polarization, while the superimposed light from the sky near the Sun is scattered at only a glancing angle and hence remains nearly unpolarized.

Perhaps Lockyer and Janssen also used polarisation.

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