Quiz question for solar observers

[Merlin66]

This is addressed to all solar observers.
Have you ever heard of "veiled sunspots"???
(I'm translating a French solar observing book at the moment and came across this reference)
I did find the (very interesting) answer...what do you think???
(The answer, if not found, will be given later)

[PeterM]

Hmmm nope.
To do with detailed sketches from French (religious?) astronomers in 1870s & 1880s. Maybe with some artistic licence thrown in? Representation of hell?
I haven't got a clue but looking forward to reading more.

[Merlin66]

Peter,
Getting close.....
But what does a "veiled sunspot" mean?

Any other suggestions???

[Saturnine]

I think that I've heard the term before but can't remember the explanation and not going to try guessing. Will wait for the answer,I could look it up but !!!

[AstroJunk]

I had to look it up :thumbsup:

[Merlin66]

Back in 1875 Father Secchi published his "Le Soleil". This was an up-to-date review of solar observing and solar knowledge.
He mentions, in Volume 1 his visual observations of sunspots.
He was convinced that he had seen the umbra of some sunspots covered by a faint pink veil of light. He includes many etchings of this phenomenon.


Notwithstanding his observations, this "pink veil" has not been recorded in modern times.
https://collection.crystalbridges.org/objects/2891/group-of-sun-spots-and-veiled-spots


A challenge to modern observers????

[astroron]

Link not available.
Error 521 Ray ID: 5b1918fcffb516e1 • 2020-07-12 07:37:12 UTC
Web server is down.
Cheers:thumbsup:

[Merlin66]

https://digitalcollections.nypl.org/items/510d47dd-e6c3-a3d9-e040-e00a18064a99
This should work.
I actually have a copy of Father Secchi’s book....I can scan the illustrations if needed.

[astroron]

Thanks Ken:thanx:
The pic came up just fine this time.
Very strange phenomenon indeed.:question:
Cheers:thumbsup:

[Merlin66]

Yeah, I can well understand why current solar observers may never have heard of “veiled sunspots”........

[N1]

Perhaps an artefact produced by the singlets/achromatic lenses they would have been using? It seems plausible that for the effect to become detectable, the umbra's image would have to be of a certain size, which would explain why only the bigger spot in the sketch has this feature.

[Merlin66]

Father Secchi discusses the possibility of archromatic artifacts (Le Soleil, Volume 1, pages 104-109) and concludes they are real - similar (in his words) to the pink flames seen at the edge of the moon's disk during totality.
There are four or five different illustrations (from 1866) which show the "voiles roses" in different sized sunspots.
I does seem strange that Newcomb's reference work " Popular Astronomy", 1892 nor the Flammarion & Gore "Popular Astronomy" circa 1900 fail to mention this phenomenon.
However, C.A.Young in his definitive "The Sun", 1882, does make mention (p117)
"....there are also fainter veils of a substance less brilliant, but sometimes rose-colored, which seem to float above the umbra."


He doesn't provide any further information or references.

[N1]

Hi Ken, so we don't know how exactly he concludes they are real e.g. based on positive evidence, or just based on his assessment that it's not CA?

Thinking about this some more - An AR's appearance differs greatly depending on the wavelength(s) it's observed at. So some visible light emanating from above the umbral regions is not entirely implausible. For example, part of a filament stretched across a sunspot's umbra (is that even possible?) may just be detectable if the area below is dark enough.

[Merlin66]

Mirko,
There's plenty of activity which can be observed in and around the sunspot umbra.
Light bridges, umbral spots are more obvious with G band (or Baader K-line) filters. You can also use a night-time Ha filter. Plenty of recorded data, but no record of "pink veils".
Secchi was convinced the pink glow was real.

[N1]

He also says the glow was similar to that of the prominences during a total eclipse, so it may very well result from emission at H alpha wavelengths.