Protuberance approach vs. Coronograph

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Protuberance approach vs. Coronograph

Post by Solar-Cologne »

Hello Sun Enthusiasts,

I've read here in a few of your posts more often: "I used a coronographer".
But I see pictures of prominences.

This is not correct.

So you used a prominence approach.

A coronographer shows an artificial sun corona !

https://en.wikipedia.org/wiki/Coronagraph

https://translate.google.com/translate? ... rev=search

sunny Greetings
Achim


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Re: Protuberance approach vs. Coronograph

Post by Solar-Cologne »

Coronograph,

special telescope according to B. Lyot for observation and photography of the corona in the darkened sun. Since the surface brightness of the sun disk is 106 times greater than that of the corona, an artificial eclipse is carried out in the coronograph. For this purpose, a picture of the sun is designed with a simple lens and the sun disk is reflected in it by a conical diaphragm on the tube wall in such a way that it no longer disturbs the view. To avoid stray light, the lens used in the coronograph must obey the highest quality criteria and the interior of the instrument must also be evacuated.

An observation of the corona is only possible if the light scattering of suspended dust particles in the atmosphere is reduced to a minimum. For this reason, the coronographers are used in the high mountains. They are also used in space telescopes.
Coronograph.jpg
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Basic structure of the protuberance approach to Lille

With a protuberance approach, the amateur opens up a completely new field of observation and activity. The light falls from the telescope lens directly onto the cone. There, the sun's surface is hidden by the cone, so that only the edge of the sun is visible. The focal point is shifted back to the iris by the lens that holds the cone. The iris is then closed to such an extent that the scattered light generated by the lens edge is masked out. The projection lens depicts the new image in the focal point f. Before that, the light falls through a narrow-band H-alpha filter. The H-Alpha filter is a very narrow-band interference filter with a pass band of 1.5 angstroms. The focus can then either be observed visually with an eyepiece or photographed with a camera.
protuberance approach to Lille.jpg
protuberance approach to Lille.jpg (46.66 KiB) Viewed 9489 times
sunny Greetings
Achim


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Re: Protuberance approach vs. Coronograph

Post by DeepSolar64 »

Does anyone make a coronagraph commercially? One an amateur could afford? I have read of amateurs making them well enough to see prominences but not the corona itself. I knew of the atmospheric scattering issue and know one would have to use a high mountaintop. Probably one high enough to require oxygen.

If only total solar eclipses weren't so rare.


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Re: Protuberance approach vs. Coronograph

Post by Montana »

I have one which was refurbished by Wolfgang

ImageBaader Corongraph is back! by Alexandra Hart, on Flickr

The tweezers and gloves are because you mustn't touch the cones (get grease on them).

ImageBaader Corongraph is back! by Alexandra Hart, on Flickr

ImageBaader Coronagraph by Alexandra Hart, on Flickr

Image2017-06-17 by Alexandra Hart, on Flickr

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Re: Protuberance approach vs. Coronograph

Post by Solar-Cologne »

Hello Alexandra,

Very very nice....But it is a Protuberance approach....not a Coronograph !

Achim


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Re: Protuberance approach vs. Coronograph

Post by christian viladrich »

Hi guys,

Detecting the corona is extremely difficulty. I've never heard of an amateur taking a corona image ...except during eclipses ;-)

Professionals used emission lines line (e.g. green line or near IR at the Pic du Midi) to "see" the E-corona ("E" stands for "emissions") or polarizers (e.g. K-cor in Hawai) the "see" the K-orona ('K" stands for continuum).
Detecting the "white light" corona (i.e. with no filter at all) is extremely challenging even for professionals.

Coronagraphs are also used to image planets arround stars. So basically, I would think that the use of the word "coronagraph" to block the solar disk image and see the prominences is correct.

As an historical note, the "Lyot diaphragm" was one of the big breakthroughs made by Bernard Lyot. Its purpose is to block part of the light diffracted by the main objective of the telescope. This is a form of "apodisation" reducing the diffraction rings arround the Airy disk.

In any case, viewing prominences with a coronagraph is quite spectacular ! This is great you make this type of equipement still available to the amateur.
Last edited by christian viladrich on Fri Apr 03, 2020 8:14 am, edited 1 time in total.


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Re: Protuberance approach vs. Coronograph

Post by marktownley »

I wasn't aware of the difference. Everyday is a school day!


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Re: Protuberance approach vs. Coronograph

Post by Montana »

It is a corongraph for observing prominences. You would never see the corona itself with it, only a solar eclipse or SOHO can see that :) but it still uses the cones of different sizes to obstruct the Sun so that you can see the prominences without an eclipse :)

Alexandra


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Re: Protuberance approach vs. Coronograph

Post by Solar-Cologne »

Hello Christian and Alexandra,

Please read my Post from 05:08 am

This article is from " Spectrum of science"

https://www.spektrum.de/lexikon/physik/koronograph/8382

Alexandra,

On your Baader approach is written in German .... Solar Prominence Viewer.

It means a Protuberance approach.



Best Regards
Achim


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Re: Protuberance approach vs. Coronograph

Post by christian viladrich »

Hello Achim,
Thanks for your link. For some reasons, I can see only the first page of the article.
For information, the original papers of Bernard Lyot are very interesting. They were presented in the french magazine "L'Astronomie".
I am not sure an English translation is available.


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Re: Protuberance approach vs. Coronograph

Post by Spectral Joe »

This is a subject that has irked me for a long time. I've carried a $100 bill in my wallet for more than 20 years, a prize for the first amateur telescope maker that can show me the corona in their "coronagraph". Not that it's impossible, if Lyot could do it in the 1930's it's easier now with improved manufacturing technology.

What's behind this use of the term "coronagraph" to describe an occulted and filtered telescope for viewing prominences? Three factors that I can account for, and there may be more. First is an article in the September 17, 1945 issue of Life magazine entitled "The Coronagraph" which featured Harvard's Climax station in Colorado. The article features images of prominences and implies this is the purpose of the instrument, presumably the editors realized that Life readers would not be impressed by images of the corona since it's just a blob in their minds. Second is an article in Scientific American's Amateur Scientist column, ten years later in September, 1955. This featured a "coronagraph" made by Walter Semerau, a well known and accomplished amateur astronomer in the Buffalo, NY area. Although a masterful piece of construction, it still couldn't perform the function of a coronagraph but probably fixed the definition in many minds. Third is the natural tendency of amateur astronomers to want their equipment to be as much like the professional variety as possible. Another example of this is referring to the diagonal mirror in a Newtonian telescope as the "secondary". Terms such as primary, secondary, tertiary, etc. are used in optical design to describe elements that contribute to image formation. A flat mirror (or prism) that diverts a beam doesn't get such a designation, but using the term for the diagonal might give the "mere Newtonian" an extra boost toward a catadioptric like a Cassegrain and make people feel better.

To sum up, a coronagraph is for imaging the corona, be the first to show me the corona in one that you built and you get a portrait of Ben Franklin worth $100. No joke.

Joe


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Re: Protuberance approach vs. Coronograph

Post by christian viladrich »

Hi Joe,

It could be that your $100 stay in your pocket for many more years :-)

Still, it could be feasible for an amateur to take up the challenge. Here is what would be needed :

(1) A 2800 high observing site.
(2) A 80 to 100 mm coronagraph is probably a good aperture since you need to pack everything in the car to get to the 2800 m high site.
The main lens is to be a superpolished plano-convex singlet. This part is quite feasible.
(3) Choice of filter :
- the Fe XIV line at 530.3 nm is the best choice (the contrast between corona and the sky is maximum),
- Fe XIII line at1074 nm is also feasible, but would need an IR camera,
- polarizers in combination of a red filter : probably much more difficult than green line.

All of this is feasible ;-)

BTW, a Ha filter is of no use for observation of the corona.The main emission lines of the corona being Fe XiV, Ca XV and Fe X.

Christian


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Re: Protuberance approach vs. Coronograph

Post by marktownley »

Go on then Christian, see if you can take the hundred bucks ;)


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Re: Protuberance approach vs. Coronograph

Post by christian viladrich »

Nope ... too much effort...
Indeed, a dear friend (who is an expert on solar corona) had tried to have me built a mirror coronagraph (a mirror as some advantages compared to a lens).
Well, I stick to the good old prominences with an Ha filter ;-)


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Re: Protuberance approach vs. Coronograph

Post by marktownley »

Sounds like your hundred bucks is safe Joe ;)


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Re: Protuberance approach vs. Coronograph

Post by Carbon60 »

Sounds like a good plan, Christian...... sticking to imaging Ha proms ;)

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Re: Protuberance approach vs. Coronograph

Post by MERRILL »

Very interesting!
1.5A interference filter is not suitable for mirror coronagraph.
Perhaps 10~5A filter OK.
But It's difficult to get one. Some amateur spent about EURO3000.
I seeking cheap filter recently.
I am merrill55=MERRILL.


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Re: Protuberance approach vs. Coronograph

Post by GreatAttractor »

Solar-Cologne wrote: Fri Apr 03, 2020 5:08 am Since the surface brightness of the sun disk is 106 times greater than that of the corona
Ha, I've just noticed this. Better to clarify, lest some reader thinks "so what's the big deal with imaging it" ;)

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Re: Protuberance approach vs. Coronograph

Post by DeepSolar64 »

All,
Discussing coronagraphs I remembered the K-Cor Coronagraph on the summit of Mauna Loa at the solar observatory located there. It is probably the only ground based coronagraph that I can think of that clearly shows the inner solar corona. It is a white light coronagraph.

This is the image for April 21. 2020

James

K Cor Coronagraph_WL_Mauna Loa.JPG
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Re: Protuberance approach vs. Coronograph

Post by MERRILL »

Fantastic !!


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