Corona from 24 September 2022

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Corona from 24 September 2022

Post by george9 »

Here is a view from Pennsylvania last Saturday at 2300 feet on a very clear day. This is my 50mm coronagraph, 5303A filter, ASI1600 Pro camera, 60 sec video. The second image is a blowup of the biggest area. You can easily see the loop structures. At bottom in yellow is the SDO 171A satellite image to confirm the structures. The loops in the bigger structure match approximately, but the two images were not simultaneous, so there is some difference. There are still several aberrations I need to address, like the fringe and the arc of light off the surface.

George
2022-09-24-1822_8-CapObj_Planet_50_Sharp75_B129.0_C4.0_S1_N100 copy.jpg
2022-09-24-1822_8-CapObj_Planet_50_Sharp75_B129.0_C4.0_S1_N100 copy.jpg (124.87 KiB) Viewed 1833 times
2022-09-24-1822_8-CapObj_Planet_50_Sharp75_B129.0_C4.0_S1_N100 copy closeup2.jpg
2022-09-24-1822_8-CapObj_Planet_50_Sharp75_B129.0_C4.0_S1_N100 copy closeup2.jpg (181.84 KiB) Viewed 1833 times
SDO small 20220924_182646_2048_0171.jpg
SDO small 20220924_182646_2048_0171.jpg (156.15 KiB) Viewed 1833 times


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

George,
I have always felt that capturing anything of the corona is the holy grail of amateur solar astronomy. You had trod where few amateurs have. You are in a small group who have. My home here in the western North Carolina mountains is at about 2.200 feet asl.

Congratulations! I would like to see more of your work here especially as we continue to get closer to solar maximum.

👍🏻👍🏻 James


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Re: Corona from 24 September 2022

Post by MAURITS »

Nice to see George.


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Re: Corona from 24 September 2022

Post by christian viladrich »

Splendid George !!


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Re: Corona from 24 September 2022

Post by Sergio Alessandrelli »

Great image!


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Re: Corona from 24 September 2022

Post by ffellah »

Excellent!

Franco


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Re: Corona from 24 September 2022

Post by george9 »

Thanks very much. I will point out that I learned how to do it from Klaus160. And Christian's book was helpful with its easy-to-use formulas for the optical design. (And we all owe Lyot.) The hard part was debugging all the stray light in the system.

George


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

I haven’t seen Klaus on here for awhile. I hope he’s ok. I do remember his coronagraphy.

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Re: Corona from 24 September 2022

Post by hk160 »

> I haven’t seen Klaus on here for awhile. I hope he’s ok. I do remember his coronagraphy.

Alive and well - just really busy and Summer is not Corona season. I appreciate you asking though!

Also, I visited George that day at Cherry Springs since I live close by, but I had to leave around noon before he took the images. I did see the Corona in my 1" though that day as well from there.

Great pictures from George! Probably the best of any amateur instrument yet. This shows the quality of the instrument, but also of his new camera and the stacking. I am looking forward to George using his combination under even better conditions, as the sky was good, but certainly not as good as what I had seen on Mt. Mitchell.


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

Nice to see you on here again Klaus. I am glad you are alive and well. Winter is coming and maybe you will get some good corona views.


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Re: Corona from 24 September 2022

Post by Alun_H »

Fantastic images George,thank you for sharing.

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Re: Corona from 24 September 2022

Post by Dennis »

Super interesting. Pls share more.


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Re: Corona from 24 September 2022

Post by Carbon60 »

Fantastic result. Presumably the sky clarity has to be excellent, not ‘milky’ blue, as is usually the case here on a sunny day.

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Re: Corona from 24 September 2022

Post by george9 »

Thanks. Yes, the sky has to be pretty clear. Just put the Sun behind an object, usually your thumb, and see if you can tell the Sun is hidden due to local sky brightening. If the sky looks deep blue to the edge of the Sun, you have a good day.

I cannot find a SC post of my most recent coronagraph, but here are some photos of it on CloudyNights:

https://www.cloudynights.com/topic/8178 ... hristened/

Also, excuse the cross posting, but here is what I am currently debugging. (Klaus and Christian already commented.)

For the fringes in the original photo: When I rotate the camera, the fringes stay oriented with the filters, not the camera, so I think it is the filters. In the eyepiece, I really don't see the fringes, but that may be because they are too dim, not because they are not there. These are each 1-second exposures with a 60-second video.

I tried rotating the two 5303 filters will respect to each other with no improvement. I will try tilting one, removing one, and also removing a couple of other filters because my train also has an old Meade green CCD filter and a UV-IR cut filter. They are mainly there to hold the heat in the homemade oven. The Meade also stops a very minor red leak that is seen when the 5303 filter is single stacked. I will also separate the two 5303 filters more.

I had the odd effect that if I am within something like 5 degrees of the Sun, I get the fringes. Further away they disappear. And there is a point where half the field is sharply divided into fringes and no fringes. Some photos are attached. I assume that means the Sun is getting down there, but when I disassemble the coronagraph piece by piece, back to front, I cannot find the Sun actually making its way down. It just reflects off the interior side of the optical tube. And tilting the scope slightly this way or that does not produce anything like a sharp line.

In the images below you can see a second dimmer fringe pattern superimposed. I think that is Newton's rings, which were predominant until I tilted the camera. And they do track the camera when I rotate it, making it clear that they are the Newton's rings. Plus they are more curved like Newton's rings.

There is also an arc of light in the original image. It disappears when the Sun is away from the edge, so a larger cone will solve it, but I will also lose some bright corona. I will work on that one, too.

George
Attachments
Full fringe 2022-09-24-1926_3-CapObj_0005 copy.jpg
Full fringe 2022-09-24-1926_3-CapObj_0005 copy.jpg (39.93 KiB) Viewed 1672 times
Half fringe 2022-09-24-1927_2-CapObj_0005 copy.jpg
Half fringe 2022-09-24-1927_2-CapObj_0005 copy.jpg (26.06 KiB) Viewed 1672 times
No fringe 2022-09-24-1925_8-CapObj_0000 copy.jpg
No fringe 2022-09-24-1925_8-CapObj_0000 copy.jpg (21.01 KiB) Viewed 1672 times


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

Nice coronagraph George. I wanna see Alexandra make a true coronagraph outta her Baader prominence viewer. Take out the ha filter and add a green filter.


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Re: Corona from 24 September 2022

Post by DavidP »

Fantastic work. Congratulations.


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Re: Corona from 24 September 2022

Post by george9 »

Here is a CN post that describes converting a Baader prominence viewer to a coronagraph: https://www.cloudynights.com/topic/7888 ... p=11357452

Swapping the 5303A filter for the H-alpha filter is one part.

The main addition is a field stop between the end of the cone and the field lens. That produced the single biggest improvement in scattered light.

The 5303 filter is more sensitive to tilt that the H-alpha filter, so I made it closer to telecentric than the standard set up by moving the projection lens further back. I blackened a lot of surfaces that were a little reflective.

I also replaced the iris with a hard Lyot stop, which reflects less light. And put a Lyot spot near the stop.

The other main addition is picking the right objective lens. I am using a 50mm f/20 uncoated singlet lens made for high-powered lasers (low scratch and dig).

That's most of it. Then just iterating on the design and spacing, looking for sources of light that shouldn't be there and figuring out how to get rid of them (change spacing, shrink the field stop, etc.).

George


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Re: Corona from 24 September 2022

Post by Simon2940 »

Out of interest, how hard is it to make one of these coronagraphs? I would so love to try something like this out.


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Re: Corona from 24 September 2022

Post by george9 »

It took me about a year, and I had Klaus helping me out. I would have some issue, and he would recognize what was going wrong, or at least have some suggestions. Some basic optics knowledge helps.

Christian's Solar Astronomy book has general instructions how to make one and is the best current source I know of. Also reading work by or about Lyot, the inventor of this technique. But there is always something more to tweak.

i started with a Baader prominence viewer and converted that. After getting that to work, I had enough knowledge to build a better one: even better control of light scatter and more telecentric.

The 5303A filter is expensive. The double stack cost around $2000 and gets to about 1.2A, blocked 200nm to 2000nm, with assurance from the Andover that it also covers 2000-2500nm but they just don't measure it. And you'll need some way to keep that filter at a constant temperature, like a mica-based H-alpha filter; the 5303 is less sensitive though and a couple degrees swing is ok. Klaus originally used cheaper 5320A filters tilted to bring them on band.

I have very basic tools and I relied on piecing together parts from Amazon rather than making them. I have files, hack saw, hand drill, pliers, screwdrivers, vernier caliper, tin snips, etc. I would make jigs out of wood scraps to try to keep the parts square.

There is a lot of iteration and testing. I don't have easy access to the sky except out a window when the indoor and outdoor temperatures match. So that slowed me down. And as the coronagraph gets better, you need coronal skies to see if the instrument is performing, and they come rarely. Therefore, I set up a test bench indoors out of a bright LED, a lens, and a light trap set 30 feet away and used in the dark. That let me diagnose the coronagraph including looking up the tube without risking blindness.

George


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Re: Corona from 24 September 2022

Post by p_zetner »

Wow! This is extremely impressive!
I haven’t seen such clear imaging of the coronal loops before.
Congratulations.
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Re: Corona from 24 September 2022

Post by DeepSolar64 »

George,
Obviously these are more specialized than the simple 540nm green continuum filters we use for photosphere observing, and much more expensive. What spectral line is the 530nm filter(s) tuning onto?

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Re: Corona from 24 September 2022

Post by george9 »

530.3nm is Fe XIV, or very ionized iron, reflecting the super high temperatures of the corona. I just read that it was ascribed to a hypothetical element called coronium until 1939, when the iron origin was figured out.

George


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Re: Corona from 24 September 2022

Post by pedro »

very interesting thread


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Re: Corona from 24 September 2022

Post by MapleRidge »

Wow, very impressive work :bow

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Re: Corona from 24 September 2022

Post by DeepSolar64 »

george9 wrote: Fri Sep 30, 2022 8:47 pm 530.3nm is Fe XIV, or very ionized iron, reflecting the super high temperatures of the corona. I just read that it was ascribed to a hypothetical element called coronium until 1939, when the iron origin was figured out.

George
Interestingly one of the AIA telescopes onboard the SDO tunes also into an iron spectral line at a much shorter 17.1nm ( 171A ) wavelength to view the inner corona.

https://www.nasa.gov/content/goddard/sd ... -angstrom/

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Re: Corona from 24 September 2022

Post by marktownley »

Very interesting, thanks!


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Re: Corona from 24 September 2022

Post by george9 »

Yes exactly, James! That yellow image in my first post is SDO 171A. It's been really helpful that SDO images the corona constantly, so that when you look in the scope and think you see something, you can go right on your smartphone and check if the satellite shows anything bright in the same area. If it matches SDO and disappears when you lower the filter temperature, then you are pretty sure you are looking at the corona.

This was especially important with my old converted Baader prominence viewer, which had some aberrations due to a faulty field lens coating (my fault for using that lens) that led to some subtle glows in the field of view.

There is also STEREO (https://stereo.gsfc.nasa.gov/beacon/), which shows you what the Sun will be up to in two days by letting you peak around the side of the Sun based on the satellite location. It helps with planning whether to drive to the mountain in two days. It is the green false colored image, which is 195A and shows the corona well enough. They also have 171A, but they don't show the current image for some reason.

We are getting to the point where we don't need the corona to be as bright to see it. Our goal is to image the corona all the way around the Sun.

George


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

On a different note AIA1600 and CaK 3934a almost view the same layer of the Sun but with the former at a much shorter wavelength and views in the Carbon IV spectral line instead of Calcium. AIA304 images the Chromosphere but at a much shorter wavelength than Ha ( 6563a ) does. It images in the Helium II spectral line.

Anyway, back on topic. So I see a 540nm or broadband green filter is of no use in a coronagraph, right?

And to think during a solar eclipse the corona is much more easily and completely visible without a filter at all.

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Re: Corona from 24 September 2022

Post by george9 »

Right. I use 304A when I cannot tell which way my coronagraph is oriented and I don't want the Sun to drift out from under the cone. I get a shot in H-alpha, compare that to 304A to figure out my orientation, then when I shoot at 5303A, I can flip the 171A image around to the right spot without cheating (i.e., without forcing the 171A image to match my 5303 image).

Correct, 540nm won't be helpful.

To all, please correct the following as needed:

The corona looks white during an eclipse because you are seeing the K-corona near the Sun or F-corona further away, and they both have a broad spectrum. The E-corona or emission corona is dimmer than the K-corona but is limited to narrow wavelengths. For the coronagraph, there is still too much scattered light and while the K-corona may be brighter, the E-corona's energy is confined to those narrow bands and with our 1.2A filter, we can get a much better signal-to-noise ratio at 5303A than the K-corona. That is, a 1.2A filter eliminates all but 1.2/3000 of the background scatter yet much of the E-corona's energy is still passed by the filter in that strong band.

Klaus has been working on the K-corona and at least exploiting polarization, but no luck yet.

George


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

George,
What would we do without those valuable SDO images :-)

The MLSO K-Cor Coronagraph uses polarization for it's magnificent corona images. It's among the best coronagraphs on Earth!

20221002_172801_kcor_l2_nrgf_cropped.gif
20221002_172801_kcor_l2_nrgf_cropped.gif (170.16 KiB) Viewed 1095 times
James


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Re: Corona from 24 September 2022

Post by Radon86 »

george9 wrote: Wed Sep 28, 2022 10:46 am Thanks very much. I will point out that I learned how to do it from Klaus160. And Christian's book was helpful with its easy-to-use formulas for the optical design. (And we all owe Lyot.) The hard part was debugging all the stray light in the system.

George
Where is this formula for the optical design.
I had difficulty finding this in the Solar Astronomy book.

What telescope are you using to apply the coronagraph ?

Thanks

Magnus


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Re: Corona from 24 September 2022

Post by Radon86 »

Is the corona harder to image than the Sun in H-alpha ?
A guide to this imaging sub speciality would be very helpful I think.

Are other solar imagers also interested ?

Magnus


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Re: Corona from 24 September 2022

Post by george9 »

Hi. I am talking about Appendix 2 on page 234 of the Solar Astronomy book English version. I know there were additions, so not sure if the French version has Appendix 2. I know an update to that is planned.

I am using a Celestron FirstScope 80mm (910mm f.l.). I removed the objective and built a cell on the end of the dew cap because I am using a 50mm f/20 (1000mm f.l.) lens. It is an uncoated singlet with 10/5 scratch-dig (highly polished). I also removed the baffles from the OTA because I don't want light from the cone reflecting back down the tube.

The corona is way harder than H-alpha because it is 100 times dimmer.

George


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

Yes, the corona should be much dimmer than the chromosphere and therefore much more difficult.


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Re: Corona from 24 September 2022

Post by Montana »

This is truly remarkable and the best you have displayed here :bow :bow :bow and thank you for the information, if only I was brainy enough to do this, had the spare cash and had a high mountain nearby ;)

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Re: Corona from 24 September 2022

Post by DeepSolar64 »

Alexandra, You do have a starting point. A Baader Prominence viewer! Draft Mr.Townley to help you convert it into a true Coronagraph! He's an expert modder and tinkerer!


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Re: Corona from 24 September 2022

Post by george9 »

Alexandra, as James points out, you have a great start. Adding a field stop should feasible. You can iterate on the rest as needed.

The big challenge is the cost and temperature regulation of the 5303A filter.

But there are other fun things you can do with a just a little tinkering. For example, image prominences at other wavelengths, like H-beta, H-gamma, helium D3, other helium. Even image prominences with no filter (broad band for true color). The latter requires clear skies and improved scatter of the Baader prominence viewer, similar to coronal viewing.

I have seen the corona at sea level, just about 20 yards from the sea, in fact. It was a very clear fall day. So you may not need a mountain. But mountain does help a lot. The image in this post was actually not my usual 3200-foot mountain but a 2300-foot (700 meter) star party field.

George


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Re: Corona from 24 September 2022

Post by DeepSolar64 »

The true magenta-pink combined color of H-Alpha and H-Beta prominences is absolutely beautiful!!


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