Prominences in different wavelengths and the solar corona

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Prominences in different wavelengths and the solar corona

Post by hk160 » Sun Nov 22, 2020 2:41 pm

I have been a silent reader here for a while and I saw may interesting topics, some pertaining to what I will show below. Usually, I lack the drive post (much), but I think/hope I have something interesting to share, so I made the effort this time.

I also hope it is OK per forum rules to just post a link to the original posts in another forum, since uploading pictures and re-post seems like such a drag …

However, in short, I have been building coronagraphs/prominence scopes for many years. The 2017 eclipse (my first total one!) re-kindled my interest and led me to build the next generation of instruments.

I was able to observe (and image) prominences in other wavelengths than H-alpha as can be seen here

https://www.cloudynights.com/topic/6425 ... velengths/

and just recently (i.e. this week), I was able to see and image the corona itself

https://www.cloudynights.com/topic/7403 ... yesterday/


I have not found references of other observations (by amateurs) for either of these, therefore I would like to share in case anyone else is interested in building a similar instrument.

Also, please let me know if you have any questions – I am happy share more details of the setup or the observations.



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Re: Prominences in different wavelengths and the solar corona

Post by AndiesHandyHandies » Sun Nov 22, 2020 4:18 pm

Hi

Thanks for posting.

I have had a little experience using a prominence scope at Puimichel in France.

Cheers. Andrew.



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Re: Prominences in different wavelengths and the solar corona

Post by Starry Jack » Sun Nov 22, 2020 4:34 pm

I just scanned the photos but even just doing that I am intrigued. Certainly a worthy topic here!

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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Tue Nov 24, 2020 1:53 am

Thank you for the kind comments!

I went again today, but that will be it for a while now. I may post more later, but here is an image I took today

Image


and its level adjusted version

Image

I also measured the stray light today, and sky+Coronagraph together were a little under 20 millionths of disc brightness, which is pretty good considering that the conditions were not as good as on Friday.


P.S.: not sure if the images work or how to upload them better. They can also be found as the last post in the thread I linked above.



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Re: Prominences in different wavelengths and the solar corona

Post by DeepSolar64 » Tue Nov 24, 2020 7:19 am

I find it amazing that you were able to detect the solar corona from as low as Mt. Mitchell at 6684Ft above sea level. I would have expected a drier site and one at least at 10.000 feet asl. I live in western North Carolina and have been to Mt. Mitchell quite a few times and have hiked the Black Mountains as well. The hike from Mitchell to Mt Celo is awesome!! Mitchell is about a 30 min drive from my home.


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Re: Prominences in different wavelengths and the solar corona

Post by Carbon60 » Tue Nov 24, 2020 7:39 am

Impressive. Thank you.

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Re: Prominences in different wavelengths and the solar corona

Post by Montana » Tue Nov 24, 2020 11:48 am

Wow!! :bow :hamster:

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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Wed Nov 25, 2020 1:39 am

Thanks for all the comments!

> I find it amazing that you were able to detect the solar corona from as low as Mt. Mitchell at 6684Ft above sea level. I would have expected a drier site and > one at least at 10.000 feet asl.

I was somewhat surprised as well, especially because of the vegetation on the summit. It is not elevation alone though - Wendelstein Observatory is only at 6030 ft, but used to be the primary German site to observe the Corona (http://www.wendelstein-observatorium.de ... st_en.html , scroll to the coronograph part as well)
You probably pay for the low elevation by sky quality (as I said, I have much better skies) and by how many coronal days you have per year.

> I live in western North Carolina and have been to Mt. Mitchell quite a few times and have hiked the Black Mountains as well. The hike from Mitchell to Mt > Celo is awesome!! Mitchell is about a 30 min drive from my home.

The only hike I have done so far is the Balsam trail which is that tiny 15 min loop at the peak :)

Since you are so close, you are more than welcome to stop by the next time observe - I will drop you a note if you are interested. Also, if you are near Hickory, you can stop by and I can show you the instrument and the prominence if it is sunny. However, I only live there part time, and am now back in NY for the next few weeks.



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Re: Prominences in different wavelengths and the solar corona

Post by DeepSolar64 » Wed Nov 25, 2020 6:00 am

hk160,
Sure, I would love to meet up with you sometime. The weekends would be best since I work during the week. Just let me know beforehand. I would love to be there with you during a corona viewing session!

The only time I have seen the corona was during the 2017 total solar eclipse. It's something I won't soon forget. Of course your instrument will only see vestiges of the innermost corona unlike the extensive view during a total solar eclipse. But still, that's a great accomplishment.

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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Wed Nov 25, 2020 5:42 pm

I will let you know. However, I will not be back until next year though (yes, "Corona" is also limiting my travel plans ...), and then hopefully the Parkway and the Mt. Mitchell itself will still be open. The look-out at the top where Hwy 80 meets the Parkway might be good enough, but that is only 3,400ft high ...

> The only time I have seen the corona was during the 2017 total solar eclipse. It's something I won't soon forget. Of course your instrument will only see > vestiges of the innermost corona unlike the extensive view during a total solar eclipse.

Yes, probably good to set the expectations and point out that this looks nothing like a solar eclipse. You do see the black disc surrounded by a darker green (in good conditions), and the regions showing up in brighter green. The pictures indicate that the brightest parts of the corona are 2-3x as bright as the background. You do see some structure though, e.g. the rays as shown in the last pictures I took. Visually, prominences are much more impressive, but then again it is pretty cool to know that you are probably the only person that day who is seeing the solar corona with their own eyes.

> Of course your instrument will only see vestiges of the innermost corona unlike the extensive view during a total solar eclipse.

Such is the lot of ground based observation ... the while a Coronagraph can get below 1 millionth, the earth atmosphere seldom gets better that 10 millionths (https://atst.nso.edu/sites/atst.nso.edu ... m_inst.pdf), and the inner corona is in the range of 1-3 millionths.
Therefore the need to go to emission lines or polarization (K-Corona). The other problem is the the emission line corona falls of very quickly with distance.



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Re: Prominences in different wavelengths and the solar corona

Post by DeepSolar64 » Wed Nov 25, 2020 6:27 pm

Here is where I usually go for corona data, other than the SDO.

https://www2.hao.ucar.edu/mlso/mlso-home-page


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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Thu Nov 26, 2020 12:59 am

Yes, I use that one for reference as well. The K-Corona seems to look quite a bit different from the 5303 though, so I only use it for an overview/activity indicator.

However, there is an interesting addition: If you go to the end of the original post

https://www.cloudynights.com/topic/7403 ... yesterday/

someone took the SOH EUV 171 and oriented it as seen in my scope - and the details seem to match up quite nicely. In the future, I will refer to that as well when planning my observation trip. One obvious advantage is the cadence of the image - and that there is no clouds in space :)



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Re: Prominences in different wavelengths and the solar corona

Post by DeepSolar64 » Thu Nov 26, 2020 3:35 am

Would a polarizer help in seeing the corona in an amateur setup? I have also been trying to find that link to the green corona images but have not succeeded yet.


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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Fri Nov 27, 2020 1:27 pm

> Would a polarizer help in seeing the corona in an amateur setup?

Good question. It may enhance the features if the polarization is lined up in that particular direction, but the real benefit comes from subtracting aligned and perpendicular pictures. That means that image processing is needed to get the full benefit of this method, and it is probably not that suitable for visual observation.

I might try it eventually though, probably combining it with an orange or red filter. I will also need to read up on how this is done - I may be missing something.



> I have also been trying to find that link to the green corona images but have not succeeded yet.

Yes that link is down for some reason. However, now the Russian website is up again

http://en.solarstation.ru/sun-service/corona

However that only gives intensity in certain directions and is not very frequently updated.



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Re: Prominences in different wavelengths and the solar corona

Post by christian viladrich » Wed Dec 02, 2020 11:01 am

I've nearly missed this post ...
This is absolutely amazing !! I don't know of any amateur observation of the corona. This is a first !
Because of the solar minimum, the green line corona is not very bright. Its brightness will increase with the increasing activity of the Sun.
Polarization is used for observation of the K-corona. Indeed the K-corona (= plasma corona) is polarized, while the F-corona (dust corona) is not.


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Re: Prominences in different wavelengths and the solar corona

Post by highfnum » Wed Dec 02, 2020 12:06 pm

THIS IS REAL INTERESTING
i built an SPV i wonder if it could be modified for this
this was my spv prom shot
i never thought it could be used or any version be used for corona
spv9.jpg
spv9.jpg (45.27 KiB) Viewed 392 times



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Re: Prominences in different wavelengths and the solar corona

Post by DeepSolar64 » Wed Dec 02, 2020 4:00 pm

Just because something is difficult doesn’t always mean it’s impossible. Amateur astronomers have always been an ingenious bunch and have succeeded in many areas professionals would have thought impossible. Why should viewing/imaging the solar corona be any different? It’s simply a challenge to be met.

You can bet. Someone’s gonna do it!!!


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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Wed Dec 02, 2020 6:59 pm

Thank you for the responses!

I will reply here and on the other site, depending where the pictures are – sorry for the split screen action …

> i built an SPV i wonder if it could be modified for this
> this was my spv prom shot
> i never thought it could be used or any version be used for corona

I have never really bought into the distinction between coronagraph and prominence telescope. Every coronagraph will show the prominences and the basic design is the same anyway.

However, it is indeed more difficult to build a coronagraph since the requirements for stray light suppression are so much higher. This starts with the objective being a simple lens, continues with blackening all the parts extremely thoroughly (especially around the cone area and the Lyot stop), and ends at having the correct optical design (e.g. a high f-number) to allow for the correct use of a narrowband filter.

But in principle, there is no difference between the instruments. If you look through the other thread, there are some comments on how much fainter the corona is and how you can test whether your prominence scope would be capable of showing it.



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Re: Prominences in different wavelengths and the solar corona

Post by DeepSolar64 » Wed Dec 02, 2020 7:26 pm

I think the Baader Coronagraph is more set up as a prominence viewer. It has Ha filters for one which a true coronagraph shouldn't need. I wonder if the Ha filters would actually reduce the chance of seeing the corona? Alexandra has one and could give comments.

One needs an excellent instrument, high altitudes and dry air to have a chance anyway. And hk160 you have beaten the odds where many have failed. But most of us feel it's impossible and fail to try.


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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Wed Dec 02, 2020 8:01 pm

> I think the Baader Coronagraph is more set up as a prominence viewer. It has Ha filters for one which a true coronagraph shouldn't need. I wonder if the Ha filters would actually reduce the chance of seeing the corona? Alexandra has one and could give comments.

Well, I think I can comment here since I own one as well…

First off, yes, you do need to remove the h-alpha filter, otherwise you will not see the corona.
There are at least two versions of the Baader viewer that I know of: one has a fixed 30 mm 10A filter, the other one (later unit) has just a provision for standard 1 ¼ inch filters such as the 1,5A filter which Baader sold with the unit.
In both cases the filter can be removed, even though in the first case it is a little bit more effort. I have done this for the unit that I own in order to use my own filters instead of the one that was in there which had already deteriorated.
Still, while I think that the Baader unit is a good and solid performer, there are some things that may limit its use for corona viewing such as the optical train not being telecentric.

> One needs an excellent instrument, high altitudes and dry air to have a chance anyway. But most of us feel it's impossible and fail to try.

True, especially the last sentence.
As you point out, this is not trivial and requires quite an investment such as the filters, but since you feel it is impossible, you don’t even try. This, and life happening in general, delayed me for about 20 years :)
Also, it should be noted, that (cheaply) available technology is crucial: getting a suitable lens off-the-shelf for one, but then also having extremely narrow band filters available off-the-shelf is well. Without these items it would not be possible to be successful, and those were certainly not easily available 20 years ago.



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Re: Prominences in different wavelengths and the solar corona

Post by DeepSolar64 » Wed Dec 02, 2020 8:30 pm

Does Baader still make their coronagraph?


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Re: Prominences in different wavelengths and the solar corona

Post by hk160 » Thu Dec 03, 2020 12:08 am

No, unfortunately not.

I think Baader stopped selling them over 10 years ago – I suspect that the PST especially was its demise: a PST is much easier to operate, requires a much smaller mount and costs less than half as much - and you can see the solar disk.

I own a PST myself and I really do like it – however, it will never show prominences as nicely as a dedicated prominence viewer. For comparison: I own the PST which is 40 mm, built a coronagraph which is also 40 mm and I have also built a smaller version coronagraph with 20 mm aperture. The PST and the 20 mm coronagraph are very comparable when it comes to prominences. The PST, obviously, has a higher resolution, but the coronagraph has a much better contrast if the sky permits it. In addition, because you have more light because of the higher filter transmission, you can also magnify higher relative to its aperture.
There is simply no comparison between the PST and 40 mm - that one wins hands-down.


You can still buy a prominence viewer though: there is this one from Wolfgang Lille himself who is also the constructor of the original Baader unit. The new units are different though:

http://sonnenfernrohr.de.w0199a68.kasse ... nansaetze/

And then there’s Oliver Smie who also sells prominence viewers (or at least used to as I just see now):

https://beloptik.de/en/solar-coronagrap ... ce-viewer/

I have no experience with the above units, obviously. If you’re really interested, I suspect your best bet is to put out a ‘wanted ad’. That is what I did earlier this year and was able to buy a unit for about $300.



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Re: Prominences in different wavelengths and the solar corona

Post by Montana » Thu Dec 03, 2020 12:20 pm

Thanks for all the info, very interesting indeed. I did wonder about the Baader Coronagraph I had, so thank you for the explanation. I must get it out more ;)

Alexandra



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