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Space Forum / Amateur Astronomy / June 2006Ca-K filters. Are they partially in the UV spectrum?
Hi Everyone, A friend of mine said recently that he looked at the Sun through what he thought was a Ca-K (Calcium-Potassium) filter, and he didn't see much. He thought it was because his eyes weren't sensitive enough to get much from this filter. I thought that the dominant line that such a filter passes is at the high end of the spectrum, but not into the UV much. Is it? What do you gain by looking in this band rather than the H-alpha band? Thanks in advance ! Sincerely, --- Dave Nakamoto ======================================== Miller's Daughter --- There, I was visited by a bizarre, strange imp of a man. Sam Shovel --- Pee Wee Herman? Miller's Daughter --- Not THAT strange. >Hi Everyone, > [quoted text clipped - 5 lines] >I thought that the dominant line that such a filter passes is at the >high end of the spectrum, but not into the UV much. Is it? I'm sure the filter was selecting the calcium II K line (no potassium involved), at 393 nm, which isn't UV. It is, however, a very deep blue or violet (different people see it differently), which is a color range where your cone density is very low, and therefore your acuity is also low. It is a poor color for working in visually, and many people will have problems there. Far better is to use this filter with a camera, and view the image as gray scale. >What do you gain by looking in this band rather than the H-alpha band? CaK absorption is very sensitive to magnetic fields. In the presence of a strong field, absorption is reduced and you get a brighter image. With Ha, you are looking at the emission of neutral hydrogen, which is the primary constituent of the outer layers of the Sun. So basically, these two bands reveal very different structures and physical processes. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com >> Hi Everyone, >> [quoted text clipped - 12 lines] > have problems there. Far better is to use this filter with a camera, and > view the image as gray scale. That's what I suggested to my friend. The added advantage of using a web camera is the ability to stack and sharpen the images later. Thanks for clarifying the meaning of the K in Ca-K Chris ! >> What do you gain by looking in this band rather than the H-alpha band? > [quoted text clipped - 3 lines] > primary constituent of the outer layers of the Sun. So basically, these > two bands reveal very different structures and physical processes. Gotcha ! So Ca-K shows you distribution of magnetic events on the surface of the Sun. Interesting, particularly since where there's magnetic fields, there's usually activity on the Solar surface. Thanks again for the answers Chris ! Sincerely, --- Dave Nakamoto ======================================== Miller's Daughter --- There, I was visited by a bizarre, strange imp of a man. Sam Shovel --- Pee Wee Herman? Miller's Daughter --- Not THAT strange. I believe the CaK is lower into the "surface" if a plasma ball has a surface. It's a bit lower in the photosphere from what I understand than the white light or Ha filters show. >>> Hi Everyone, >>> [quoted text clipped - 38 lines] > Sam Shovel --- Pee Wee Herman? > Miller's Daughter --- Not THAT strange. No, the Ca II K and H lines are singly ionized emissions in the lower chromasphere approximately 2-3K kilometers above the photoshpere. Clear skies, Bill > I believe the CaK is lower into the "surface" if a plasma ball has a > surface. It's a bit lower in the photosphere from what I understand than the > white light or Ha filters show. No, the Ca II K and H lines are singly ionized emissions in the lower chromasphere approximately 2-3K kilometers above the photoshpere. Clear skies, Bill > I believe the CaK is lower into the "surface" if a plasma ball has a > surface. It's a bit lower in the photosphere from what I understand than the > white light or Ha filters show. lattosimbaste@gmail.com Wrote: > No, the Ca II K and H lines are singly ionized emissions in the lowe > chromasphere approximately 2-3K kilometers above the photoshpere. Clea > skies, Bill So why do they actually appear 'dark' in the solar spectrum if the are, as you quote, in 'emission'? Puzzled! Nyteca -- nytecam Nytecam posted: > lattosimbaste@gmail.com Wrote: > [quoted text clipped - 4 lines] > So why do they actually appear 'dark' in the solar spectrum if they > are, as you quote, in 'emission'? Puzzled! The lines are only relatively dark when compared with adjacent contiuum areas of the spectrum. They do not represent a total absense of emission at that wavelength. Near the center of the lines, there is some emission from Calcium present, so with a filter which is narrow enough to exclude the brilliant emission from areas of the spectrum adjacent to the Calcium lines, that weaker "in-line" emission can be seen. Clear skies to you.  SignatureDavid W. Knisely KA0CZC@navix.net Prairie Astronomy Club: http://www.prairieastronomyclub.org Hyde Memorial Observatory: http://www.hydeobservatory.info/ ********************************************** * Attend the 13th Annual NEBRASKA STAR PARTY * * July 23-28, 2006, Merritt Reservoir * * http://www.NebraskaStarParty.org * ********************************************** > Nytecam posted: > [quoted text clipped - 15 lines] > seen. Clear skies to you. > -- are you sure? ever done it? > David W. Knisely KA0CZC@navix.net > Prairie Astronomy Club: http://www.prairieastronomyclub.org [quoted text clipped - 5 lines] > * http://www.NebraskaStarParty.org * > ********************************************** > are you sure? ever done it? *Plonk* Sam Wormley Wrote: > are you sure? ever done it? > *Plonk* Hi Sam - is that a considered reply?;-) I've always assumed that H-alpha @ 656nm and CII @ 393nm viewed on th solar disk were via dark absorption lines and not bright emissio lines. OK there are variation in relative brightness within th absorption line otherwise the various phenomena like filament [dark and plage [bright] within the absorption line would remain invisibl but that doesn't indicate emission. I reserve that for filaments see clear of the limb as prominences. regards - Nytecam www.astroman.fsnet.co.u -- nytecam > I've always assumed that H-alpha @ 656nm and CII @ 393nm viewed on the > solar disk were via dark absorption lines and not bright emission [quoted text clipped - 3 lines] > but that doesn't indicate emission. I reserve that for filaments seen > clear of the limb as prominences. Well, when you look at the spectrum of the sun with a spectroscope, the H-alpha and Ca II K lines do look somewhat dark, as the overall effect is absorption at those wavelengths. However, a detailed light intensity measurement at very high dispersion will show that the brightness profile of the spectral lines never goes completely to zero at their central wavelengths. There is some emission in the middle of the line from both excited Calcium and Hydrogen, so with a narrow enough filter passband, the rest of the continuum gets excluded and you see the chromosphere as bright from that weak emission. Some features on the sun do absorb light in the H-alpha line but they still radiate it as well. Filaments on the solar disk look dark because they absorb light from just below the filament but then re-radiate it in all directions. The net flux that we see is thus lower than it is in adjacent disk regions, so the filaments look somewhat darker than the surrounding area. However, once the sun rotates and a filament appears up on the limb against the darkness of space, you then see that re-radiated energy and the "filament" now appears as a brighter emission feature. The filament is then re-named a prominence, even though physically, they are basically the same thing. Clear skies to you. SignatureDavid W. Knisely KA0CZC@navix.net Prairie Astronomy Club: http://www.prairieastronomyclub.org Hyde Memorial Observatory: http://www.hydeobservatory.info/ ********************************************** * Attend the 13th Annual NEBRASKA STAR PARTY * * July 23-28, 2006, Merritt Reservoir * * http://www.NebraskaStarParty.org * ********************************************** David Knisely Wrote: > I've always assumed that H-alpha @ 656nm and CII @ 393nm viewed o > the [quoted text clipped - 33 lines] > -- > David W. Knisely Thanks David - I can see we largely agree when the highest spectra resolution is assumed as I can testify from *within* the McMat [Pierce] Solar Telescope on Kitt Peak during a visit in 1980 hosted b Dr Pierce! With amateur spectrographs, like mine, these subtl emission features may not be evident. regards Nytecam http://www.astroman.fsnet.co.uk/newspec.ht -- nytecam nytecam posted: > Thanks David - I can see we largely agree when the highest spectral > resolution is assumed as I can testify from *within* the McMath > [Pierce] Solar Telescope on Kitt Peak during a visit in 1980 hosted by > Dr Pierce! With amateur spectrographs, like mine, these subtle > emission features may not be evident. One thing which was done before narrow-band sub-angstrom filters were produced commercially was to for amateurs to use a visual spectroscope tuned to the H-alpha line and, with an occulting disk in place to cover the bright solar disk, widen the jaws of the spectroscope's slit and then scan around the solar limb to pick up the prominences. A few also passed a spectroscope slit over active regions where bright plage or a solar flare would often make the H-alpha line appear bright rather than dark, although I would not recommend this. Eventually, a number of amateurs constructed their own specoheloscopes to watch the action over the whole solar disk. Clear skies to you. SignatureDavid W. Knisely KA0CZC@navix.net Prairie Astronomy Club: http://www.prairieastronomyclub.org Hyde Memorial Observatory: http://www.hydeobservatory.info/ ********************************************** * Attend the 13th Annual NEBRASKA STAR PARTY * * July 23-28, 2006, Merritt Reservoir * * http://www.NebraskaStarParty.org * ********************************************** David Knisely Wrote: > nytecam posted: > [quoted text clipped - 3 lines] > snip -- > David W. Knisely Done that David and got the T-shirts lik http://home.freeuk.com/m.gavin/ebert.htm http://www.astroman.fsnet.co.uk/needle1.htm Nyteca -- nytecam |
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