| BYoesle |
| (Pooh-Bah) |
| 04/17/08 01:53 AM |
|
Re: Using a Nightime H-Alpha filter for Solar view
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Thanks David, you are of course correct in many details.
Given the frequency of those new to solar observation and asking this same question of using nebula/white light filters to view the sun, I was trying to keep the concepts simplified, as the details may tend to bewilder a person new to solar filters, and unfamiliar with solar physics and spectroscopy.
I might disagree about the visibility of the Ca H & K lines, as these are in a part of the spectrum the eye is even less sensitive too than the H alpha line, as you note.
Quote:
It might be a little more general to say that the reason broader "nebula" H-alpha filters won't show the chromospheric detail is that they are letting in a little too much off-band light from the photosphere. That light is basically "drowning out" the weaker chromosphere... With a regular white-light solar filter, you would, of course, dim the chromospheric emission, but the H-alpha filter would still be letting in too much light from wavelengths well away from the H-alpha centerline, and that is the crux of the problem.
The off-band contamination of a broad-band H alpha nebula filter used with a white light filter is irrelevant and only adds insult to injury: chromospheric details and prominences will be invisible with a white light filter because they are rendered 100,000 to 1,000,000 times fainter than they otherwise would be. That's why during the totality phase of a solar eclipse you do not see anything through a telescope equiped with a white light filter, where there is no side band contamination whatsoever.
This is easy to verify, since a narrow-band H alpha filter passes ~ 95% + of the H alpha emission -- just place a white light filter in front of your PST or other H alpha solar filtered telescope -- there will be no image to observe, even without photosphereic side band contamination.