Selecting Narrowband Solar Observing Equipment
Posted 13 September 2011 - 02:53 PM
By John Crilly.
Posted 13 September 2011 - 04:23 PM
"When we speak of white light solar observing, we mean that we are looking at the full spectrum. We may be using color filters, but we aren't completely blocking any wavelengths. We can see the photosphere of the sun. We may see sunspots and the activity surrounding them. We may see the “rice grain” effect of the boiling outer surface. We may even detect filaments."
Nope, solar filaments are *not* visible in white light. They require very narrow passband H-alpha filter systems (FWHM of less than one angstrom) in order to be seen. The only thing one might see in white light would be the fine fibril structure in the penumbrae of some sunspots. If you want to see filaments, you have to have either a spectrohelioscope or an etalon-based ultra narrow-band H-alpha filtering system. Thankfully, these H-alpha solar filters/telescopes are somewhat more affordable than they used to be. Clear skies to you.
Posted 14 September 2011 - 04:32 PM
Posted 14 September 2011 - 06:32 PM
I remember having seen "brush strokes" with a mylar filter, basically doing "white light" solar observing. As far as I know those are actually filaments. Please correct me if I am wrong.
I'm not certain exactly what you saw, but it was definitely not a solar filament. Filaments are large clouds of magnetically-confined gas located above the photosphere of the sun. They absorb light over a *very* narrow range of wavelength (less than 1.5 angstroms) and are completely wiped out by the brilliant broad-band emission of the underlying photosphere. They cannot be seen except in ultra narrow-band H-alpha filtering systems or with a spectroheloscope. It is possible you were seeing a contrast effect caused by intense white-light faculae which can appear somewhat filamentary in nature but are not filaments. Faculae is seen near the solar limb as small brighter patches in or quite near active regions. These patches are somewhat related to the brighter H-alpha patches known as "plage" but again are not quite the same thing, since plage and faculae do not necessarily appear in identical locations. In any case, filaments are not visible in standard white-light solar filters. Clear skies to you.
Posted 15 September 2011 - 11:15 PM
Informative article. Thanks for submitting it.
I've been bitten by the H-Alpha bug, I think.