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Comet Filters


Mark in Macc

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I've not used one Mark, but they seem very specific to comets with ionised tails. From looking at the specs I would expect them to be better than than an OIII because they are tuned for two additional lines at 511 and 514 nm which may get cut off by an OIII.

Was there a particular comet you had in mind? Jacques seems to be dusty rather than having an ionised tail so I suspect wouldn't be a suitable target.

Would have been perfect for something like Hale-Bopp I expect

Stu

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Ever notice that comet pix often appear somewhat greenish?  Those are the Cyanogen lines at 511 and 514nm.

Add those to the 501nm O-III and comets with ion tails will be strongly enhanced.

That the filters don't work well on all comets is no different than an O-III filter not working well on all nebulae.

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Ever notice that comet pix often appear somewhat greenish?  Those are the Cyanogen lines at 511 and 514nm.

Add those to the 501nm O-III and comets with ion tails will be strongly enhanced.

That the filters don't work well on all comets is no different than an O-III filter not working well on all nebulae.

Normally said to be the C-C emission bands isn't it? The prominent C-N band is shorter wavelength I think.

Chris

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  • 2 years later...

The 511 and 514nm peaks in comet spectra are due to the fluorescense of neutral diatomic carbon molecules (first observed by Swan in the 19th century in Bunsen burner flames - now called Swan bands in spectra). The energy source for this is in comets UV light from the sun. CN radicals have a strong emission band right on the UV/violet border. The principle source of emission light from ion tails is from ionised carbon monoxide which is strongly blue. Dust tails just reflect sun light (so can be seen in any visible light filter though much dimmer than without a filter).

The upshot of this is Comet aka Swan band filters are principally for increasing the contrast of the coma of non dusty comets. To enhance the blue ion tail they would have have rather broad pass band. This filter will NOT pass any light due to CN whose light is on the edge of visibility to human eyes (very deep violet). BTW "CN" is not cyanogen - cyanogen is a 4 atom molecule with the formula (CN)2 the dimer of CN. CN is the nitrile (aka cyano) radical.

The is a huge amount of misinformation about the sources of light emitted by comets. You may have noticed that various Nasa related websites such as Spaceweather no longer trot out the myth that the green light of a comet coma is due to cyanogen. That myth goes back to the scaremongering that went on in 1910 when the Earth passed through Halleys comet tail and quacks sold "comet pills" to save you from gas poisoning (!). Somehow during the early days of the internet the cyanogen myth got ingrained into explaining comet coma colours.

Tony (PhD chemistry :))

PS this lengthy thread over on Cloudynights has the uncovering of the source cyanogen error in the primary astronomy literature (late Victorian era) - you need a bit of stamina to get to the big reveal - https://www.cloudynights.com/topic/406505-green-in-comets-is-not-cn-cyanogen/

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On 8/28/2014 at 18:25, Don Pensack said:

Ever notice that comet pix often appear somewhat greenish?  Those are the Cyanogen lines at 511 and 514nm.

Add those to the 501nm O-III and comets with ion tails will be strongly enhanced.

That the filters don't work well on all comets is no different than an O-III filter not working well on all nebulae.

Thanks, Don, for sparing me from explaining the 511nm & 514nm bands as being Cyanogen!

Will the SWAN-Filter (Comet-Filter from Lumicon) enhance a comet's tail? Each comet is different, and there's only one-way to see if the SWAN helps - try it! Such is ½ the fun! And please post your findings. At present, there's no definitive list.

Cyanogen = Cosmic-Cyanide,

Dave

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