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Lines giving useful (& beautiful) data in visible spectrum are well known - H-b, O-III, H-a, S-II. Unfortunately light pollution is strongest in visible light.

Are there similar relatively bright lines in NIR 700-1500nm, especially 700-1000nm spectral range where one could image deep sky objects with proper gear?

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  • $\begingroup$ Narrowband imaging exploits the fact that nebulae emmit light at wavelengths which typically don't appear in light pollution. Hopefully, efficient ligting wouldn't emmet much IR, so any IR wavelengths would be better than visible wavelengths. But, unless nebulae also emmit at those wavelengths, it won't help. $\endgroup$ Apr 11, 2023 at 15:41
  • $\begingroup$ Note that by "other gear" you are going to need a back-illuminated CCD for wavelengths beyond 900 nm and maybe an entirely different sort of detector for much beyond 1000 nm. $\endgroup$
    – ProfRob
    Apr 11, 2023 at 22:40
  • $\begingroup$ @ProfRob Fortunately, up to 1000nm that's exactly what I have at hand - BSI sensor on IMX492, and looking where to utilize it :-) $\endgroup$ Apr 12, 2023 at 1:06

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Yes, there are some obvious nebular emission lines in this range - the whole of the Paschen series (transitions in hydrogen atoms to the $n=3$ level) lie between Paschen alpha at 1875 nm to the Paschen limit at 820 nm. The following is a color-composite of the Orion nebula where the "red" channel is formed from an image using the Paschen 9 line at 923 nm (green is Balmer alpha at 656 nm and blue if Balmer beta at 486 nm).

MUSE VLT Orion Nebula

Another example would be the neutral Helium 1083 nm line that is often used to image the hot chromosphere of the Sun. For example, this image

Helium image

Note that the Earth's atmosphere is effectively opaque between 1350-1500 nm.

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    $\begingroup$ Thanks for very interesting image at 932nm! I afraid this 1083nm image is using some freaking narrow bandwidth of <1nm... $\endgroup$ Apr 12, 2023 at 3:33
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The main problem with NIR is that the atmosphere quickly becomes opaque for various bands inside the range due to the absorption bands of water vapour. E.g. see a lecture document on spectral transmittans of the atmosphere here.

This said, there might be some interesting lines in the parts where the atmosphere is transparent in the NIR. For amateur observers mostly lines of planetary nebulae and molecular clouds might be interesting. Rudy et al lists some. I found on some amateur site an overview over filters used by some for NIR observations.

From a practical POV, the availability and price of the filters might be an actual concern for amateur observers for narrow-band filters of more-or-less obscure wavelengths.

You can also look through the complete database of lines - but that might be slight overkill.

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    $\begingroup$ Article by "Rudy et al" is extremely helpful, thanks alot! Is there a chance you know few more articles like this, probably about other DSO? Or keywords you used to find it? $\endgroup$ Apr 11, 2023 at 17:58
  • $\begingroup$ A search for "nir lines important nebula" turned up Rudy et al, or maybe it was "astronomy nir lines nebula". Both give some further paper which might be interesting to you. $\endgroup$ Apr 11, 2023 at 21:18

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