Hello folks.
So I happened to be imaging M81 & M82 with a dual band OSC with 5nm Ha/Oiii filter on Fri 10 May when the aurora arrived. Here's the image - is this reddish/purplish "nebulosity" the aurora? It's not there in previous 8hrs of data on the same target (see other image in my collection), and aurora does involve excitation of O2 molecules...
https://www.astrobin.com/w89cr3/
Thank you,
Vin
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Hello folks.
So I happened to be imaging M81 & M82 with a dual band OSC with 5nm Ha/Oiii filter on Fri 10 May when the aurora arrived. Here's the image - is this reddish/purplish "nebulosity" the aurora? It's not there in previous 8hrs of data on the same target (see other image in my collection), and aurora does involve excitation of O2 molecules...
https://www.astrobin.com/w89cr3/
Thank you,
Vin
I think the aurora did have an effect on the image, but I can't say for sure if it's only because of the aurora
could be also that you did a combination of a little too much stretching and denoising
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The red of aurora comes from OI at 6300 Ang. So if you see faint red light in your OSC image under an Ha/OIII filter, it's Ha, not aurora. And of course, it can be continuum light at the Ha wavelength, not necessarily Ha itself, and light pollution can do this. But anyway it's not aurora.
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Wei-Hao Wang:
The red of aurora comes from OI at 6300 Ang. So if you see faint red light in your OSC image under an Ha/OIII filter, it's Ha, not aurora. And of course, it can be continuum light at the Ha wavelength, not necessarily Ha itself, and light pollution can do this. But anyway it's not aurora.
Correct me if I'm wrong. As far as I know, there are many more emission lines in Aurora and some are near Ha-line. I'd guess some might fall into the filter's band., but I'm just speculating.
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Kay Ogetay:
Correct me if I'm wrong. As far as I know, there are many more emission lines in Aurora and some are near Ha-line. I'd guess some might fall into the filter's band., but I'm just speculating.
I thought so too
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Kay Ogetay:
Wei-Hao Wang:
The red of aurora comes from OI at 6300 Ang. So if you see faint red light in your OSC image under an Ha/OIII filter, it's Ha, not aurora. And of course, it can be continuum light at the Ha wavelength, not necessarily Ha itself, and light pollution can do this. But anyway it's not aurora.
Correct me if I'm wrong. As far as I know, there are many more emission lines in Aurora and some are near Ha-line. I'd guess some might fall into the filter's band., but I'm just speculating.
True, but those are few times fainter than the 6300 one, and there will also be contribution from regular airglow.
Another reason not to speculate it is aurora is that it's not uniform in your image. Aurora moves fairly quickly. Given the long integration time and the relatively narrow FoV (compared to typical aurora pictures), I would expect the aurora red light would be very uniform across the image and indistinguishable from the regular sky.
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Thanks all, and especially @Wei-Hao Wang for such a thoughtful response. It was for some of those reasons I just wasn't sure - Bortle 9 definitely has airglow, and it was not yet astronomical darkness when these were taken (although in Bortle 9 astro-dark is probably a slightly meaningless concept sadly  ). On the other hand, the filters do have a tight bandpass so a lot of the murk should have been filtered out.
It's the lack of uniform distribution that was also making me pause. What's interesting is that when I do a blink of the images, some images are much darker and others the background lightens considerably - almost as you would get with clouds but there were no clouds that night. And if I stretch just a subset of the images (those that were "lightest") this apparent nebulosity is in a different part of the sensor, suggesting it's something moving around and not a mechanical thing?
I think if I could somehow figure a way to batch stretch each light in an identical way, and then extract a common background from each, maybe then I could use PIPP to make a video that might show if the background variation across each light is the aurora flickering and moving? But batch processing and making animations is w-a-a-a-y beyond my processing skills 
I'll keep the calibrated images and see if I ever learn enough processing skills to try that in the future!
Thanks again all - v kind of you.
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Wei-Hao Wang:
Kay Ogetay:
Wei-Hao Wang:
The red of aurora comes from OI at 6300 Ang. So if you see faint red light in your OSC image under an Ha/OIII filter, it's Ha, not aurora. And of course, it can be continuum light at the Ha wavelength, not necessarily Ha itself, and light pollution can do this. But anyway it's not aurora.
Correct me if I'm wrong. As far as I know, there are many more emission lines in Aurora and some are near Ha-line. I'd guess some might fall into the filter's band., but I'm just speculating.
True, but those are few times fainter than the 6300 one, and there will also be contribution from regular airglow.
Another reason not to speculate it is aurora is that it's not uniform in your image. Aurora moves fairly quickly. Given the long integration time and the relatively narrow FoV (compared to typical aurora pictures), I would expect the aurora red light would be very uniform across the image and indistinguishable from the regular sky.
I see your point, that makes sense. Thank you.
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Thanks all, and especially @Wei-Hao Wang for such a thoughtful response. It was for some of those reasons I just wasn't sure - Bortle 9 definitely has airglow, and it was not yet astronomical darkness when these were taken (although in Bortle 9 astro-dark is probably a slightly meaningless concept sadly ). On the other hand, the filters do have a tight bandpass so a lot of the murk should have been filtered out.
It's the lack of uniform distribution that was also making me pause. What's interesting is that when I do a blink of the images, some images are much darker and others the background lightens considerably - almost as you would get with clouds but there were no clouds that night. And if I stretch just a subset of the images (those that were "lightest") this apparent nebulosity is in a different part of the sensor, suggesting it's something moving around and not a mechanical thing?
I think if I could somehow figure a way to batch stretch each light in an identical way, and then extract a common background from each, maybe then I could use PIPP to make a video that might show if the background variation across each light is the aurora flickering and moving? But batch processing and making animations is w-a-a-a-y beyond my processing skills
I'll keep the calibrated images and see if I ever learn enough processing skills to try that in the future!
Thanks again all - v kind of you.
Hi,
I think it is indeed a good idea to try to create a movie from the sequence of subs. If the red light moves, it can be a strong evidence for aurora. I have some doubt on whether this will really work, since even the subs (4 minutes, right?) are kind of very long for aurora motion. But you never know for sure until you actual create a movie. I think it will be good to try.
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