Back to forums

Deep sky imaging during an Aurora… keep subframes or throw them out?

Pleiades Astrophoto PixInsight Steffen Hirtle GraXpert Acquisition Light Pollution Deep Sky
12 replies•344 views
Robert Lowenthal avatar
Robert Lowenthal avatar
As I’m writing this, we’re experiencing an Aurora with Kp index at ~ 8 in central Illinois. The sky is definitely brighter, with SQM readings ranging from 18.6 to 20.2. In my Bortle 4 backyard, I usually see SQM readings around 20 to 21.

I’m concerned that the aurora doesn’t make the sky uniformly brighter, but might rather form bands, like I see when I took a photo with my iPhone . Will the subframes that I am taking tonight interfere with subframes that I’ve taken from other nights without aurora, after stacking them in PixInsight WBPP? Any hope that a gradient removal tool (I use GraXpert) could remove the aurora artifacts?

Looking for advice… Should I discard the subframes from tonight, or keep them? 

Thank you,
Robert
Well Written Insightful Respectful Engaging
HR_Maurer avatar
HR_Maurer avatar
Discard, if not narrowband.

I would switch to ultra short focal length with large aperture during aurora, and go for those. Some seconds exposure time. For me, Aurorae at home are very rare.
But when you did Deep Sky imaging, your field of view was very narrow and your subs exposure time was minutes. I wouldnt expect any significant bands, maybe gradients, but bright background hard to color calibrate. In case of narrowband you might have no issue.
Robert Lowenthal avatar
Robert Lowenthal avatar
I am imaging in Narrowband tonight. The subframes look good. FOV is 3 x 2 degrees. Exposures are 300s. 

Later tonight, I’ll be taking 60s RGB subframes for the stars. I’m hoping that will be ok, as I’m going to discard the starless RGB image.
Well Written
Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
It will affect everything, been there tried that smile

Agree with the above, when those lights are active, let your rig have the night off and enjoy the show/use a wide angle lens.​​​​


Edit: I would definitely not keep them.
Dunk avatar
Dunk avatar
I'd use whatever you used in the screenshot above and take some more aurora shots!
James Peirce avatar
James Peirce avatar
I haven’t had to deal with an intense Aurora, given I am in Utah, United States. But for the more moderate interference I’ve had in images, which can show up as waves of some color transitioning through them, I have found using local normalization in PixInsight with a large quantity of images from the session combined to create the reference image, has been effective in converting the Aurora to the equivalent of a fairly linear light gradient, that can quite effectively be modeled out.
Helpful
andrea tasselli avatar
andrea tasselli avatar
I had to stop tonight as the sky was too bright even for NB. If the subject was bright and the FOV narrow I'd say keep and use LN to a reference without issues otherwise chuck.
TiffsAndAstro avatar
TiffsAndAstro avatar
Didn't seem (but it might have) effected my m31 last night but around 1130 I switched to m45 to avoid meridian flip (don't ask) and I have red in those subs.
And they look like crap smile

NW England here 52n
Tony Gondola avatar
Tony Gondola avatar
I think that no matter what you do, it's not going to be optimal, Astrophotography is hard enough without having to contend with varying sky brightness and color throughout the integration.
Oskari Nikkinen avatar
Oskari Nikkinen avatar
If you have enough data from clean nights the stack will mostly average out the Aurora, provided that the light show wasnt bang on in the middle of your frame and you exposed long enough for the movement of the aurora to even out. So, could be ok could be bad.

I am imaging from 60N and there are a few nights each year that have aurora in the stack. Often i can get away with it, but sometimes its too much and an hour or two at the peak have to get scrapped.
Helpful Engaging Supportive
Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
Tony Gondola:
I think that no matter what you do, it's not going to be optimal, Astrophotography is hard enough without having to contend with varying sky brightness and color throughout the integration.

I agree. Using sub-optimal data or working out ways to include data that is compromised is just a no-go for me. Too much time and resources go into getting those images, so I would never accept having bad frames thrown in there. It will have an impact somehow. But to each their own, based on my own experience I let my scopes rest on these nights.

I'm above 60N and while the northern lights are much more common further north, they are increasingly more common around here as well during solar maximum. Even if they seem dim and barely visible by eye sometimes , which they did for me last night, they still cover the sky more or less in varying degree throughout the night. This was just a 15s test exposure with a fisheye to see how much of it there were. If I were to do a 500s exposure it would be completely ruined (NB or not). By eye I could barely make out faint light streaks where the pink ones are located in the image. The sky otherwise generally just looked bright, sort of like moonlight. 
Helpful Insightful Respectful Engaging
astroyyc avatar
astroyyc avatar
I’m doing NB at 1600mm FL, it’s still worth stacking.
Robert Lowenthal avatar
Robert Lowenthal avatar
Tony Gondola:
I think that no matter what you do, it's not going to be optimal, Astrophotography is hard enough without having to contend with varying sky brightness and color throughout the integration.

I agree with what you and @Jan Erik Vallestad said. I have over 20 hours into imaging The Ghost of Cassiopeia. I’d like to get that to over 30 hours. Last night would have added another 8 hours, but there is a lot of faint, wispy Ha data that I don’t want to corrupt. I’m using a QHY600M, so processing full-frame subframes and fiddling with it to try to incorporate last night’s data would be time consuming. I’m ok with tossing out last night’s imaging session, especially as this target is in a good position for me for another month.
Well Written