Hi Jen,
If you'd like to have another attempt at stacking your corona exposures I recommend this guide:
http://www.aldebaran.cz/actions/2006...phseclipse.pdf
I followed it for the first 5 steps using GIMP and got a reasonable result. I found the masking steps (steps 6-9) tedious to get a clean, even image so I used a couple of filters in G'MIC instead to blend the frames.
These are the steps I followed using GIMP based on the PDF guide:
1. Opened each image a layer, starting off with the shortest exposures. Renamed each layer accordingly.
2. Turned off all layers except for the bottom two and used the Difference mode on the top active layer and moved it over the bottom one. Rinsed and repeated with all the exposures, aligning them all to the bottom layer.
3. Used a GIMP plugin called G'MIC-Qt to blend the exposures (Filters --> G'Mic --> Layers --> Blend [Median]. Remember to select all input layers under the Input/Output section and output as new layer.
4. Used G'MIC again do to an unsharp mask (G'MIC --> Details --> Sharpen [unsharp mask].
You should be able to stop here and have a fairly good image. I wanted to reduce the brightness of the inner corona so I did this using a layer mask using a copy of one the base exposure layers. I've just tried replicating this step but I can't remember exactly how I did it (it was over a month ago).
Hope this helps.
Cheers