Atmosphere or Artifact? Venus transit image

[owlice]

APOD reader Paul Klauninger writes:

I was trying to determine if light scatter through the atmosphere of Venus could be imaged once the planet was completely silhouetted on the Sun. The seeing was very stable at our observing site in a remote part of central Ontario, Canada. I performed some high-resolution imaging using an imager with very small (2.2 micron) pixels on a 150mm F12 Maksutov-Cassegrain telescope at prime focus and using a Thousand Oaks glass solar filter. I was amazed to see that the raw images clearly showed a ring of light around the planet. This final image is a stack of 72 raw images, with minimal processing.

To try and determine whether this ring was in fact the atmosphere or some sort of an imaging artifact, I compared it to a hi-res frame taken at almost the same moment by NASA's SDO (insert on right). The SDO image also clearly shows a ring at the circumference. The SDO ring is much thinner, which is what you would expect with ultra-quality optics that are completely removed from the distortions of our atmosphere. So the question remains ... is this the atmosphere of Venus or an imaging artifact of some sort?

And here are the images he sent:

[attachment=1]Venus Transit hi-res_2012June05_Paul Klauninger-1.jpg[/attachment]

[attachment=0]Venus Transit hi-res with NASA SDO insert_2012June05_Paul Klauninger-1.jpg[/attachment]

Is the ring Venus's atmosphere? Or an artifact?

[Chris Peterson]

APOD reader Paul Klauninger writes:

I was trying to determine if light scatter through the atmosphere of Venus could be imaged once the planet was completely silhouetted on the Sun. The seeing was very stable at our observing site in a remote part of central Ontario, Canada. I performed some high-resolution imaging using an imager with very small (2.2 micron) pixels on a 150mm F12 Maksutov-Cassegrain telescope at prime focus and using a Thousand Oaks glass solar filter. I was amazed to see that the raw images clearly showed a ring of light around the planet. This final image is a stack of 72 raw images, with minimal processing.

To try and determine whether this ring was in fact the atmosphere or some sort of an imaging artifact, I compared it to a hi-res frame taken at almost the same moment by NASA's SDO (insert on right). The SDO image also clearly shows a ring at the circumference. The SDO ring is much thinner, which is what you would expect with ultra-quality optics that are completely removed from the distortions of our atmosphere. So the question remains ... is this the atmosphere of Venus or an imaging artifact of some sort?

Is the ring Venus's atmosphere? Or an artifact?

I think it's an artifact. I'm not convinced that the SDO continuum images show atmosphere, either. The only images I've seen that convincingly show a ring were narrowband. Getting this from the ground with a highly oversampled imaging system (0.25"/pixel with the diffraction limit being about 4", and the seeing probably close to that, as well) seems very unlikely. In addition, the color seems wrong.

My first question in studying an image like this would be, what does a completely unprocessed single frame look like? Stacking is more than "minimal processing", and introduces many opportunities for artifact generation.