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Originally Posted by Retrograde
I was talking about the image of Io transiting - should have made that clear. 
An image I'm processing from later the same evening with Io just off Jupiter's limb also shows a lot of false colour (from dispersion I guess). The dark patches at the north & south of Io seem to disappear into the background making it look like an elongated smudge. Yeah it comes out very bright. |
You're right. It seems to have darker poles that the brighter equatorial band that make it look like an oblong dash line rather than a round shape. When it's brighter it shows a rainbow pattern but that's just chromatic.
You'd need a larger aperture to start seeing a clearer picture. Having said that it's super bright in IR against the jovian disc so easy to spot there. It's still oblong in my IR shots so 90s is definitely too long. I've also noticed that Ganymede seems to have a darker spot closer to its north pole. I thought it was an aberration before but since saw some high end shots of it and it seems real.