Edges of Jupiter

[Rigel003 (Graeme)]

Not sure if this entirely belongs in this forum but you people are the most likely to notice this effect.

Looking at all the recent fantastic photos of Jupiter, the right hand side is always sharp and the left hand limb darker and less well defined. Showing my ignorance here, but is this a just photographic effect or a real feature? Is the planet in fact slightly gibbous because its so far before opposition?

[bird (Anthony Wesley)]

Yes, it's because the sun is at an angle of about 45 degrees to the planet as seen from here, the effect will decrease until opposition in June and then switch sides.

cheers, Bird

[Rigel003 (Graeme)]

Thanks, Bird. I don't tend to think of the outer planets as showing noticeable phase effects. I'd originally thought I was encountering a registration problem in Registax.

[bird (Anthony Wesley)]

Yeah, check out Mikes image from this morning and look at Io's shadow in relation to Io...

cheers, Bird

[Rigel003 (Graeme)]

Of course! It's clear from the shadow that the sun is on quite an oblique angle - no wonder the left hand limb is not fully illuminated. That's never occured to me before and I must have looked at hundreds of photos of the moon shadows. Thanks for pointing this out.