Posted by Andrea Tasselli at 10:41 on 2010 Mar 27
Hi David,I don’t know about other imagers but I have imaged Saturn since 2001 and it never occurred to me that it changed colours at (around) oppositions. As for the current one (I missed the past apparition’s) I’m pretty sure it didn’t change colours, by and large. Fact is that *measuring* photometric changes in saturn’s globe is devilishly difficult and full of traps and catches. I tried to keep track of relative response of rings and globe in various colour bands (I think from 2004) but it is difficult to come down to hard facts. Certainly if such a thing does really happen any factual assessment can’t be based on the fancies of this or that imager. Besides, I can’t think of any reasonable physical explanation for the purported colour changes.Andrea T.