Posted by David Arditti at 14:07 on 2010 Mar 26
That may be part of it Andrea, but I’m not convinced it is the complete explanation, because the colours of the globe, in most imagers’ images, around opposition, are really quite different to the colours away from opposition, as seen here. The effect is more than just an intensity change.I have done various observations to test the Opposition Effect of Saturn over the last 3 apparitions. In 2008 I concluded that the brightness of the rings increases most in the UV and IR, somewhat in the blue, and hardly at all in the red and green (I published a note on this, with images, in the Journal, April 2008). Now, assuming that the CCD filters that observers use are effectively blocked against UV and IR, this means that, in images, the rings should become blue-er near opposition. But I think actually imagers generally balance the colours so that the rings look white. This process would be expected to relatively suppress the blue in the globe, and make it redder or yellower. But what we are seeing is not quite this either. In fact I have found that no balance of the channels can make the globe colours look normal at opposition. So I am not decided whether this effect is something to do with the characteristics of filters, if if something more "real" is going on here.