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Image of the day 07/23/2019

    Saturn: the Seeliger Effect 28th June versus 9th July, 


            Niall MacNeill

    Saturn: the Seeliger Effect 28th June versus 9th July

    Technical card

    Resolution: 4000x2325

    Locations: Home property, Wattle Flat, NSW, Australia

    Data source: Backyard


    I imaged Saturn one day short of opposition on July 9th. I was astounded by its appearance with the rings being so bright compared to what I am used to. I realised that this is due to the Seeliger Effect, named for the man, Hugo von Seeliger, who first proposed the explanation of the sudden surge in brightness of the rings around opposition. This is my 4th year of imaging the planets and yet somehow I had always missed the opportunity to see and image Saturn at this time. The effect was much more pronounced than I had expected.
    So here is my understanding of it. The rings are made up of countless chunks of ice and they are orbiting in close proximity to their neighbours. So close in fact that their shadows fall onto these neighbouring chunks. When seen from the side, as we see the rings before and after opposition, the reflected light is diminished because a proportion of the chunks' surfaces visible to us are in shadow. This dims the appearance of the rings. However at opposition we are seeing the fully lit face of each chunk and their shadows go directly behind them. Where they fall on another chunk we don't see that surface anyway because it is obscured by the chunk in front. Effectively every visible face is fully lit and as a consequence the rings brighten appreciably. There will also be some effect due to the angle of the reflected light per Lambert's Law.
    So how great is the effect? I decided it would be interesting to compare two images with and without the effect. The first was captured only 11 days earlier on 2019-06-28_1328 UT before the more recent one on 2019-07-09_1334 UT. Unfortunately the seeing wasn't as good for the second capture and so the planet's features and banding are not as well resolved, but that doesn't detract too much from the comparison.
    I resized the images so they were identical, even though the difference was small. I also matched the brightness of the planet so the comparison is fair.
    And so here it is......the Seeliger Effect.



    Niall MacNeill
    License: None (All rights reserved)


    Saturn: the Seeliger Effect 28th June versus 9th July, 


            Niall MacNeill