Ags Posted June 22, 2021 Share Posted June 22, 2021 I do like a good APOD and today's is an amazing close in view of a planetary system being formed, combining visual and IR light. https://apod.nasa.gov/apod/ap210622.html The star HD 163296 is an A1V star about 330 light years away.. That dust ring looks about 200 AU across which means that it is 2 arcseconds wide. Pretty sharp optics from ALMA! Also the polar jets imaged in visible light - it seems to me to be undersampled - I wonder how big the pixels were? 2 Link to comment Share on other sites More sharing options...
vlaiv Posted June 22, 2021 Share Posted June 22, 2021 It says that telescope has angular resolution of 0.2 arc seconds for imaging and has 120m focal length (VIMOS instrument capable of imaging in 300-1000nm range - not sure if that was used). That would make pixel size - ~116µm. Link to comment Share on other sites More sharing options...
Ags Posted June 24, 2021 Author Share Posted June 24, 2021 That agrees with what I see in the image, but the visible light channel looks really undersampled... Link to comment Share on other sites More sharing options...
vlaiv Posted June 24, 2021 Share Posted June 24, 2021 It will certainly be "undersampled" compared to ALMA which has 0.01" resolution - or about x20 higher than VLT. Link to comment Share on other sites More sharing options...
Ags Posted June 26, 2021 Author Share Posted June 26, 2021 I am not explaining myself well. I am not comparing the visual channel to the ALMA channel which benefits from massively more aperture. I am comparing the visual channel with itself - it is so blocky with such stark jumps in brightness between adjacent pixels, I just seems to me they could have got away with smaller pixels. Link to comment Share on other sites More sharing options...
vlaiv Posted June 26, 2021 Share Posted June 26, 2021 2 minutes ago, Ags said: I am not explaining myself well. I am not comparing the visual channel to the ALMA channel which benefits from massively more aperture. I am comparing the visual channel with itself - it is so blocky with such stark jumps in brightness between adjacent pixels, I just seems to me they could have got away with smaller pixels. But if you look at this version - I think it's all fine: If you have such large mismatch in resolution between two images and you want to make compound image - well, you need to rescale one of them to match their scales. You can either loose detail in more resolved one - or simply make less resolved one look bad - without detail. Fact that these two telescopes have very different resolving power - order of magnitude different - makes it hard to match resolutions and hence - one source needs to suffer. Authors chose visual to be largely scaled up to match resolution of radio and that made visual channel look bad - but it is not bad itself when viewed at proper scale to itself. Link to comment Share on other sites More sharing options...
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