[HN Gopher] Seeing Triple (Annotated)
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       Seeing Triple (Annotated)
        
       Author : pallas_athena
       Score  : 94 points
       Date   : 2023-04-24 14:05 UTC (8 hours ago)
        
 (HTM) web link (esawebb.org)
 (TXT) w3m dump (esawebb.org)
        
       | bobbylarrybobby wrote:
       | Also fascinating is that celestial bodies that get duplicated by
       | lensing always produce an odd number 2n+1 of images, n of which
       | are inverted and n+1 of which are upright. I won't pretend to
       | understand why this is.
       | 
       | https://en.m.wikipedia.org/wiki/Odd_number_theorem
        
         | LoganDark wrote:
         | Non-mobile link:
         | https://en.wikipedia.org/wiki/Odd_number_theorem
        
         | kmill wrote:
         | A handwavy argument for this is that if you continuously deform
         | your picture, you can bring an upright and an inverted image
         | toward each other until they cancel out (if you've ever played
         | around with curved mirrors you probably can imagine how that
         | would look). Eventually, after doing enough of these
         | cancelations, you're left with an undistorted picture with a
         | single upright image -- so, you must have had n inverted images
         | and n+1 upright ones. The morse theory the wikipedia article
         | mentions is roughly about being able to do this argument
         | rigorously.
        
       | tomcam wrote:
       | I hate it when the universe just cuts and pastes instead of
       | spawning a new galaxy like the rest of us would
        
       | Cthulhu_ wrote:
       | See also: Einstein Ring [0], where a light source passes
       | 'through' a strong gravitational source which refocuses the light
       | spreading out, and the Einstein Cross [1], similar, but where the
       | light source (a quasar) passes a gravitational source and shows
       | up as four points of light "due to the elongated shape of the
       | lensing galaxy and the quasar being off-centre"
       | 
       | [0] https://en.wikipedia.org/wiki/Einstein_ring
       | 
       | [1] https://en.wikipedia.org/wiki/Einstein_Cross
        
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       (page generated 2023-04-24 23:01 UTC)