From: nmm1@cus.cam.ac.uk   
      
   In article <72d32143.0405081423.3115a96f@posting.google.com>, ve   
   emite@dualboot.net (Christopher M. Jones) writes:   
   |> cray74@hotmail.com (Mike Miller) wrote in message news:<5dcb4   
   db.0405061609.78da1818@posting.google.com>...   
   |> > What is the threshold of brightness for seeing an astronomical object   
   |> > in the daytime Earth sky?   
      
   This part of your question isn't well phrased, I am afraid.  It   
   depends immensely what you mean by 'the daytime Earth sky'.   
   Depending on conditions, Venus may be visible, or the sun may   
   be invisible.  There is a lot of variation even in cloudless   
   skies - it isn't rare to be unable to feel the heat of an   
   unobscured sun, for example.   
      
   |> > Specifically, would a star with 70% of Sol's absolute brightness be   
   |> > visible at 45 AU?   
   |>   
   |> Yes.  It would be hundreds of times brighter than a   
   |> full moon.   
      
   In almost all cloudless skies, yes, but I have seen conditions   
   hazy enough that a full moon was effectively invisible.  It is   
   possible that they can be much more extreme.   
      
      
   Regards,   
   Nick Maclaren.   
      
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