[[Mod. note --   
   A3: Please.   
   Q3: Should I avoid top posting on this newsgroup?   
      
   A2: Because, by reversing the order of a conversation, it leaves the   
       reader without much context, and makes them read a message in an   
       unnatural order.   
   Q2: Why is top posting irritating?   
      
   A1: It is the practice of putting your reply to a message before the   
       quoted message, instead of after the (trimmed) message.   
   Q1: What is top posting?   
   -- jt]]   
      
   THANK YOU VERY MUCH FOR YOUR ANSWER.   
      
   The incoherence of stars light means that there is a stochastic   
   phase function of time which breakes its coherence? I wander to   
   which extent the stars light can be considered coherent (for short   
   times?), since I understand that coherence is necessary for   
   interferometry with star lights.   
      
   Thanks   
      
   On Tuesday, February 6, 2018 at 10:14:34 PM UTC, Jos Bergervoet wrote:   
   [[Mod. note -- 28 excessively-quoted lines snipped here.  -- jt]]   
   > Sun, with magnitude of -27: irradiation = 1kW/m^2 (below atmosphere).   
   >   
   > One magnitude step is 4 dB, is 10^0.4 times less power. Bright stars   
   > have magnitude around 0, so 10^(-27*0.4) * 1000 W/m^2   
   >   
   > This power density is E-field squared divided by wave impedance,   
   > the latter is mu0*c ~= 367 Ohm. So E-field strengths: (approximately)   
   >   
   >    magnitude -27  ==>  600 V/m    (Sunlight)   
   >    magnitude   0  ==>  2.5 mV/m   (One star of top-5 of brightest sta=   
   rs)   
   >    magnitude   6  ==>  150 uV/m   (Weakest stars the eye can see)   
   >   
   > Incidently, the signal from a radio station is also in the order   
   > of 100 uV/m. (Of course sensitive receivers can detect much weaker   
   > signals, just like big telescopes can see much fainter stars).   
   >   
   > These are amplitudes of the total EM signal, all frequencies   
   > (wavelengths) added together to one time-dependent E-field.   
   >   
   > --   
   > Jos   
      
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