From: rrllff@yahoo.com   
      
   On Thursday, November 7, 2013 1:18:39 PM UTC-5, Louis Boyd wrote:   
   > laser wrote:   
   >   
   > > All the wavelength will be measured in air.   
   > > Do you know the reason that there is an option to change wavelength from   
   air to vacuum?   
   >   
   > The spectroscopes here at Fairborn Observatory  (and many others) are   
   >   
   > operated in a > 10-6 Torr vacuum. We're measuring stellar radial   
   > velocities for planet searchs to less than 1 meter/second. The   
   > spectroscopes are also cooled and temperature stabilized to better than   
   > .01 degree kelvin.   Having the variable index of refraction of the air   
   > inside  the spectroscope to deal with would be an unacceptable and   
   > unnecessary source of error.  It's hard enough to deal with the the   
   > constantly changing velocity vector of the Earth.   
   >   
   > Your statement that "All the wavelength sill be measured in air" is   
   > simply false.   
      
   This isn't my field.  However, wouldn't using   
   frequency instead of wavelength remove all   
   ambiguities?   
      
   http:www.richardfisher.com   
      
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