🚀 go-pugleaf

> In article <1730001@hpislx.HP.COM> gvg@hpislx.HP.COM (Greg Goebel) writes:
>>"Spectral Resolution" for FIRAS:
>>   0.2 cm^-1
 
From article <1990Jan14.233158.9704@utzoo.uucp>, by 
henry@utzoo.uucp (Henry Spencer):
> Looks fine to me.  The spectroscopists have this curious habit of using
> waves per unit length ("wavenumber") rather than length per wave (normal,
> conventional "wavelength").  

Right so far; wavenumber is useful because it is essentially a
frequency unit.  It just has the speed of light divided out.  The unit
even has an official name ("kayser"), which is seldom used. 

> A wavenumber resolution of 0.2 cm^-1 is a wavelength resolution of 5cm.

This part was a bit too hasty.  Wavenumber resolution of 0.2 cm^-1 is a
frequency resolution of 6x10^9 Hz (in vacuum; very slightly different
in air).  The corresponding wavelength resolution depends on the
wavelength (or frequency) being observed.  The correct formula can be
found by setting dw/w = dW/W, which leads to dW = dw/w^2, where dW is
wavelength resolution, dw is wavenumber resolution, and w is
wavenumber and W is the wavelength.  (It's really easy to get confused,
though; I had to write the conversion formulas down even though I work
with these units all the time.)  I forget exactly what the wavelength
for FIRAS is, but I think it is about 1 mm or 10 cm^-1.  The spectral
resolution stated would then correspond to 0.02 mm.
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