;+
; NAME:
;  geocllh2xyz
; PURPOSE: (one line)
;  Convert geocentric latitude, longitude, and height to cartesian coordinates
; DESCRIPTION:
;  Convert geocentric latitude, longitude, and height to cartesian coordinates
; CATEGORY:
;  Astronomy
; CALLING SEQUENCE:
;  geocllh, lat, long, h, x, y, z
; INPUTS:
;  
;  
; OPTIONAL INPUT PARAMETERS:
;  none
; KEYWORD INPUT PARAMETERS:
;  none
; KEYWORD OUTPUT PARAMETERS:
;  none
; OUTPUTS:
;  Planck function
; COMMON BLOCKS:
;  uses share_physconst
; SIDE EFFECTS:
; RESTRICTIONS:
;  Must run phys_const first
;  For now, T and nu are scalars
;  Doesn't check if h nu/k T << 1
; PROCEDURE:
; MODIFICATION HISTORY:
;  Written 2000 April, by Leslie Young, SwRI
;-

function planck_nu, t, nu

common share_physconst
 c = speed_of_light & h = planck_constant & k = boltzman_constant
 e = h*nu ; energy of a photon
 
 b = 2. * (e) * (nu/c)^2. / ( exp( e / (k*t) ) - 1. )
 
 return, b
end

pro planck_nu_test
common share_physconst
c = speed_of_light
rs = 695265.e5 ; radius of sun in cm
au = 1.496e13 ; AU in cm
  t = 5770.
  lam_mu = findgen(1000)*0.01 + 0.1
  invcm = 1.e4/lam_mu
  nu = c * invcm
  b = fltarr(1000)
  for i=0,999 do b(i) = planck_nu(t, nu(i))
  plot, lam_mu, b * (nu/lam_mu) * !pi * (rs/au)^2. * 1.e-3, xr=[0,4]
end