Cosmological Distances

• PROPER DISTANCE or light travel distance:
  
  
  Lookback time:
  
  
• COMOVING DISTANCE or line-of-sight comoving distance (in Weinberg Proper distance):
  
  
  Proper distance divided by the scale factor
  
  
• LUMINOSITY DISTANCE:
  
  
  d_M=transverse comoving distance (Hogg 1999)
  In a FLAT universe d_M=d_C (:=line-of-sight comoving distance). It implies: