sentences:  formula_1,
  
  with formula_2 being the material's index of refraction (not the Bravais index of refraction for inclined rays).However, many more features give a structure to the intensity pattern of the parhelic circle.Among the features of the parhelic circle are the Liljequist parhelia, the 90° parhelia (likely unobservable), the second order 90° parhelia (unobservable), the 22° parhelia and more.