THESE TERMS ARE SPECIFIC TO GONIOAPPARENT phenomena. The definitions below are from ASTM Standard E284 [1]. They are italicized when they first appear in this chapter. annular, adj — descriptor for directional illuminating (or viewing) geometry in which the illuminator provides radiation (or the receiver possesses responsivity) that is distributed continuously and uniformly throughout the 360° of azimuth of the measurement. (See also circumferential.) anormal, adj — of angles, measured with reference to the normal to the surface. (2008)