Three measures of this property are calibrated relative to six different A0V (“A zero five”) stars in the Johnson–Morgan system. A layer of stellar atmosphere named for this property features prominent H-alpha and Calcium II spectral lines and lies between the photosphere and the transition region. Effective temperature decreases along diagonals of a diagram named for placing measures of this property on both axes. An (*) “index” of this property computed as “B minus V” (10[1])is sometimes (10[1])used as a substitute for temperature on the x-axis of a Hertzsprung–Russel diagram. Stars enter a tract named for their size and this property near the end of the main sequence. Photometric scales measure this property that (-5[1])names classes of “dwarfs” and “giants.” For 10 points, name this property of stellar spectra that characterizes the chromosphere. ■END■ (10[1])