Sum of Angles | # of lines | Circumference/radius | |
Flat | 180 | 1 | twice pi |
Positive | > 180 | none | less than twice pi |
Negative | < 180 | infinite | greater than twice pi |
Very simply:
HOT GAS, FAST ELECTRONS, SHORT WAVELENGTH, BLUE : Rigel
COOL GAS, SLOW ELECTRONS, LONG WAVELENGTH, RED : Betelgeuse