Assertion: emission nebula | /r/CapableOf | glow as a result of excitation
Facets:
value: by stars of spectral class o
type: CAUSE
Source sentences:
text: They glow as a result of excitation by stars of spectral class O (see SPECTRAL CLASSIFICATION OF STARS ), which have a surface temperature of 25,000°-50,000°K and a mass of about ten times that of the sun.