a source of something emits / produces / generates / provides that something & a star is a source of light / light energy through nuclear reactions ->  a star emits light through nuclear reactions  a star emits light through nuclear reactions & a star is a kind of celestial object / celestial body ->  a star is a celestial body that emits light through nuclear reactions  a star is a celestial body that emits light through nuclear reactions & astronomical is similar to celestial -> a star is an astronomical body that emits light through nuclear reactions