名詞 ras:

1. the network in the reticular formation that serves an alerting or arousal function
   同義詞：reticular activating system

名詞 ra:

1. an intensely radioactive metallic element that occurs in minute amounts in uranium ores
   同義詞：radium, Ra, atomic number 88
2. ancient Egyptian sun god with the head of a hawk; a universal creator; he merged with the god Amen as Amen-Ra to become the king of the gods
   同義詞：Ra, Re
3. (astronomy) the equatorial coordinate specifying the angle, measured eastward along the celestial equator, from the vernal equinox to the intersection of the hour circle that passes through an object in the sky; usually expressed in hours and minutes and seconds; used with declination to specify positions on the celestial sphere
   同義詞：right ascension, RA, celestial longitude