ze·nith

– noun
1. the point on the celestial sphere vertically above a given position or observer.
2. a highest point or state; culmination.

na·dir

– noun
1. the point on the celestial sphere directly beneath a given position or observer and diametrically opposite the zenith.
2. the point of a horoscope opposite the midheaven.
3. the lowest point; point of greatest adversity or despair.