🔍 Key Concepts

• Celestial sphere and how it relates to an observer on Earth • Definition of zenith in basic celestial navigation/astronomy • Relationship between the observer’s position and points like poles, horizon, and overhead

💭 Think About

• Which point on the celestial sphere is unique to each observer at a given time? • Which option describes a point that moves with the observer, rather than being fixed to Earth locations like Greenwich or the poles? • How is the zenith positioned relative to the local horizon: along it, near it, or at right angles to it?

✅ Before You Answer

• Be sure you know that the zenith is defined relative to the observer, not a fixed place on Earth • Check which choice describes a point straight up from where you are standing, rather than east, west, or at the poles • Confirm that the angular distance between the zenith and any point on the true horizon is 90°