Definition of the true/rational/celestial horizon What is the plane that is perpendicular to the zenith–nadir (vertical) line and passes through the Earth’s center called?

Introduction / Context:Several equivalent terms exist in astronomy and geodesy for the reference plane perpendicular to the observer’s vertical. Knowing these synonyms avoids confusion when consulting different texts or instrument manuals.

Given Data / Assumptions:

• Zenith–nadir line defines the local vertical at the observer’s position.
• The reference plane is normal to this vertical and conceptually passes through the Earth’s center.
• We focus on naming equivalence used in surveying astronomy.

Concept / Approach:The plane perpendicular to the observer’s vertical and passing through Earth’s center is known variously as the rational horizon, the true horizon, or the celestial horizon. All three terms refer to the same fundamental plane used to measure altitudes and define horizon coordinates.

Step-by-Step Solution:Identify the geometric construction: plane ⟂ to vertical through Earth’s center.Recognize the accepted synonyms in surveying–astronomy literature.Therefore, all listed names are correct.

Verification / Alternative check:Star altitude is measured above this horizon plane; it is the basis for altitude–azimuth systems across references, confirming terminological equivalence.

Why Other Options Are Wrong:Each individual label is accurate; hence the comprehensive choice “All of the above” is correct. “None” is incompatible with standard terminology.

Common Pitfalls:Misusing “apparent” or “sensible” horizon, which involve atmospheric refraction and observer’s eye height; those are different concepts from the rational/true/celestial horizon.

Final Answer:All of the above