Spherical astronomy basics — meridian, altitude, and zenith distance Which of the following statements about an observer’s meridian plane and star altitude are correct?

Introduction / Context:
Field astronomy in surveying uses celestial sphere concepts to determine direction, latitude, and time. Key angles include altitude, azimuth, and zenith distance, and the meridian plane defines reference directions.

Given Data / Assumptions:

• Observer’s local vertical (through zenith) and celestial pole are known constructs.
• Angles are measured at the station.

Concept / Approach:

The observer’s meridian is the great circle through the zenith and celestial poles. Altitude is the angle above the horizon; equivalently, the angle between the star’s projection in the vertical and horizontal directions at the observer. Zenith distance equals 90° minus altitude.

Step-by-Step Solution:

Verification / Alternative check:

Standard surveying/astronomy texts present these definitions consistently.

Why Other Options Are Wrong:

• The combined option is most accurate since each statement is true.

Common Pitfalls:

• Confusing azimuth (bearing in the horizontal plane) with altitude (elevation).

Final Answer:

All of the above.