Field astronomy in surveying — what is actually observed? In routine field astronomy applied to surveying, the directly observed quantities are primarily:

Introduction / Context:
Field astronomy provides direction, time, and latitude/longitude control for geodetic work. Theodolites and total stations are employed to sight celestial targets and measure angular relationships precisely.

Given Data / Assumptions:

• Classical astronomical surveying with optical instruments.
• Derived quantities (time, position) come from angular measurements and known ephemerides.

Concept / Approach:

Observers measure horizontal and vertical angles to stars or the Sun (e.g., altitude and azimuth), then compute positions or time. Lengths and heights are not measured directly by astronomical observation; they are derived via geometry, leveling, or distance measurements unrelated to celestial sighting.

Step-by-Step Solution:

Verification / Alternative check:

Methodologies such as Laplace azimuths, astronomical latitude by meridian altitude, and time determinations all center on angles.

Why Other Options Are Wrong:

• Lengths and heights may be outcomes of separate surveying operations, not of astronomical observations themselves.

Common Pitfalls:

• Confusing theodolite angle observations with EDM distance measurements; the latter are not “astronomy”.

Final Answer:

Angles.