During astronomical observations with a theodolite or transit, which directional references are the observer primarily concerned with?

Introduction / Context:
Astronomical observations in surveying (e.g., determining azimuths, latitude, and time) require careful orientation of the instrument and a clear understanding of reference directions in the celestial sphere. Correctly aligning these directions ensures that observed angles reduce to meaningful geodetic quantities.

Given Data / Assumptions:

• The observer uses a precise instrument (theodolite, transit, or total station with astronomical capability).
• The celestial sphere model is employed: poles, equator, zenith, and nadir.
• Local vertical is established by the instrument’s leveling (plumb line or spirit/tilt sensors).

Concept / Approach:
Three directional references matter simultaneously: (1) the local vertical, defining the sensible horizon and the instrument’s rotation axis; (2) the celestial poles, aligning with Earth’s rotation axis and enabling conversion between hour angle and azimuth; and (3) the line of sight to the star, defining the observed altitude and azimuth of the body.

Step-by-Step Solution:
Establish the vertical by careful leveling to set the instrument’s axis.Relate the instrument orientation to the celestial poles (north/south) for azimuth reference.Sight the target star; record the star’s direction (altitude/azimuth or hour angle/declination).

Verification / Alternative check:
Reduction formulas for astronomical azimuth rely on the instrument’s vertical orientation, pole direction, and the star’s observed direction; all three must be known or inferred.

Why Other Options Are Wrong:

• Each individual direction is necessary; the correct comprehensive answer is therefore ‘‘all the above.’’

Common Pitfalls:

• Neglecting instrument leveling causes azimuth and altitude errors.
• Failing to account for polar reference (latitude) leads to incorrect reductions.

Final Answer:
all the above