In field astronomy, the quantities observed are entirely A. Lengths B. Angles C. Heights D. All of these

The correct answer is: D. All of these

In field astronomy, the quantities observed are entirely lengths, angles, and heights.

• Lengths are used to measure the distances between objects. For example, the distance between two stars can be measured by using the parallax method.
• Angles are used to measure the positions of objects relative to each other. For example, the angle between two stars can be measured by using a sextant.
• Heights are used to measure the elevations of objects above a reference level. For example, the height of a mountain can be measured by using a clinometer.

All of these quantities are important in field astronomy because they allow astronomers to determine the positions, distances, and sizes of objects in space.