Which of the following is the reference point to measure an azimuth angle for a body?

Correct Answer: Option C — observer's meridian

The azimuth angle of a celestial body is measured along the horizon from the observer's meridian. It represents the arc of the horizon between the observer's meridian and the vertical circle passing through the body. This is a fundamental concept in celestial navigation as defined in Bowditch, The American Practical Navigator.