The difference (measured in degrees) between the GHA of the body and the longitude of the observer is the __________.

Correct Answer: Option B — meridian angle

Meridian angle ($t$ or $M$), defined in Bowditch, is the arc of the celestial equator measured eastward or westward from the local meridian to the hour circle of the body, equivalent to the algebraic difference between GHA and the observer's longitude.