Greenwich Hour Angle (GHA) is defined as

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Multiple Choice

Greenwich Hour Angle (GHA) is defined as

GHA is the angular distance measured westward from the Greenwich meridian to the hour circle of a celestial body. Using Greenwich as the reference point makes GHA a westward measure that ties celestial positions to the familiar longitude system, and it’s used together with the observer’s longitude to find the local hour angle and, ultimately, the altitude for sight reductions. So the correct description is the angular distance west of the Greenwich meridian. The other options describe different quantities: measuring east instead of west isn’t GHA; the angle between the body and the zenith is the zenith distance, not GHA; and the altitude above the horizon is simply the altitude, not GHA.

GHA is the angular distance measured westward from the Greenwich meridian to the hour circle of a celestial body. Using Greenwich as the reference point makes GHA a westward measure that ties celestial positions to the familiar longitude system, and it’s used together with the observer’s longitude to find the local hour angle and, ultimately, the altitude for sight reductions.

So the correct description is the angular distance west of the Greenwich meridian. The other options describe different quantities: measuring east instead of west isn’t GHA; the angle between the body and the zenith is the zenith distance, not GHA; and the altitude above the horizon is simply the altitude, not GHA.

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