Meridian altitude refers to the angle of an astronomical object (such as a star or planet) above the observer's horizon when that object is at its highest point in the sky, which occurs when it crosses the local meridian. The local meridian is an imaginary line that runs from true north to true south, passing directly overhead, and is aligned with the observer’s zenith. At this moment, the object's altitude is measured as the vertical angle between the object and the observer's horizon.
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