Note that altitude in this sense is measured in angular degrees, and has nothing to do with height above the ground or elevation above sea level. Altitude-Azimuth coordinates uniquely specify a given point with respect to an observer's horizon at an indicated time. Use a protractor outdoors to estimate the altitude of Polaris, or to measure degrees of azimuth along the horizon from due north. Horizon coordinates vary with locality , but are still useful in skywatching and are used with many telescope mounts. Any star or planet located on the meridian is said to be at meridian transit or culmination .
Circumpolar stars cross the meridian twice each day without setting below the horizon.
Only the higher transit of the two would be a culmination. When a planet or star is transiting the meridian it is at its highest in the sky and therefore its farthest from dust and horizon haze. The best time to see it, then, would be around its midnight culmination. Rises in the east when the sun sets in the west. Transits the meridian at midnight.