What does the phenomenon of "bobbing a light" refer to?

The phenomenon of "bobbing a light" refers to the effect that occurs when the observer's eye is alternately raised and lowered due to the motion of the vessel. When the eye level is changed significantly, typically by several feet, the appearance of the light can vary, making it seem as though it is moving up and down in the observer's line of sight. This effect can be especially pronounced in choppy seas where the boat's movement is more pronounced.

In contrast, seeing a light on the horizon while moving does not necessarily relate to the bobbing action; it's simply a situation where a mariner observes a light from a distance. Changing the angle of the light source does not pertain to the motion of the vessel either. Understanding the mechanics behind how a light appears to bob due to the vessel's movement is key for navigators, as it affects their perception of distance, altitude, and bearing of the light during navigation.