What is a characteristic effect of heavy fog in terms of atmospheric perspective?

Heavy fog serves as a classic example of atmospheric perspective, which is a technique used in art to create the illusion of depth and distance. One of the primary characteristics of fog is its ability to reduce visibility and sharpness for objects that are further away. This occurs because the fog scatters light, obscuring clarity and detail. As a result, distant forms become softer and less defined, creating a hazy effect that conveys depth. It diminishes contrast and washes out colors, further emphasizing the distance between the viewer and the obscured objects.

The other options suggest effects that do not accurately describe the impact of heavy fog. For instance, fog does not clarify distant objects; rather, it mutes them by obscuring details. It doesn't enhance color vibrancy; instead, colors may appear more subdued due to the light scattering. While fog can create a sense of depth in a composition, it does so primarily through the reduction of visibility and sharpness rather than by enhancing depth in a straightforward manner. Thus, the characteristic effect of heavy fog in the context of atmospheric perspective is predominantly about the way it reduces visibility and sharpness, leading to a more ethereal and distant appearance.