In meteorological observation, how is a "clear sky" defined?

A "clear sky" is defined in meteorology as when less than 1/8th of the sky is covered by clouds. This definition implies that there is a predominant lack of cloud presence allowing for more sunlight to reach the surface and typically indicates favorable weather conditions.

When less than 1/8th of the sky is cloudy, the sky is perceived as mostly clear, which is why this definition is widely accepted among meteorologists and utilized in weather observations and reporting. This standard helps in maintaining consistency in weather data collection and communication, ensuring that terms like "clear sky" convey reliable information.

The other options do not accurately reflect the meteorological definition of a clear sky. For example, stating that there is no cloud cover at all would imply an unrealistic level of perfection in the definition, as atmospheric conditions can vary slightly even in what is observed as a "clear" sky. Other choices involving completely sunny conditions or significant cloud coverage also deviate from this accepted measure, reinforcing why the definition tied to less than 1/8th cloud cover is the correct interpretation in meteorological practice.