What is the condition under which Celestial Navigation can be conducted?

Celestial navigation can be conducted both during the day and at night. The key reason for this is that celestial bodies, such as the sun, moon, and stars, provide navigational reference points regardless of the time of day. During the day, although the visibility of stars may be hindered by sunlight, the sun itself serves as a crucial celestial body for navigation. Techniques such as measuring the sun's altitude or using it to determine your position can be performed effectively during daylight hours.

At night, stars and other celestial objects become visible, allowing for traditional celestial navigation methods to be used. Navigators utilize instruments such as sextants to measure angles between celestial bodies and the horizon, leading to accurate positional information.

Other conditions mentioned in the choices, like clear weather or civil twilight, may enhance the process or visibility of celestial bodies but are not absolute prerequisites for celestial navigation to occur. The practice remains effective under varying conditions, making the option of conducting navigation both day and night the most encompassing and accurate.