What term refers to the event when the upper limb of the sun crosses the visible horizon in the morning?

• A. Sunset
• B. Sunrise
• C. Civil Twilight
• D. Nautical Twilight

Answer: (B)

The event when the upper limb of the sun crosses the visible horizon in the morning is referred to as sunrise. This term specifically denotes the moment when the first light from the sun is visible above the horizon, marking the beginning of the day. Sunrise occurs when the sun's disk is just above the horizon, leading to the gradual increase in daylight.

In contrast, sunset refers to the event in the evening when the sun disappears below the horizon, indicating the end of the day. Civil twilight and nautical twilight are periods of time that occur before sunrise and after sunset, during which the sun is below the horizon but still provides some level of natural light; these terms are related to the specific angles of the sun below the horizon that affect visibility and navigation, but they do not describe the moment when the sun begins to rise.