Which of the following events marks the time when day and night are of equal length?

The time when day and night are of equal length is marked by the Vernal Equinox. During this event, typically occurring around March 21st, the tilt of the Earth's axis is such that the Sun is positioned directly above the equator. As a result, nearly all locations on Earth experience approximately 12 hours of daylight and 12 hours of nighttime.

In contrast, the Winter Solstice, which occurs around December 21st, is the shortest day of the year, and the Summer Solstice around June 21st is the longest day. Equatorial Sunset refers to the specific time of day when the Sun sets at the equator, but it does not correspond to a global balance of daylight and darkness. Thus, the Vernal Equinox is uniquely significant as it symbolizes the transition towards longer days following winter, making the equal division of day and night a key characteristic of this equinox.