Which phenomenon occurs when the Sun crosses the plane of Earth's equator?

a. equinox

b. solstice

c. summer

d. winter

The phenomenon that occurs when the Sun crosses the plane of Earth's equator is equinox. An equinox is commonly regarded as the moment the plane of Earth's equator passes through the center of the Sun's disk, which occurs twice each year, around 20 March and 22-23 September.

Answer;

Equinox

Explanation; Equinox commonly refers to the instant of time when the plane of Earth's equator passes through the center of the Sun which occurs twice each year: around 20 March and 23 September. During equinox, the Earth's axis is tilted neither toward nor away from the sun, resulting in an almost equal amount of daylight and darkness at all latitudes.