The date of september 22 or 23 is the
a. autumnal equinox.
b. winter solstice.
c. summer equinox.
d. autumnal solstice.

A. autumnal equinox.

Explanation:

- The equinox is defined as the moment of the year when the Earth's axis is perpendicular to the direction of the sun's rays. When this occurs, the day and the night have the same length (12 hours) at every point on the Earth's surface. The equinox occurs twice per year:

++ March 20-21: this is called spring equinox, since it marks the beginning of spring

++ September 22-23: this is called autumnal equinox, since it marks the beginning of autumn

- The solstice is defined as the moment of the year when the angle between the direction of the Earth's axis and the direction of the sun's rays is maximum. This occurs twice per year:

++ June 20-21: this is called summer solstice. On this day, the lenght of daylight is maximum in the northern emisphere, while it is minimum in the southern emisphere

++ December 21-22: this is called winter solstice. On this day, the length of daylight is minimum in the northern emisphere, while it is maximum in the southern emisphere