A set of high-definition, watermark-free mobile wallpapers of the autumnal equinox to share with everyone. The autumnal equinox is the sixteenth of the twenty-four solar terms and the fourth solar term of autumn.Dou Zhiji; the sun reaches 180° of the yellow longitude; the festival is held on September 22-24 every year in the Gregorian calendar.On the autumnal equinox, the sun shines almost directly at the Earth's equator, making days and nights the same length all over the world.