Spring Equinox: March 21st; Summer Solstice: June 21st; Autumn Equinox: September 22nd; Winter Solstice: December 21st.

The equinox is the day when the sun shines directly on the Earth's equator, and the seasons are reversed in the northern and southern hemispheres; the northern hemisphere is the spring equinox, and in the southern hemisphere it's the fall equinox.

Summer solstice on this day, the position of the sun directly above the ground to reach the northernmost point of the year, almost directly to the Tropic of Cancer, at this time, the northern hemisphere's day up to the longest, and the further north the longer

Autumn equinox, the climate of the south by this festival from the beginning of the beginning of autumn. The sun reaches 180 degrees of yellow longitude on this day and shines directly on the Earth's equator, so the 24-hour day and night on this day are equally divided into 12 hours each; there is no global extreme day and night phenomenon.

The winter solstice, the bucket refers to the son, the sun's yellow longitude reaches 270 °, in the annual calendar December 21-23 cross section. The winter solstice marks the minimum solar altitude and the shortest day in the northern hemisphere.