There are 24 seasonal points annually.

12 of which marks the commencement of each solar month (jie), with the remaining 12 marking the mid-months (qi). Which leads to the name 24 jie qi (二十四节气).

For example, the first day of the first lunar month begins on li chun (立春), with it’s mid-month on yu shui (雨水).

Season Lunar
Spring 1 E3 立春 (li chun)
雨水 (yu shui)
Feb 4,5
Feb 18,19
Spring 2 E4 惊蛰 (jing zhe)
春风 (chun feng)
Mar4 5,6
Mar 20,21
Spring 3 E5 清明 (qing ming)
谷雨 (gu yu)
Apr 4,5
Apr 20,21
Summer 4 E6 立夏 (li xia)
小满 (xiao man)
May 5,6
May 21,22
Summer 5 E7 芒种 (mang zhong)
夏至 (xia zhi)
Jun 5,6
Jun 21,22
Summer 6 E8 小署 (xiao shu)
大署 (da shu)
Jul 7,8
Jul 22,23
Summer 7 E9 立秋 (li qiu)
外署 (wai shu)
Aug 7,8
Aug 23,24
Summer 8 E10 白露 (bai lu)
秋分 (qiu fen)
Sep 7,8
Sep 23,24
Summer 9 E11 寒露 (han lu)
霜降 (shuang jiang)
Oct 8,9
Oct 23,24
Summer 10 E12 立冬 (li dong)
小雪 (xiao xue)
Nov 7,8
Nov 22,23
Summer 11 E1 大雪 (da xue)
冬至 (dong zhi)
Dec 7,8
Dec 21,22
Summer 12 E2 小寒 (xiao han)
大寒 (da han)
Jan 5,6
Jan 20,21

Legend of earthly branches can be found here.

The above table of the 24 sub-seasons is usually used in bazi analysis to go deeper into the characters.