Where the shape comes from
Read one way as a hard-edged clam or mussel shell once used as a primitive blade for cutting grain, and read another as a star or constellation marking a fixed point in the sky, the two accounts pulling in different directions even in the old sources. Whichever picture is right, the character settled into naming a position in time, the fifth of the twelve earthly branches, and survives today mainly in 星辰, stars, and 生辰, one’s birth date, a person’s own point in the turning sky.
汉字 filed under 辰
No published character on HSK Guide is filed under this radical yet. 汉字库.