1990 what is the solar term on September 28th of the lunar calendar?

1September 28th, 990 is not a solar term. September 22nd is the beginning of winter.

* * * Twenty-four solar terms a year:

Beginning of spring, Rain, Creeping, Vernal Equinox, Qingming, Grain Rain, Changxia, Xiaoman, Mangzhong, Summer Solstice, Xiaoshu, Dashu, beginning of autumn, Chushu, Bailu, Autumnal Equinox, Cold Dew, Chufrost, beginning of winter, Light Snow, Heavy Snow, Winter Solstice, Slight Cold and Severe Cold.

A year is 12 months, so it can be said that a solar term is half a month.