The number nine in winter starts from the winter solstice and ends at the Waking of Insects, that is, from December 22 to March 12 of the following year. Every nine days is counted as a period until the end of ninety-nine and eighty-one days.
By analogy, 19 refers to December 22 to December 31, 29 refers to January 1 to January 9 of the following year, and 39 refers to January 10 to 1 On the 19th of the month, 49 refers to January 20th to January 29th.
"Nine Numbers" is a folk solar term in winter in my country, which reflects the general situation of winter temperature changes in China. It vividly records the climate and phenological changes between the winter solstice and the next spring equinox, and also expresses some laws of agricultural activities.
Extended information:
Our country has a vast territory, and the "Nine-Nine Songs" vary from place to place; but they are similar.
1. There is a popular Chinese folk song like this (Beijing version):
One thousand nine hundred and twenty-nine did not take action.
Three-nine-four-nine walking on ice.
Watching willows along the river in 5969.
The river opens in seventy-nine months, and the wild geese come in eighty-nine years.
Nine-nine plus one-nine, the plow oxen are everywhere.
2. Shanxi Datong Edition:
One thousand nine hundred and twenty-nine does not count as nine.
Three nineteen and forty-nine call the dog.
Fifty-nine and sixty-nine open the door and walk away,
Seventy-nine and eighty-nine, the river opens to see the willows,
Nine-nine plus one-nine, the cattle are everywhere.
Baidu Encyclopedia--Dong Jiujiu
Baidu Encyclopedia--Nine Numbers