What does the old saying weather 39 49 mean?

Walking on the ice in 3949,

Look at the willows in 5969,

79 rivers opened and 89 geese came.

99 plus 19,

Cows are plowing the fields everywhere.

It means the phenology of "Winter Nine" days. September 19 and September 29 were too cold to raise their hands; It is colder in March and April, and the ice is thick enough for pedestrians to pass; It began to pick up on May 9 and June 9, and the distant willows are now spring; The ice of the 79 River began to melt; 89 Nanyan flies back; Spring ploughing began after the Ninth Five-Year Plan. Note: The winter solstice is the first day of the ninth National Day every year, and nine days is a ninth National Day, which is ***8 1 day. Because the winter solstice is basically on February 22nd of 10 every year, the date of "Jiujiu" is basically fixed.