You may have noticed that Chinese solar months start at some point between the fourth and eighth day of a Western month. For instance, the ninth solar month of the Chinese calendar (the Month of the Dog) starts on October 8 and runs until November 6. This is dictated by the use of the 24 solar terms or jie chi in fung shui calculations. The 12 jie mark the beginning of a month and the 12 chi mark the midpoints.
Solar terms are used to indicate climatic and agricultural conditions, important to agrarian communities in days gone by. The first solar term, the beginning of spring or Li Chun, which mostly falls on February 4, marks the beginning of the solar year. The festival of Ching Ming is identified by the fifth solar term and usually falls on April 5. The midpoints of the months coincide with Western benchmarks - the spring equinox or Chiu Fen (fourth solar term) was on March 20 this year and the winter solstice or Dong Zhi (the end of winter) will be on December 22.
The 24 solar markers are used by fung shui masters to help schedule festivals and occasions such as burials. They are also present on luo pan (fung shui compasses).