Lidong (also known as Rittō, Ipdong, or Lập đông) is the 19th solar term in the traditional Chinese calendar. It marks a specific period within the annual cycle based on the position of the Sun relative to the celestial longitude.
The term begins when the Sun reaches the celestial longitude of 225° and concludes when it reaches 240°. While it refers to this duration, it most commonly identifies the specific day the Sun is positioned at exactly 225° celestial longitude. In the Gregorian calendar, Lidong typically occurs between November 7 and November 22.