Nowadays, solar calendar is prevailing all over the world. However, both solar and lunar calendars are coexisting in China. Chinese Lunar calendar, also named Nongli（农历） or Xiali（夏历）, is a calendar whose date indicates the moon phase. This is normally done by having a month which corresponds to a lunation so that the day of month indicates the moon phase. If a calendar tracks the seasons, it is also a lunisolar calendar.

Chinese Lunar Calendar is also lunisolar and most calendar systems used in antiquity. The reason for this is that a year is not evenly divisible by an exact number of lunations, so without any correction the calendar year will drift with respect to the seasons.

Lunar Month: the period of one revolution of the moon, particularly a synodical revolution; but several kinds are distinguished, as the synodical month, or period from one new moon to the next, in mean length 29 d. 12 h. 44 m. 2.87 s.; the nodical month, or time of revolution from one node to the same again, in length 27 d. 5 h. 5 m. 36s.; the sidereal, or time of revolution from a star to the same again, equal to 27 d. 7 h. 43 m. 11.5 s.; the anomalistic, or time of revolution from perigee to perigee again, in length 27 d. 13 h. 18 m. 37.4 s.; and the tropical, or time of passing from any point of the ecliptic to the same again, equal to 27 d. 7 h. 43 m. 4.7s.

Determining the start of the month: In Chinese Lunar Calendar, the first day of the month is determined by determining the day during which the moment of new moon arrives, according to a particular time zone.

The length of a lunar month: The average length of the synodic month is 29.530589 days. This means the length of a month is alternately 29 and 30 days (termed respectively hollow and full).The length of a month is difficult to predict and varies from its average value. Because observations are subject to uncertainty and weather conditions, and astronomical methods are highly complex, there have been attempts to create fixed arithmetical rules. In Chinese Lunar Calendar, the months are adjusted as adjusted in the common or Gregorian calendar; April, June, September, and November, containing 30 days, and the rest 31, except February, which, in common years, has 28, and in leap years 29.

Lunar Day: In space exploration, a lunar day is the period of time it takes for the Moon to complete one full rotation on its axis with respect to the Sun. Equivalently, it is the time it takes the Moon to make one complete orbit around the Earth and come back to the same phase. It is marked from a New Moon to the next New Moon.