Today is Chinese New Year and sees us saying goodbye to the Rat and hello to the Ox. But, while most of us are relatively familiar with the idea of animals marking the 12-year cycle of the Chinese calendar, we probably know less about how this calendar works.

It is a luni-solar calendar, meaning that it is based on the apparent motions of both the Moon and the Sun. Because the lunar months (29.5 days) do not match the solar year (365.25 days), there always several days 'left over'. This problem is solved by adding an extra, intercalary month seven times in every 19 years. The Chinese new year moves around (between 20 January and 19 February) in our calendar because it is timed to coincide with the first new moon after the winter solstice.

The 12 animals assigned to the years reappear elsewhere in Chinese calendars and astronomy. They are used to represent the 12 ordinary months, a cycle of 12 days and even two-hour periods within each 24-hour day. In astronomy, the animals are associated with the stations which Jupiter passes through in one revolution around the Sun (an 11.86-year cycle) and yet another association is with compass directions. Chinese compasses and sundials in the Museum collections therefore include the characters for the animals.

Inclining dial, 1850-1900, by Fang Xiu-Shui

Families will get a chance to have a closer look at instruments like this during half-term (20 February 2008) when I will be displaying and talking about them at the ROG. You can find about more about details of this and other Chinese New Year events at the museum.