This paper will provide a brief, selective outline of the concept, the calendar, and the historical, philosophical and mythic setting of festivals in early imperial China aimed to highlight the interplay between exact science and political ideology in fixing the rhythm of public religious life. In short, the ancient Chinese had festivals, which were framed in terms of the particular sacrifice, rite or ceremony at their centre, and it is under the Han Empire (206 BCE–220 CE) that we begin to get a detailed historical view of an ensemble. This ensemble predates the major religions of later Chinese history – Buddhism, Taoism, etc. – and it would continue to evolve to structure public life after their advent. Whatever the actual origins or regional differences in festivals, the imperial state and Confucian intellectual class placed their idealised forms alongside such events as heliacal risings, the thawing of the soil, and the return of various plants and animals in a totalistic vision of natural order as the dynamic cosmic harmony between ‘all the ten thousand things’ of creation over their respective seasonal cycles. In other words, the rites not only mark and act out natural cycles, they actively maintain them: humanity is a symphony orchestra, conducted by the Son of Heaven, every member of which must play in tune and rhythm with one another and with the birds and bees, the mountains, oceans and stars, or else drown the universe in cacophony. It was the state that fixed the festival calendar every year, and with this context in mind, we will look at some of the more absurd demands that this ideology placed on the state Astronomical Bureau to ‘get it right’.