Contrary to what you might expect, the Chinese calendar isn’t a lunar calendar. Instead it’s lunisolar—meaning that it’s based on measurements of the phases of the moon, but also on the position of the sun in the sky. Instead of following the solar calendar in having one leap day every four years, the Chinese calendar introduces a leap month every three years instead. Sounds odd? It’s not that unusual. The ancient Babylonians, Greeks and Jews all used a variant of this calendar. There’s been a lunisolar calendar in China since at least the Shang Dynasty, around the 14th century BC. Actually, legend holds that the semi-mythical Yellow Emperor invented the calendar in around 2500 BC—but he’s also said to have invented math, agriculture, boats and football, so you can take this with a pinch of salt. In ancient China the secrets of the calendar were jealously guarded, the purview of the king or emperor himself. After all, the emperor carried the mandate of heaven upon his shoulders, which is what allowed him to rule. The interpretation of the spheres was naturally his to pass down. The royal astronomers made their calculations to draw up the calendar, predicting eclipses and forecasting the future. More to the point, it would also be used to tell the people when they should be planting crops or harvesting them. The brand new Republic of China adopted the Western Gregorian calendar on January 1, 1912, as an attempt to break away from the authority of the emperor. After all, if you’ve quashed his divine mandate of heaven, then he no longer has control over the months or days of the week. Since then, China’s been officially run on the solar calendar. What are the benefits of a lunisolar calendar? Well, aside from easily being able to tell the phases of the moon and tidal patterns, there aren’t that many. They don’t allow you to pinpoint where the Earth is in relation to the sun and more practically, it’s harder to align the months exactly with the seasons. But we still use the lunar calendar to mark festivals and decide on auspicious periods for weddings, funerals and more. After all: Who wants to mess with the divine mandate of heaven?