The Chinese zodiac is a classification scheme based on the lunar calendar that assigns an animal and its reputed attributes to each year in a repeating 12-year cycle. The 12 year cycle is an approximation to the 11.85-year orbital period of Jupiter.
Many people have wondered over the years how it was that the Rat, the
smallest of all the creatures, was given the honour of having the first year
of the Chinese Zodiac named after him. This is the story I have heard.
A very long time ago, the Jade Emperor, who ruled the heavens of China,
sent a message to all the animals asking them to come together so that
he could give each of them a year, which would make it easier for the
people of China to keep track of time. The Cat and the Rat were good
friends and decided to travel to meet the Jade Emperor together.
When it came time to leave, however, the Cat was taking a nap. The Rat, realising that he would have to use all his cunning to be noticed by the Jade Emperor, left his friend sleeping, and set off on his own. This is why there is no year named after the Cat, and also why Cats have hated Rats even since.
When the Rat arrived, the Jade Emperor welcome him and the other animals and told them that they should all take part in a swimming race. Once again, the rat realised that he would have to be very clever if he wanted to win the race. He found the largest, strongest animal, which was the Ox, and pleaded with him to let him ride on its head. The Ox was kind and strong, and agreed that they would swim across together. The Rat travelled safely across the river on the Ox’s back, but, just before they reached the other side, climbed over the Ox’s head, jumped onto land, and reached the finish line first. The Rat had proved its cunning, and the Jade Emperor named the first year after the Rat and the second year after the Ox.