Why do Chinese celebrate animals in the year?

There are twelve animals in the Chinese Zodiac. The origins of the Chinese Zodiac are not known, but there are many legends. The legend that I know of is that there was a race held by the Jade Emperor and the first twelve animals to finish would win. As the race went on various things happened and the animals that won were as follows: rat, ox, tiger, rabbit, dragon, snake, horse, goat, monkey, rooster, dog, and pig. There are many other legends and nobody knows for sure why these were the twelve animals.

It gets a bit more complex, the animals in the cycle are tempered by the five Chinese elements of Metal, Water, Wood, Fire and Earth. This means you have (for example) fire pigs, water rats etc.