The Google logo on many of the Google home pages is to celebrate the Lunar New Year. It is the first day of a secular, sacred or other year whose months are coordinated by the cycles of the moon. It is also the Chinese New Year.
The Google Doodle, displayed below, shows a ram or maybe a sheep or maybe a goat slamming into a tree setting off a set of chain reactions leading to a fireworks display.
Depending on where you are, you may get a different logo, like in various Asian countries.
The Google UK team said on Google+:
Lunar New Year celebrations...Sheep, ram, or goat? Whatever the animal, celebrate the Lunar New Year with our special #GoogleDoodle .
Find photographs, blogs and videos from around the world - and share your own - by clicking on the #CNY hashtag.
You can see a higher resolution version of this Doodle over here. Here is the Vietnam version,
Forum discussion at Google+ and Google Web Search Help.