The Lunar New Year is determined by cycles of the moon and therefore the dates are movable, each new year commencing on the new moon which occurred in the late January or February of the Western Calendar. It is not the Chinese New Year but the Lunar New Year as the date is celebrated by many others besides the Chinese.
A Chinese proverb states that all creations are reborn on New Year's day. The Chinese New Year is a celebration of change ... out with the old and in with the new! The Chinese New Year falls on a different date each year because it is based on a combination of lunar and solar movements.