Every year Chinese New Years happens on a different day according to the Western Calendar. For the most part it falls somewhere between January and February. But why is that?

The Chinese calendar is based on the lunisolar calendar, which takes into account both the phases of the moon and the season. Each new moon represents the start of a new month. However, if we simply used the moon, the calendar would soon be inaccurate in telling the correct seasons and time of the year. Thus, the calendar also accounts for the position of the sun in the sky. The sun's longitude starts at 0 during the vernal equinox and completes a full circle through the year. The first month occurs when the sun's longitude is at 330 degrees, approximately two full moon cycles after the Winter Solstice, which occurs in the later part of December.

Since a full year is 365.24 days, every few years there is an extra month in the lunisolar calendar and thus the year is known as a Leap Year. There are a few ways to determine if the year is a leap year. One way is to count how many new moons occur between Winter Solstice, which must always occur in the 11th month for the calendar to work.

Our current International/Western calendar is based on the Gregorian calendar. It is actually not the first calendar used in the Western world, but rather an modification to its predecessor, the Julian calendar. Since a full year is still not ending on a full day, we have in the Western World "leap days" and "leap seconds" occurring to account of the lost time.

Interestingly enough, because of this difference in what day New Years actually falls, in order to obtain your Chinese zodiac you actually have to recalculate your Gregorian birthday based on the lunisolar calendar.

Don't know how to do this? Well don't fret too much, there are many handy sites, like this conversion tool, that can do it for you. Just enter the year, month and date of your birthday and hit "Convert". The first line will show you your birthday date formatted as year.month.date. The second line will show you your birthday as it should be in the Chinese calendar formatted as year.month.date. And to the right of that will be your Chinese Zodiac.

Many cultures aside from the Chinese have used this calendar system to measure the passage of time. Among the noteable ones are Hebrew, Tibetan, and some Hindu calendars.