Many Chinese Almanac information is determined by the Chinese Lunar Calendar. For example, the first day of the Lunar month is not an auspicious day for wedding. Because the first day of the lunar month is the new moon day and  the new moon days might be on different days among different time zones, therefore the lunar calendar for each time zone might be different.

For example, the first day of 8th Chinese Lunar is different from China and USA in 1999.

This causes the date of Chinese Moon Festival is on 9/23/99 in USA and 9/24/99 in China, because the date of Chinese Moon Festival (a.k.a. Mid-Autumn Festival) is on the 15th moon day of 8th Chinese Lunar month.

The worst case for the discrepancy is the Lunar Leap month (extra lunar month). Because the first day of the lunar month might be on different day, then the Lunar Leap Month might be assigned to different month. That means the almanac information might be completly different for several months after the Lunar Leap Months.

Before looking for the moon astronomical data, we need to know more about the Lunar Leap month. 

There are two types of Chinese Calendars. One is the Chinese Civil Calendar, which is posted by the Chinese government. The other is the Chinese Astronomical Calendar, which is used by astronomers. The basic rules for both these Chinese Calendars are

• The new moon day is the first day of a lunar month
• The name of a lunar name is named by the Solar Center Point
• The lunar month without a Center Point is a Leap month

The major difference between the Chinese Civil Calendar and the Chinese Astronomical Calendar is the assignment of leap months.

If the new moon day and the Solar Center Point are on the same day, the lunar month contains that Solar Center Point in the Civil Calendar system. In the Astronomical Calendar, we have to compare the new moon time and the Solar Center Point time (hour, minute and second). The lunar month contains that Solar Center Point only if the Solar Center Point time comes after new moon time.

In short, the Astronomical Calendar is much more accurate than the Civil Calendar. 

There is a leap month in the Chinese Calendar year 2001. The following is the listing of leap months for Chinese Calendar year 2001 in China, PST and EST time zones. We can see the leap months in the Astronomical Calendar side are consistent, but not in the Civil Calendar side. 

The books of Chinese Farmer's Almanac in the bookstores are using the China Civil Calendar, which is East longitude 120 degree. That's why the Chinese Farmer's Calendar software might generate more difference from the books of Chinese Farmer's Almanac when comparing non-China time zone.

China Beijing/Taiwan Standard Time - Longitude East 120th degree - click here for explanation

Pacific Standard Time (PST) - USA Longitude West 120th degree - click here for explanation

Eastern Standard Time (EST) - USA Longitude West 75th degree - click here for explanation

The information of Chinese Farmer's Almanac are from the Chinese lunar/solar calendars, Five Elements, I-Ching, Purple White Flying Star, Feng Shui theory, Yin Yang, Astrology, Astronomy, Five Stars/Nine Stars Astrology, Weather statistics, Oracle, Religion, 12 Cycle Days, 28 Stars, 6 Animal Days, 72 seasons, Funeral theory and so on.

The first Chinese calendar was made in the Xia Dynasty around 2,205 B.C. In the early Qin Dynasty around 246 B.C., the almanac information was beginning to develop. In the later Han Dynasty around 25 A.D., there were many almanac theories to confuse people in the society. An emperor announced to follow the Five Element theory when a conflict was started among theories. The Chinese farmer's almanac matured around Song Dynasty around 960 A.D. 

There are many different almanac schools since thousand years ago. Different schools use different factors to determine a lucky or bad day for a special event. As a result, a lucky day from one school might be an unlucky day from another school. 

The logic for Chinese Farmer's Calendar software to determine a lucky day or bad day is from more than 10 Chinese advanced Almanac books. It uses the hints of Five Elements, 24 solar seasons, 12 cycle days, 28 stars and special almanac days and factors to calculate the almanac information. The software should be found some difference from the Chinese Farmer's Almanac books.

Actually, any two Chinese Farmer's Almanac books should have some difference as well. If there are two books that are identical, then one is a copy of another.

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