Anniversary Dates
Hermetic Systems

An Asian Lunar Calendar Date Conversion Tool

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a user license
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This software concerns dates in five different calendars: the Chinese Lunar Calendar, the Vietnamese Lunar Calendar, the Japanese Lunar Calendar, the Gregorian Calendar (a.k.a. the Common Era Calendar) and the Archetypes Calendar. The Asian calendars differ mainly in the degree of longitude used as the prime meridian (a.k.a. the reference longitude): 105° East for Vietnam, 120° East for China and 135° East for Japan (which is the same as that for the Korean Lunar Calendar). The Archetypes Calendar is included because it has an interesting relation to the Chinese Calendar, as explained here.

The simplest use of this software is to find the Gregorian and Chinese dates for today, which is done simply by clicking on the Today button:

The next-simplest use is to find the Chinese date corresponding to your Gregorian birth date. For example, if you were born on 1980-02-20 (February 20, 1980 CE) then the following settings and results shows that your Chinese birth date is the 5th day of the 1st month in a metal-monkey year.

Compatible with Windows 7 An anniversary date with respect to a date in a calendar is a date in the same calendar which has the same month and day number but possibly a different year number, e.g., 2018-12-01 is an anniversary date of 2006-12-01 in the Gregorian Calendar, and the 5th day of the 7th month in the most recent wood-sheep year in the Chinese Lunar Calendar is an anniversary date of the 5th day of the 7th month in the most recent fire-pig year.

All new year's days in any calendar are anniversaries of each other, and this software can be used to get the dates of Chinese lunar new year over any range of Gregorian years, as shown in the settings and results in this screenshot:

Since every Chinese year has a day 1 in month 1, the way in which the Chinese year is specified for this problem is irrelevant; any year will get the same result for any range of Gregorian years.

The primary problem which this software solves is: Given a birth date (or some other kind of date) in the Gregorian Calendar, find the corresponding date in the Chinese (or Vietnamese or Japanese) Lunar Calendar, then for a given year (or over a given range of years) in the Gregorian Calendar find the dates in the Gregorian Calendar corresponding to the anniversaries of the Chinese birth date.

Here is a screenshot which shows a solution to this problem when the birth date is February 2, 1959:

The birth date given is February 7, 1959, which corresponds to the 30th day of the 12th month in the year 4656 according to the Overseas Chinese way of numbering years, this being an earth-dog year. Thus the anniversaries of this birth date (that is, the subsequent birthdays) are also the 30th day of the 12th month in subsequent years in the Chinese Calendar. For each year in the range of Gregorian years 2004-2010 the software calculates the Gregorian date corresponding to the 30th day of the 12th month in that year. However no result is given for Gregorian year 2006. That's because in the corresponding Chinese year (4703) the 12th month had only 29 days, so there was no 30th day of the 12th month in that year.

However, if the Include missing day 30s checkbox is checked then the software will display the year with the missing 30th day, and the day preceding it, as shown below:

2006-01-28 CE = 4703-12-29 ARC = 4703-12-29 CHL (in a wood-rooster year)

Chinese/Vietnamese/Japanese Anniversary Dates screenshot

This software can also be used to find anniversary dates in the Vietnamese and the Japanese lunar calendars. As noted above, the difference among the three calendars is mainly the degree of longitude used as the prime meridian (a.k.a. the reference longitude). There are also some differences in the animal names (e.g. in the Japanese Calendar "boar" replaces the Chinese "pig", and in the Vietnamese Calendar "cat" replaces the Chinese "rabbit").

After selecting "Japan" for the reference longitude, and after clicking on the Show me button, with the same settings as above, we obtain:


The resulting anniversary dates are the same, the only difference is that "fire-boar year" replaces "fire-pig year".

Note that neither the Japanese Calendar nor the Vietnamese Calendar use the sequential year numbering in use among overseas Chinese. However, this system of numbering years is retained for ease of computation when dates in the Vietnamese and Japanese lunar calendars are displayed.

When switching to the Vietnamese calendar, with the same settings as above, we get a slightly different result:


Instead of (as in the Chinese calendar)

2007-02-17 CE = 4705-01-01 ARC = 4704-12-30 CHL (in a fire-dog year)

we get

2007-02-16 CE = 4704-13-30 ARC = 4704-12-29 VNL (in a fire-dog year)

That's because the Vietnamese year correspondng to the Gregorian year 2006-2007 differed from the Chinese year. The 12th month of the Chinese fire-dog year had 30 days but the 12th month of the Vietnamese fire-dog year had only 29 days. (The exact reason for this can be ascertained by an advanced use of the Chinese Calendrics software.)

The problem considered above, namely, of finding anniversary dates in the Chinese Calendar corresponding to a given birth date in the Gregorian Calendar, can be generalized as follows: Given a date (a birth date or some other date) in one of the supported calendars (Gregorian, Archetypes or Chinese/Vietnamese/Japanese), say, Calendar X, find the corresponding date, Date D, in another calendar, say, Calendar Y; then for a given range of years in some calendar Z, find the anniversary dates in Calendar Y of Date D expressed as dates in Calendar Z.

For example, the following screenshot shows the anniversary dates in the Gregorian Calendar (Calendar Y), for the years 4702-4707 in the Archetypes Calendar (Calendar Z), of the day whose Chinese date (Calendar X) is day 5 of the intercalary month 9 of the year nearest to the Gregorian year 2012:

As the preceding example shows, this software supports the specification of dates in any of the three lunar calendars by reference to an element-animal year, e.g., an earth-monkey year (the most recent of which was 1968 CE). The element-animal pairs form a 60-year cycle, and a particular element-animal year re-occurs every 60 years, so a given element-animal pair does not uniquely specify a year. A unique specification is possible by stating the nearest Gregorian year. So "the wood-horse year nearest to 2012 CE" specifies the year 2014 CE.

Suppose that a man knows that he was born on the 30th day of the 12th month of the Chinese Calendar in an earth-dog year, but he does not know exactly which year that was in the Gregorian Calendar. But he knows he is about 50 years old (in 2011 CE), which implies that his year of birth was approximately 1961 CE. We can get his Chinese birthdays over the period 2009-2015 in the Gregorian Calendar with the settings (and results) below:

Note that, because the Including missing day 30s checkbox was checked, the results include day 29s in Chinese years 4709 and 4710 because in those years the 12th month had only 29 days not 30.

Suppose now that a man knows that he was born in a metal-snake year in the Chinese Calendar, and on January 19 in the Gregorian Calendar, but he does not know exactly which year that was in the Gregorian Calendar. But he knows he is about 70 years old (in 2011 CE), which implies that his year of birth was approximately 1941 CE. The following settings and results ...

... tell us that the metal-snake year nearest to 1941 CE ran from 1941-01-27 through 1942-02-14. Since he was born on January 19, the Gregorian year of his birth was 1942. We can thus adjust the settings as follows to get the desired results:

Thus his Chinese birthday (the 3rd day of the 12th Chinese month) occurs occurs twice in the Gregorian year 2011 but does not occur at all in the Gregorian year 2012. That's because 2011 CE runs from day 27 of month 11 (in 4708 CHL) through day 7 in month 12 (in 4709 CHL) — as we see from the results below — so it contains two days 3 of month 12. And 2012 CE runs from day 8 of month 12 (in 4709 CHL) through day 20 of month 11 (in 4710 CHL) so it does not contain a day 3 of month 12.

Anniversaries of dates in the Chinese calendar where the month is an intercalary month are given in the intercalary month when the year has the corresponding intercalary month and in the corresponding non-intercalary month when it doesn't. This is made clear by the following example. Suppose a man knows he was born on day 29 of (intercalary) month 2* in a fire-pig year somewhere around 1950 CE, and wants to know what his birthdays (as dates in the Gregorian Calendar) were for the years 2002 through 2006. The software tells us:

The Chinese year corresponding to 2006 CE (namely, 4704) has an intercalary month 7*, but no Chinese year in the years 2002-2006 CE has an intercalary month 2* except for the Chinese year corresponding to 2004 CE.

As a final example, suppose a man knows he was born on day 30 of (intercalary) month 6* in a metal-snake year somewhere around 1940 CE, and wants to know what his birthdays (as dates in the Gregorian Calendar) will be for the years 2016 through 2018. The software tells us:

Chinese years 4714 and 4716 do not have an intercalary month 6*, so the anniversary in these years is in month 6. Month 6 in year 4716 has only 29 days, so the anniversary date is 4716-06-29 CHL.

On initial startup there are no selections shown for calendars, years, etc. Clicking on the Use default settings button will set things up for a typical request, which you can then modify as desired.

The Save settings button will save the current selections so that they are reloaded when restarting the program.

The Copy to clipboard button can be used to copy the results in the output text box to the clipboard, from which they can be pasted (using 'ctrl-V' or a copy command) into some other program.

The Reset button can be used if it ever happens that on program startup the settings are garbled. Reset removes all settings and starts the program as if it were the first time it is being run.

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How to obtain the software: A trial version of Chinese/Vietnamese/Japanese Anniversary Dates is available for free download from this website. Click on the link below for further information:

Download Chinese/Vietnamese/Japanese Anniversary Dates ...

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A single-user license is available for a period of 3 months or 1 year. Prices for each type of license are given at Purchase a User License. An activation key is required in order to make the trial version permanently fully functional, and can be obtained immediately (or soon after) your purchase.

Refund: A refund will be provided promptly up to 30 days after purchase if the software does not perform satisfactorily.

Updates: Purchasers of a user license for this software are entitled to an update to any later version at no additional cost.

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