CAL20000 진짜萬歲曆 USER GUIDE

This calendar is made based on the calcuation of accurate sun and moon position. The effective year range is from -10000 to 10000.
This calendar display a month which is just only Gregorian calendar in total effective year.(Julian calendar date do not be displayed in this calendar).
On the month table, Each day cell have solar day number which is Gregroian date, lunar month/day number , sexagenary day unit(日辰 or 干支), star letter of 28 mansions(二十八宿). These data of a day have been used very long period which is maybe from more than 5000 years ago to now and currently is used widely in Korean and Chinese real life.
And also it is indicated the 24 solar terms, new/full moon time with eclipse occurance and it's floating Julian day number for verification of accuracy.

You can download this program or view web page by making selection on the left menu.

V0.91 : Initial Version 1998

V0.92 : 1998.November 5
- 24 solor term calcuation speed and algorithm is improved. Error range of 24 solor term is also improved from 2 hour to 20 minute.
- Solor Eclipse occurrence is added.

V0.93 : 1999.september.11
- Extended effective year range : Year range is from -2085~6077 to -10000~10000. This is done by using 64bit integer value on the Delphi tool.
From year -10000 to now, the speed of calculation is almost same, but present to year +10000, the speed is slower as much as year number is larger.
- Full Moon time is added
Full moon time & lunar eclipse occurrence is added.

V0.94 : 2000.November.8
Added Julian Day number(floating) indicate to day information window

V0.95 : 2008.December.18
24 Solor term time, New/Full moon time is also indicated Julian day number.
Julian Day number 1.00 mean UTC+0(=noon 12:00), Korean Time of 1.00 is 21:00.

V1.00 : 2011.August
Android Version is released. The detailed information for Android/Smart Phone version is on here.

* Please be aware of that the day information on this calendar and historic calendar can be difference because of many reason. This calendar just make calcuation and show only based on the material of present astronomy and physics. But calcuation value can have some error range and be difference to the true value. And historic data was determined based on the material of the past. As the present value is more close to true value than the past value, but the past day was determined at the past time and the day information can not be changed now.
Please make sure the difference of the lunar first day and lunar intercalary month(閏月) between the past and the present caused by calcuation method and error range.
The more detailed information about this is described below.

* There is no year 0 in historic calendar. People use year BC 1 instead of year 0. the previous year of year 1(=AD 1) is BC 1. However, there is year 0 in this calendar because it use scientific numbering system. If you want to see year BC 5, you shall use year -4. And So on.

* The display method of this calendar is just only the Gregorian calendar. If you want to know Julian calendar date, you have to adjust below value to day which is difference between Julian and Gregorian.

After March AD 4       -2 day       After March AD 900 5 day
After March AD 100    -1 day       After March AD 1000 6 day
After March AD 200    0 day       After March AD 1100 7 day
After March AD 300    1 day       After March AD 1300 8 day
After March AD 500    2 day       After March AD 1400 9 day
After March AD 600    3 day       After March AD 1500 10 day
After March AD 700    4 day       After March AD 1583 It was changed to Gregorian date

Befor AD 4, The historic date is not compatible to Julian calendar because the date was controled by the Roman Emperor's own will. However, The Western use the uniform Julian calendar for astronomic purpose. So you are also needed to adjust -1 day for every 100 year for before AD 4.

* Lunar first day error

The lunar first day of a month is determined by the exact time of new moon. If the time is around the midnight, It is very difficult to determine which day is the first day. For example, if the time of new moon is 23:59, the day of before midnight is lunar first day, and if the time is 00:00, the day of after midnight is lunar first day. Just one minute difference make one day difference. At present, as we can calculate and estimate a future new moon time with very high accurate, but it is not enough accruate to make determine a right lunar first day. (Furure, If someone make more accurate equation than present, the new moon time will can be changed and lunar first day also will can be changed)
So, Future lunar first day far from now shall be determined at that time of future.
However, the past lunar first day was determined at the past, It can not be fixed at now. You have to know about this error and use this calendar very carefully when a new moon time is around midnight. When It is differ between historic date and this calendar date for a lunar first day, Cal20000 can be wrong or right with in error range. please refer below error range.
If it happens, the lunar month date will be shift a day all in the month, but the previous month and the next month date are normal date.
And lunar day shift could be happen by difference time zone. the longitude difference of Seoul and Beijing is around 7 degree and this make around 30 minute time difference. So, It happen rarely in historic record when new moon time is around midnight.

* Lunar intercalary month error

Lunar intercalary month is determined by the exact time of new moon and the exact time of mid term of the 24 solar term. So, it is also applyed lunar first day error to the same 24 solor term error and to determine a intercalary month. This error make that a intercalary month move with in 3 month front or rear to real intercalary month. If there is a intercalary month of a specific year on CAL20000, there must be exist the intercalary month on historic calendar with in 3 month. It is very useful to use with sexagenary day number(日辰) for confirm a lunar date or intercalary month.
A lunar first day and a lunar intercalary month can be moved by the method of moon/sun position calcuation as average(平朔/平氣) or real value(正朔/正氣).
As reference, because the value of sun/moon position calculated by CAL20000 is very precise, the historic lunar date can be difference one day to CAL20000 date and the historic intercalary month can be difference within 3 month front or rear.

The epoch of the calcuation for the 24 solar term is 22:08 Feb 4, 1996(丙子年 立春) and a tropical year length is 365.2423611 days(=365 day 5hour 49min=525949 mininute)
The epoch of the calcuation for moon position is 00:00 Dec 31, 1995.
A tropical year length is about 15 second larger than the real value. If you have any question or opinion, please mail to me about this.

The 24 solor terms are calculated by my own method.(Strictly speaking, I follow traditional calcuation method of Korean/Chinese calendar).

The new/full moon time are calculated according as the sun table equation of Newcomb's and the moon table equation of Brown's which are based on theory of the present astronomy with my own algorithm. You can see the initial my own algorithm from the Delphi & Perl source on the left menu.

The Gregorian Calendar have one day error for 3300 years, CAL20000 have almost no error.

The precise error range is here.
The error range for 24 solar term - max 20 minute, average 10 minute, standard deviation 5 minute
The error range for new moon - max 40 minute, average 20 minute, standard deviation 10 minute
This error range is estmate value but it is almost real value I think.

New moon day and 24 solor term day is changed when it is around midnight(When is 23:59 and 00:00). This make the shift of lunar month day and intercalary month.

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Above Error Range was estmated when I made cal20000 first, mid 1998. And there was no referene to be compared to at that time.

At that time(1998), I thought that above error range was applied to all effective year(-10000~10000).

At present(mid 2011), I have a reference to campare CAL20000 value with. It is NASA eclipse site data.

The solor eclipse exact time which was occurced Julian day 991085 (CAL20000 - Gregroian date -1999.5.25, NASA Eclipse site - Julina Date is -1999.July.12), is that the JD number of NASA is 991085.63500, and the JD nubmer of CAL20000 is 991085.482638889. The difference is 0.152361111 day(=991085.63500-991085.482638889), this is about 219 minutes equal to 3 hours 40min.

There is 3hour 40min error on moon posion for 5000 year ago between NASA value and CAL20000 value.
Solor term error is around 1.2~1.4 day for 5000 year ago(year -1999) between CAL20000 value and the value which is based on theory of the present astronomy.

I have confidence with evidence data which are based on Korean/Chinese historic record that my calcuation result is far more close to real value than the value from the theory of the present astronomy.

- A lunar month name and intercalary month problem when is occured a lunar month include two mid term around the perihelion is corrected by resonable method.

- The reference books are the principle of calendars(曆法의 原理分析 written by EunSung Lee, Korean book), Almanacs(1988, 1990 1992, 1993, 1996, 1997,1998) printed by the Korea Astronomy and space science institute.
The calcuation value are verified with Sun-node lunisolor(日交陰陽曆, 1983, editted by EunSung Lee, Korean book), Korean history annals(BC 57~AD 935) for three nation(三國史記), Spring and Autumn Annals(春秋, Written by Confucius), Records of the Grand Historian(史記, witten by Sima Qian)

- The solor eclipse records on Spring and Autumn Annals(春秋) and Korean history annals for three nation(三國史記) are meet to the value of CAL20000. You also can see these eclipse on the historic records at CAL20000 as you check with sexagenary day number(日辰) which are on the historic records. Also the solor eclipse which was predicted but could not see at Korea on korean historic record had been occured at south america.

- The information about this CAL20000 program or lunar calendar are on my hompage http://user.chollian.net/~kohyc/calendar and my email address is kohyc@chol.com (Please mail to me with Korean or English only, I don't know other language and I am not good at English)

- It is very helpful to let me know if CAL20000 program has any error.

- USAGE

Just enter Year(-10000~10000) and month(1~12). then the information for the month will be displayed. The information values are only Gregorian date value.

- Displayed information
Large letter number is Gregorian day of month. lunar month/day, sexagenary day(日辰), 24 Solor terms are also indicated. Lunar calcuation method is based on that lunar month with mid term of Feburary(雨水) is first month of a year.(雨水正月)
if there is eclipse occurance, this is indicated with 'solor/lunar eclipse' or 'Possible solor/lunar eclipse' 'Solor/lunar eclipse' mean that the eclipse is present certainly, 'Possible solor/lunar eclipse' mean that the eclipse occurance probability is more than 90%.

If you click day cell, then the detailed information for the day is displayed. (Web version do not suppport this function because the informations are displayed below month table.)

The every time information on CAL20000 is the local time of Seoul (East 135degree, GMT+9).

2011年 8月 1日
(Lunar 7月 2日 辛卯年 乙未月 戊子日)
YOUNGCHANG KOH