Converting Lunar (chantrakati) Dates To Solar (gregorian) Dates

[onethailand]

Does anyone know of a script or routine or algorithm to convert Chantrakati dates to Julian dates or vice-versa? I need to create recurring events which are based on the Thai lunar calendar - for example, Visakha Bucha, or even Loy Krathong... but these dates, when converted to Julian dates, will naturally be different each year.

Many Thai astrology sites have conversion tools on their websites - but I need the script itself...

Thanks in advance for any help.

[Maestro]

convert Chantrakati dates to Julian dates or vice-versa

I can’t help you with the program code but I wonder if you really mean the Julian calendar, which was valid until 1582, or the currently valid calendar, the Gregorian calendar.

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Maestro

[onethailand]

convert Chantrakati dates to Julian dates or vice-versa

I can’t help you with the program code but I wonder if you really mean the Julian calendar, which was valid until 1582, or the currently valid calendar, the Gregorian calendar.

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Maestro

Gregorian. Shows how tired I am - all that searching on calendars, there are more references to Julian calendars than Gregorian... thanks for catching that.

[MarkBKK]

convert Chantrakati dates to Julian dates or vice-versa

I can’t help you with the program code but I wonder if you really mean the Julian calendar, which was valid until 1582, or the currently valid calendar, the Gregorian calendar.

--

Maestro

Gregorian. Shows how tired I am - all that searching on calendars, there are more references to Julian calendars than Gregorian... thanks for catching that.

http://www.fourmilab.ch/documents/calendar/

Great invention, Google.

[Edited in: Sarcasm re. Google]

Edited March 29, 2007 by MarkBKK

[onethailand]

Thanks for that, Mark - but no Chantarakati calendar there

http://www.fourmilab.ch/documents/calendar/

Great invention, Google.

[Edited in: Sarcasm re. Google]

[Mid]

Calendar Magic

[briley]

It's not that easy to google how to work out the future date of lunar holidays.

After many years looking at this I found that 18/11/1998 9:36:00 pm was a new moon, 03/12/1998 3:58:01 pm was a full moon. You can then add or subtract the Synod, the time between one full moon and the next or almost exactly 29.53058867 days to find the next full moon.

You can now find Visakha Bucha day, or even Loy Krathong. I haven't done the former but Loy Krathong is the first full moon in November. I suspect Bucha day is an exact number of full moons later, 3 or 4?

I did it using visual basic but am reasonably certain the MS spreadsheet - whatever it is called , I don't use it, will work it out for you.

[onethailand]

Mid - Calendar Magic supports Thai Solar (Suriyakati), but unfortunately not Thai Lunar (Chantarakati). But thanks for the help!

briley - yes, I suppose you could put it that way given that there will always be at least one full moon in November I'm not sure if the leap months or leap days would have any effect on that date though... I would imagine that it is conceivable that Loy Krathong could turn out to be the second full moon in November on occasion, since in theory Loy Krathong actually falls on the full moon in the 12th month (or more accurately, the last month known as du-an sip-song) according to the Chantarakati calendar.

Makha Bucha is the full moon of Du-an Sam, Visakha Bucha is the full moon of Du-an Hok, and Asanha Bucha the full moon of Du-an Paet, with Khao Phansa (Buddhist Lent) starting the following day.

I suppose there is some other way to calculate this, provided I can figure out when leap months and leap days are added. These are the only major days which require the Chantarakati calendar, unless some of the other festivals also base their dates on the lunar calendar.

Ultimately, I'm trying to create a perpetual Thai calendar.

[MarkBKK]

Thanks for that, Mark - but no Chantarakati calendar there

http://www.fourmilab.ch/documents/calendar/

Great invention, Google.

[Edited in: Sarcasm re. Google]

Sorry -- I thought all you needed to do was convert Lunar to Gregorian and then the rest was some simple sums. No?

If you're really stuck I've got a friend in the UK who does this sort of thing all the time who would probably be happy to lend a hand ...

[New! Improved! Lack of sarcasm!]

[briley]

That is what I have, a perpetual calandar that gives me all the Thai (and incidentally Moslem) holidays. However I realized only this year I had missed out big Buddah day.

I'm not sure how the occassional 13th lunar month is coped with in Thailand but Loy Kratong is the first full moon of November, not the second (there was a second last year if I recall).

The 13th month must be accounted for and called something otherwise all the lunar holidays would slip like the moslem ones.

What happened last year? The 12th month of 2006 had it's full moon on the 2nd november and this year the full moon of the 12th month (Ye Ping) is on the 21st November that is 13 full moons apart - if that makes sense. Since Mucha Bucha is the 3rd month (is that correct?) it was 4 months after the 12th month - so in 2006 there was a 13th month.

Does any of this make sense?

My program is in Microsoft Visual Basic v 6 if you are interested in the program or the coding? If so maybe we should move to PMs?

[onethailand]

Mark -

I thought it would be something easy as well - but the problem occurs at where extra days and months are inserted... thankfully the moon doesn't change its ways...

briley -

it occurs to me that this year might be one of those with a leap month. The leap month occurs in the 8th month - mid-summer, as it were - so there is an 8th month side one, and and 8th month side two (an exact repeat of the 8th month).

Loy Krathong - or Yi Peng - is pegged to the lunar calendar and marks the beginning of the 12th month. I guess it's safe to say it will probably always occur in November since the leap month happens before it and we know the new year (Thai Lunar) will always be in December. But there is no certainty that Loy Krathong will be the first full moon in November. It would probably be safer to say that Loy Krathong would be the *last* full moon in November, though I haven't checked this.

Just out of interest - I am a BASIC coder... in fact I was going to write the Turbo BASIC book for QUE but circumstances forced me to abandon that project.

[briley]

I think I read somewhere that Ye Peng was the first full moon but as the moons are 29.53058867 days appart then it is only once in 60 years that there are two so my calandar will work for the rest of my life! Just checked, it is 2055 when I am over 100, that the full moon is on the 1st and, I supose, the 30th of November.

OK so it is the 8th month that copes with a 13 month year. Thanks

I used to use BASIC only but I do love the ease of producing pretty interfaces with lots of things on the screen that got me onto Visual Basic, despite a loathing of MS products!

[Mid]

am i right in saying that there is only a blue moon every 60 yrs ??

knew they were rare , but didn't realise how rare ...........................

[chingching]

A good explanation of "blue moons" http://en.wikipedia.org/wiki/Blue_moon

So when does a Thai month begin ? Midnight of the day in which a full moon will occur?

If the full moon say is not till 11p.m. will the month begin on the next day?

[chingching]

i wrote this full moon cycles it adds 29 days 12 hours and 44 min to the previous date. However u can see it varies from these following given dates

us navy full moon times

http://aa.usno.navy.mil/data/docs/MoonPhase.html#y2007 which is by the us navy, so i expect is accurate. But also notice the differences are not simply adding up. Sometimes is closer sometimes farther away.

[onethailand]

i wrote this full moon cycles it adds 29 days 12 hours and 44 min to the previous date. However u can see it varies from these following given dates

us navy full moon times

http://aa.usno.navy.mil/data/docs/MoonPhase.html#y2007 which is by the us navy, so i expect is accurate. But also notice the differences are not simply adding up. Sometimes is closer sometimes farther away.

There's only one instance when it "appears farther away" - and that's after February, which of course has only 28 or 29 days, so that would be correct.

It's easy enough to get the full moon times. The trick is to turn it into a Thai lunar calendar by accurately determining which years need to add leap days, and which years need to add leap months.

In addition, a full moon occurs in the middle of a Thai month - a new moon signifies the beginning of a Thai month. I goofed when I said Loy Krathong marks the "beginning" of the 12th month, as it actually marks the middle of the 12th month.

[singburisam]

onethailand, did you ever get an answer?  I am also curious.   https://en.wikipedia.org/wiki/Thai_lunar_calendar shows that the month lengths are 29-30-29-30-29-30-29(30)-30(60)-29-30-29-30 with the numbers in parentheses showing the changes at months 7 and 8 for the two different types of leap-year ... but when does month 1 start?  Or, equivalently, when is month 8 doubled?  Is the extra month simply added whenever necessary to make Loy Kratong fall in November?  I wouldn't rule that out.  ????

 

Or is the Thai month 1 always 2 months prior to the Chinese month 1?  At least Chinese New Year is fairly well defined: "Chinese New Year falls on the day of the second new Moon after the December solstice on approximately December 22. This fails whenever there’s a leap month after the 11th or 12th month. In 2033 it will fail for the first time since 1645 (the last calendar reform)."  (Just like Gregorianers had their Y2K problem, the Chinese have a Y2033 problem!)

 

(Unlike the Thai lunar calendar where the extra month, if any, is always added immediately after month 8; the Chinese extra month placement is more flexible.)

 

It seems odd that Google doesn't find any answer.  Some Google hits are completely useless; others copy word-for-word the incomplete info at Wikipedia.

 

ETA: The quote above about Chinese New Year comes from a 52-page astronomy treatise http://www.math.nus.edu.sg/aslaksen/calendar/cal.pdf  i'd wade through it except ... it never even mentions Thai calendar.

Edited November 21, 2018 by singburisam

[singburisam]

This source https://www.timeanddate.com/holidays/th/loy-krathong shows an 11-year period with Loy Krathong dates ranging from Nov. 1 to Nov. 28.  This lends support to the conjecture that the leap month is inserted precisely where necessary to keep Loy Krathong as the first Full Moon in November!

[MJKT2014]

20 hours ago, singburisam said:

onethailand, did you ever get an answer? 

Seeing as onethailands profile says last log in to TV was over 8 years ago, you will have to wait a bit.