Calendar

A full calendar system has a different calendar date for every day. Thus the week cycle is by itself not a full calendar system; neither is a system to name the days within a year without a system for identifying the years.
The simplest calendar system just counts time periods from a reference date. This applies for the Julian day. Virtually the only possible variation is using a different reference date, in particular one less distant in the past to make the numbers smaller. Computations in these systems are just a matter of addition and subtraction.
Other calendars have one (or multiple) larger units of time.
Calendars that contain one level of cycles:
week and weekday – this system (without year, the week number keeps on increasing) is not very common
year and ordinal date within the year, e.g. the ISO 8601 ordinal date system
Calendars with two levels of cycles:
year, month, and day – most systems, including the Gregorian calendar (and its very similar predecessor, the Julian calendar), the Islamic calendar, and the Hebrew calendar
year, week, and weekday – e.g. the ISO week date
Cycles can be synchronized with periodic phenomena:
A lunar calendar is synchronized to the motion of the Moon (lunar phases); an example is the Islamic calendar.
A solar calendar is based on perceived seasonal changes synchronized to the apparent motion of the Sun; an example is the Persian calendar.
There are some calendars that appear to be synchronized to the motion of Venus, such as some of the ancient Egyptian calendars; synchronization to Venus appears to occur primarily in civilizations near the Equator.
The week cycle is an example of one that is not synchronized to any external phenomenon (although it may have been derived from lunar phases, beginning anew every month).
Very commonly a calendar includes more than one type of cycle, or has both cyclic and acyclic elements. A lunisolar calendar is synchronized both to the motion of the moon and to the apparent motion of the sun; an example is the Hebrew calendar.
Many calendars incorporate simpler calendars as elements. For example, the rules of the Hebrew calendar depend on the seven-day week cycle (a very simple calendar), so the week is one of the cycles of the Hebrew calendar. It is also common to operate two calendars simultaneously, usually providing unrelated cycles, and the result may also be considered a more complex calendar. For example, the Gregorian calendar has no inherent dependence on the seven-day week, but in Western society the two are used together, and calendar tools indicate both the Gregorian date and the day of week.
The week cycle is shared by various calendar systems (although the significance of special days such as Friday, Saturday, and Sunday varies). Systems of leap days usually do not affect the week cycle. The week cycle was not even interrupted when 10, 11, 12, or 13 dates were skipped when the Julian calendar was replaced by the Gregorian calendar by various countries.

Calendar subdivisions
Nearly all calendar systems group consecutive days into "months" and also into "years". In a solar calendar a year approximates Earth's tropical year (that is, the time it takes for a complete cycle of seasons), traditionally used to facilitate the planning of agricultural activities. In a lunar calendar, the month approximates the cycle of the moon phase. Consecutive days may be grouped into other periods such as the week.
Because the number of days in the tropical year is not a whole number, a solar calendar must have a different number of days in different years. This may be handled, for example, by adding an extra day (29 February) in leap years. The same applies to months in a lunar calendar and also the number of months in a year in a lunisolar calendar. This is generally known as intercalation. Even if a calendar is solar, but not lunar, the year cannot be divided entirely into months that never vary in length.
Cultures may define other units of time, such as the week, for the purpose of scheduling regular activities that do not easily coincide with months or years. Many cultures use different baselines for their calendars' starting years. For example, the year in Japan is based on the reign of the current emperor: 2006 was Year 18 of the Emperor Akihito.

Arithmetic and astronomical calendars
An astronomical calendar is based on ongoing observation; examples are the religious Islamic calendar and the old religious Jewish calendar in the time of the Second Temple. Such a calendar is also referred to as an observation-based calendar. The advantage of such a calendar is that it is perfectly and perpetually accurate. The disadvantage is that working out when a particular date would occur is difficult.
An arithmetic calendar is one that is based on a strict set of rules; an example is the current Jewish calendar. Such a calendar is also referred to as a rule-based calendar. The advantage of such a calendar is the ease of calculating when a particular date occurs. The disadvantage is imperfect accuracy. Furthermore, even if the calendar is very accurate, its accuracy diminishes slowly over time, owing to changes in Earth's rotation. This limits the lifetime of an accurate arithmetic calendar to a few thousand years. After then, the rules would need to be modified from observations made since the invention of the calendar.

JANUARY
01 : New Year's Day / วันขื้นปีใหม่
Since several decades, the westerner New Year's day is also a public holiday in Thailand. But the popular New Year's day for Thai people happens in April; it is called "SONGKRAN". The reference point is Lord Buddha's birth 543 before Jesus Christ.

12 : Thai children Day / วันเด็กแห่งชาติ
During this day, feasts organized by children happen. Children are highly respected in Thailand. In a bus an adult often gives his seat to a child but not to an elderly person. This day always happens on the second saturday in January.

16 : Teachers Day / วันครู
This day is an occasion for pupils to make merit for their teachers. Teachers are highly worshipped in Thailand for their knownledge. Pupils do not dare to embarrass their teachers.

25 : Thai Army Day / วันกองทัพไทย
During this day, Thai King Rama IX visits the army and watches a military parad.

FEBRUARY
07 : Chinese New Year's Day / วันตรุษจีน
Thailand has more than 60 millions of inhabitants. Around 6 millions of them have Chinese ancestors that immigrated to Thailand last century. So Chinese New year's day is an important public holiday.

14 : Valentine's Day / วันวาเลนไทน์

21 : Makabucha day / วันมาฆาบูชา
It came from the day when 1250 disciples from the Lord Buddha gathered to listen for the Dharma speech after Buddha's enlightment.

MARCH
No public holidays during this month.

APRIL
06 : Chakri day / วันที่ระลึกมหาจักรีบรมราชวงศ์
This public holiday commemorates the Chakri dynasty. The current King is the ninth King of the Chakri dynasty. A Royal ceremony is performed by the King to pay respects to King Rama I the Great, the founder of the Chakri Dynasty.

13-14-15 : Songkran / วันสงกรานต์
The "SONGKRAN" festival happens in the hot season in half of april. This festival happens in all Buddhist "THEREVADA" countries like Thailand, Laos, Cambodia and Burma. Songkran is the ancient New Year's Day. Now the official New Year's Day happens the 1st January. But the most popular feast is still "SONGKRAN".

MAY
01 : National Labour day / วันแรงงานแห่งชาติ
The first day of May is a public holiday commemorating the workers.

05 : Coronation day / วั�B8�าขบูชา
This day is a Buddhist public holiday. This day commemorates the birth, the enlightment and the death (entry into the nirvana) of Buddha. Temples through the country are crowded with people listening to sermons about Dharma (Buddha's teaching) and in the evening there is a candlelit procession around the main building of the temple containing the Buddha statues.

JUNE
No public holidays during this month.

JULY
17 : Asalabucha day / วันอาสาฬหบูชา
This day, which is a Buddhist public holiday, happens one day just before the Buddhist Lent day. This day commemorates the first sermon of Buddha to his five first disciples. One of them asked for being a monk. So this day is sacred because it deals with Buddha, Dharma and Sangha. There are also candlelit processions.

18 : Buddhist Lent day / วันเข้าพรรษา
This day is a Buddhist public holiday. It is the beginning of the buddhist rain retreat which last three months. During this period monks are not allowed to sleep outside their temple. Thai people buy big candles and offer them to temples.

AUGUST
12 : H.M. The Queen's Birthday / วันเฉลิมพระชนมพรรษา สมเด็จพระนางเจ้าฯ พระบรมราชินีนาถ
This public holiday is the day of all the mothers of Thailand. Especially the Queen, the mother of all Thai people. On this day all the buildings of Thailand are covered up with images of H.M. The Queen.

SEPTEMBER
No public holidays during this month.

OCTOBER
14 : End of Buddhist Lent day / วันปวารณา ออกพรรษา
This day is a religious event. The three months rain retreat is over for monks. Monks are allowed to go out of temples. Robes offering ceremonies ("THOT KATHIN" - ทอblic holidays during this month.

OCTOBER
14 : End of Buddhist Lent day / วันปวารณา ออกพรรษา
This day is a religious event. The three months rain retreat is over for monks. Monks are allowed to go out of temples. Robes offering ceremonies ("THOT KATHIN" - ทอblic holidays during this month.

OCTOBER
14 : End of Buddhist Lent day / วันปวารณา ออกพรรษา
This day is a religious event. The three months rain retreat is over for monks. Monks are allowed to go out of temples. Robes offering ceremonies ("THOT KATHIN" - ทอดกฐิน) happen everywhere in Thailand. Thai people choose temples everywhere in Thailand and bring there clothes, food for the monks. "THOT KATHIN" ceremonies last one month.

15 : Robes offering ceremony start / วันออกพรรษา เริ่มกฐินกาล

23 : Rama V 's day / วันปิยมหาราช
This is a public holiday day to commemorate the Rama V or Chulalongkorn wise reign over Thailand. Thanks to him, Thailand did not become a French or English colony even if Thailand lost his leadership over Laos, Cambodia and the northern provinces of Malaysia. During his reign, Thailand became a modern country.

NOVEMBER
12 : Loi Krathong day / วันลอยกระทง
Loi Krathong is a religious event which happens every year on the full moon of the 12th lunar month (first full moon day of November). All Thai people buy or make a "KRATHONG". It is made of styrofoam surrounded by banana leaves, with flowers and a candle in the middle. Then in the evening, Thai people go to places where there is a river, a pound to launch their "KRATHONG".

DECEMBER
05 : H.M. The King Birthday / วันเฉลิมพระชนมพรรษา พระบาทสมเด็จพระเจ้าอยู่หัว
This public holiday is the day of all the fathers of Thailand. Especially the King Rama IX, the father of all Thai people. This day is the birthday of the current Thai King. All the buildings of Thailand are covered up with symbols of the monarchy and the King.

10 : Constitution Day / วันพระราชทานรัฐธรรมบูญ
Since 1932 Thailand is a democracy. Before 1932, Thailand was called Siam and was under the total rule of the King. Now Thailand is a democracy. The king has still some power, but just a moral power over Thai people, who worship him for all its kindness and goodness. Thailand is like England : a King with no real power, a government and no president. This public holiday is the day to commemorate the Thai constitution.

25 : Christmas Day / วันคริสต์มาส

31 : New Year's Eve / วันสิ้นปี
This public holiday is the last day of the year. The New Year holiday and "SONGKRAN" period have always high accident tolls. During New year holiday 2002, 501 people were killed in traffic accidents. Many were found to have been caused by reckless and drunk motorcyclists.