Armel M. Paler BSA – 3 NatSci1 ; 1:00 – 3:00 [ ]

Types of Calendar is a system that defines date, month and year. Calendars not only helps its user to identify the day but also keeps him abreast of upcoming events and appointments. Types of Calendars also helps him to efficiently manage his time.

Solar Calendar

A calendar whose dates indicate the position of Earth on its revolution around the Sun or, equivalently, the apparent position of the sun moving on the celestial sphere.

Solar Calendar is finalized on the basis of movement of Sun around the Earth. It has 365 days in a year but every fourth year is a leap year i.e. an extra day is added to the month of February.

Julian Calendar, Gregorian calendar, Bahá'í calendar, Malayalam calendar and Thai calendar are some of the examples of solar calendar.

Julian Calendar

It is introduced by Julius Caesar, was first used in 45 BC. The calendar had 365 days in a year comprising of 12 months. Every fourth year was celebrated as a leap year with a day added to February. It was the predominant calendar in the Roman world, most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and superseded by the Gregorian calendar, which was introduced in 1582. The difference in the average length of the year between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%.

The Julian calendar has a regular year of 365 days divided into 12 months, as listed in Table of months. A leap day is added to February every four years. The Julian year is, therefore, on average 365.25 days long. It was intended to approximate the tropical (solar) year. Although Greek astronomers had known, at least since Hipparchus, a century before the Julian reform, that the tropical year was a few minutes shorter than 365.25 days, the calendar did not compensate for this difference. As a result, the calendar year gained about three days every four centuries compared to observed equinox times and the seasons. This discrepancy was corrected by the Gregorian reform of 1582. The Gregorian calendar has the same months and month lengths as the Julian calendar, but, in the Gregorian calendar, years evenly divisible by 100 are not leap years, except that years evenly divisible by 400 remain leap years.

Gregorian Calendar

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Also known as Western calendar and the Christian calendar, is internationally the most widely used civil calendar. It is named after Pope Gregory XIII who had sanctioned this type of calendar on

February 24, 1582. Years in the calendar are numbered from the year Jesus Christ was born.

The calendar was a refinement in 1582 to the Julian calendar amounting to a 0.002% correction in the length of the year. The motivation for the reform was to bring the date for the celebration of Easter to the time of the year in which the First Council of Nicaea had agreed upon in 325. Because the celebration of Easter was tied to the spring equinox, the Roman Catholic Church considered this steady drift in the date of Easter undesirable. The reform was adopted initially by the Catholic countries of Europe. Protestants and Eastern Orthodox countries continued to use the traditional Julian calendar and adopted the Gregorian reform after a time, for the sake of convenience in international trade. The last European country to adopt the reform was Greece, in 1923.

The Gregorian reform contained two parts: a reform of the Julian calendar as used prior to Pope Gregory XIII's time and a reform of the lunar cycle used by the Church, with the Julian calendar, to calculate the date of Easter. The reform was a modification of a proposal made by Aloysius Lilius. His proposal included reducing the number of leap years in four centuries from 100 to 97, by making 3 out of 4 centurial years common instead of leap years. Lilius also produced an original and practical scheme for adjusting the epacts of the moon when calculating the annual date of Easter, solving a long-standing obstacle to calendar reform.

Bahai Calendar

It is used by Bahai community, has 365 days in a year and 366 days in a leap year. Interestingly, Bahai calendar has 19 months in a year and its week starts from Saturday and ends on Friday.

The Bahá'í calendar started from the original Badí‘ calendar, created by the Báb in the Kitabu'l-Asmá' and the Persian Bayán (5:3) in the 1840s. An early version of the calendar began to be implemented during his time.[5] It used a scheme of 19 months of 19 days (19x19) for 361 days, plus intercalary days to make the calendar a solar calendar. The first day of the early implementation of the calendar year was Nowruz, while the intercalary days were assigned differently than the later Bahá'í implementation. The calendar contained symbolic connections to prophecies of the Báb about the next Manifestation of God termed He whom God shall make manifest.

Armel M. Paler BSA – 3 NatSci1 ; 1:00 – 3:00 [ ]

Bahá'u'lláh, the founder of the Bahá'í Faith, who claimed to be the one prophesied by the Báb, confirmed and adopted this calendar. Around 1870, he instructed Nabíl-i-A`zam, the author of The Dawn-Breakers, to write an overview of the Badí' calendar. In the Kitáb-i-Aqdas (1873) Bahá’u'lláh made Naw-Rúz the first day of the year, and also clarified the position of the Intercalary days to immediately precede the last month.Bahá'u'lláh set Naw-Rúz to the day on which the sun passes into the constellation Aries. Bahá'ís interpret this formula as a specification of the vernal equinox, though where that should be determined was not defined.

The calendar was first implemented in the West in 1907.

Malayalam Calendars

It is used in the state of Kerala in India, has been in use from 825 AD. Onam festival, celebrating the beginning of the harvest season in mid-August, marks the beginning of the Malayalam New Year. It has 365 days in a year.

Lunar Calendar

It is based on the motion of moon. It has 12 lunation or months comprising of 29 to 30 days as against 30 to 31 days in a Solar Calendar. In some lunar calendars like Chinese calendar, a month starts on the day of the arrival of the new moon while in others, the first day of the month is determined by the day the crescent of the moon is sighted.

Islamic calendar, Hindu calendar and Chinese calendar are some of the examples of lunar calendars.

The length of each lunar cycle varies slightly from the average value. In addition, observations are subject to uncertainty and weather conditions. Thus to avoid uncertainty about the calendar, there have been attempts to create fixed arithmetical rules to determine the start of each calendar month.

The average length of the synodic month is 29.530589 days. Thus it is convenient if months are in general alternately 29 and 30 days (sometimes termed respectively hollow and full). The distribution of hollow and full months can be determined using continued fractions, and examining successive approximations for the length of the month in terms of fractions of a day. In the list below, after the number of days listed in the numerator, an integer number of months as listed in the denominator have been completed:

29 / 1 ( 1 day after about 2 months)

30 / 1 ( 1 day after about 2 months)

59 / 2 ( 1 day after about 2.6 years)

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443 / 15 ( 1 day after about 30 years)

502 / 17 ( 1 day after about 70 years)

945 / 32 ( 1 day after about 122 years; expressible exactly in binary: 11101.10001₂)

1447 / 49 ( 1 day after about 3 millennia)

25101 / 850 ( dependent on change of synodic month value)

These fractions can be used to construct a lunar calendar, or in combination with a solar calendar to produce a lunisolar calendar. A 49-month cycle was proposed as the basis of an alternative Easter computation by Isaac Newton around 1700.[3] The tabular Islamic calendar's 360-month cycle is equivalent to 24×15 months minus a correction of one day.

Islamic Calendar

It is generally used in all Muslim-dominated countries, always consists of 12 lunation or months. Mainly used for religious purposes, this calendar helps Muslims all over the world determine Islamic holy days like Id, Moharram etc.

It is used to date events in many Muslim countries (concurrently with the Gregorian calendar), and used by Muslims everywhere to determine the proper days on which to observe the annual fasting, to attend Hajj, and to celebrate other Islamic holidays and festivals.

The first year was the Islamic year beginning in AD 622 during which the emigration of Muhammad from

Mecca to Medina, known as the Hijra, occurred. Each numbered year is designated either "H" for Hijra or "AH" for the Latin anno Hegirae ("in the year of the Hijra");hence, Muslims typically call their calendar the Hijri calendar. The current Islamic year is 1436 AH. In the Gregorian calendar, 1436 AH runs from approximately 24 October 2014 (evening) to 13 October 2015 (evening).

Each month of the Islamic calendar commences on the birth of the new lunar cycle. Traditionally this is based on actual witnessing of the crescent marking the end of the previous lunar cycle and hence the previous month thereby beginning the new month. Consequently each month can have 29 or 30 days depending on the visibility of the moon, astronomical positioning of the earth and weather

Armel M. Paler BSA – 3 NatSci1 ; 1:00 – 3:00 [ ]

conditions. However, certain sects and groups, most notably Dawoodi Bohra Muslims and Shia Ismaili Muslims use a tabular Islamic calendar (see section below) in which odd months have thirty days (and also the twelfth month in a leap year) and even months have 29.

Hindu Calendar

Calendar starts on Baisakhi, which falls on April 13, marking the beginning of the harvest season. There are 12 lunar months and every month begins with the occurrence of a new moon before sunrise. There are around 29 to 30 days in a lunar month as against 30 to 31 days of Solar Calendar.

Two types of calendar are used in India – Vikrama calendar followed by people in North India and Nepal, and Shalivahana, which is followed by devotees in South India and Maharashtra. Both the calendars have 12 months and their sequence too is same. The only difference between the two calendars is that they celebrate New Year on different months.

In the Hindu calendar, the day starts with the sunrise. It is allotted five "properties" or "limbs", called aṅgas. They are:

1. the Tithi (one of 30 divisions of a synodic month) active at sunrise

2. the Vāsara (ancient nomeclature), vāra (modern nomeclature), like in ravi-vāra, somā-vāra, etc. or weekday

3. the Nakṣatra (one of 27 divisions of the celestial ecliptic) in which the moon resides at sunrise

4. the Yoga (one of 27 divisions based on the ecliptic longitude of the sun and moon) active at sunrise time

5. the Karaṇa (divisions based on tithis) active at sunrise.

Chinese Calendar

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It believed to be the oldest calendar system in the world that is still in use. Its first ruler Huang Di invented this. However, subsequent rulers made some modifications to the calendar. A regular year in the Chinese calendar has 12 lunar months and every day starts at 2300 hrs instead of midnight. The first day of every month has to be on the day of occurrence of the new moon. An extra month is added to the second or third year of the Calendar.

Many countries use two calendars – Gregorian calendar for general use and some calendars like Hebrew, Hindu, Chinese and even Islamic for religious purposes.

Several coding systems are used for some special circumstances in order to avoid ambiguity, such as continuous day or year count.

* The heavenly stems is a decimal system. The characters of the heavenly stems are: jiǎ, yǐ, bǐng, dīng, wù, jǐ, gēng, xīn, rén, guì (Chinese: 甲乙丙丁戊己庚辛壬癸).

* The earthly branches is a duodecimal system. The characters of the earthly branches are: zǐ, chǒu, yín, mǎo, chén, sì, wǔ, wèi, shēn, yǒu, xū, hài (Chinese: 子丑寅卯辰巳午未申酉戌亥). The earthly branches are used to mark the shí and climate terms usually.

* The stem-branches is a sexagesimal system. The heavenly stems and earthly branches match together and form stem-branches. The stem-branches are used to mark the continuous day and year.

In the Chinese calendar, the days begin at midnight and end at the next midnight, but people tend to regard the days as beginning at dawn.

Currently, the time in days are scaled with hour-minute-second system.

In ancient China, the time is scaled with shí-kè and gēng-diǎn system. And there are 10 gēng or 12 shí, 60 dián or 100 kè, 6000 fēn in a day. For example:

The current Chinese standard time is 20:35:49 or 1 gēng 3 diǎn(xūshí).Purge

Currently, the days are grouped into 7-day weeks and the weekdays are marked

with the ordinal number except Sunday.

In ancient China, the days are grouped into 60-day weeks with the stem-branches.