Many types of calendars.

Many cultures were developed in different parts of the world and a separate calendar was created and maintained by each culture to count time. Though a few of these calendars are now outdated, many of them are still being used for religious festivals.

Solar, Lunar and Lunisolar are 3 main types of calendars. The Maya calendar, Egyptian calendar etc are examples of solar calendars, while the Islamic calendar is a purely lunar calendar. Lunisolar calendars have lunar months and years, but the period is adjusted to average solar year by taking an extra lunar month after certain years.

A brief summary of these calendars is given below to get idea of changes in these calendars.

The Jewish calendar (Lunisolar) 3761 BC

This calendar is based on lunar changes. It has 12 or 13 months in a year. An additional 13th month is added 7 times in a period of 19 years. This calendar is still used for religious purposes.

The Chinese calendar (Lunisolar) 2637 BC

This calendar was based on lunar changes. It was having 12 or 13 months in a year with the first 6 months of 29 days and the remaining 6 months of 30 days each. An additional month was added every 2 or 3 years. New Years day according to this calendar is regularly celebrated in China.

Maya calendar (Solar) 2000 BC

This calendar was first solar calendar. It had 18 divisions of a year, each of 20 days and remaining 5 days were counted as bad days at the end of year. This was the first known solar calendar having 365 days in a year.

Egyptian calendar (Solar) 1321 BC

Though this calendar was based on lunar changes, it was changed to solar type to have 12 months each of 30 days.The remaining 5 days were celebrated as festival days at the end of year. King Tolemi 3 had suggested adding a day to festival days every 4th year to make calendar more accurate, but this suggestion was not accepted.

Babylon calendar (Solar) 1200 BC

This calendar was initially based on lunar changes, later this calendar was changed to solar type to have 12 months each of 30 days and an additional month of 30 days every 6th year. A week of 7 days, a day of 24 hours, an hour of 60 minutes, and a minute of 60 seconds have came from this calendar.

Roman calendar (Solar) 753 BC

This calendar initially had only 10 months and the remaining 61 days of winter season were not counted. It was modified by Numa Pompilius to have 12 months and 355 days in a year. Decimvir modified this calendar many times but still the Roman calendar was inaccurate until Julius Caesar changed it completely.

Greek calendar (Lunisolar) 433 BC

This calendar was based on lunar phases until Meton shown relation between solar years and lunar years in 433 B.C. He suggested adding 7 lunar months in a cycle of 19 years. Thus it was changed to lunisolar calendar, and was used before Julian calendar.

Julian calendar (Solar) 45 DC

Julius Caesar while in Alexander city of Egypt was very much impressed by the Egyptian calendar and the suggestion of Tolemi 3 to add an extra festival day to every 4th year, When he returned to Rome city he made many changes to the Roman calendar. 5 days were added to different months and a leap day to every 4th year. Being very simple to use and more accurate it was accepted and popular.

Hindu calendar (Lunisolar) 79 AD

This calendar is based on lunar phases with an additional month in every 3rd year to adjust with solar year. We have to subtract days or months to correct discrepancies in long period. Most of the Hindu festivals are celebrated according to this calendar.

Islamic calendar (Lunar) 79 AD

This is pure lunar calendar as it is never adjusted with solar year. It has 12 lunar months having either 30 or 29 days in a month with 11 leap days in every 30
years. Leap days are distributed in the period to have a leap day every 2nd or 3rd
year. Due to this, Muslim festivals migrate through all seasons in 33 years periods.

Gregorian calendar (Solar) 1582 AD

Pope Gregory 13 advised a new rule i.e. no century year will be a leap year unless it is divisible by 400). ThIs modified Julian calendar was called the Gregorian calendar. We have discussed this calendar in detail in later topic.

Persian calendar (Solar)

This calendar was designed by Omar Khayyam in the 12th century. It had 365 days in a year and 8 leap years in every 33 years. Accuracy of this calendar is better than the Gregorian calendar.

Proposed calendars 

After last papal bull many calendar reforms were But having some disadvantages they were not accepted. In these calendars extra calendar days were added to weekdays.

Romme calendar (Proposed) (Solar)

This calendar also called as French republican calendar had 12 months and 36 weeks, each month having 30 days and each week (called decades) having 10 days making total of 360 days in a year. The remaining 5 days were added as 31 to 35 dates to last month as an extra calendar days. In leap year 6 days were taken as extra days.

Comte calendar (Proposed) (Solar)

This calendar had 13 months and 52 weeks each month has 28 days a week has 7 days. Here a month can be accurately divided in 4 weeks. An extra day is added to 13th month as 29th day every year and leap day is counted independently.

World calendar (proposed) (Solar)

This calendar was proposed by Achelis. This calendar had 12 months with 4 fixed quarters. First month of each quarter having 31 days while other months having 30 days, Extra days were added as `leap day as 31st day of June and ‘world day’ as 31st day of December. This calendar had an advantage to use it repeatedly.

Months and days in different calendars

The idea of 7 days week with names for days was first used by Babylon culture in their calendar about 700 BC. This idea of week and days was picked up by Jewish peoples. Roman calendar got this idea from Jewish calendar. In 321 A.D. King Constantine implemented week and days successfully.

Most of calendars were based on lunar changes in their initial period before they realised that cycle of nature is associated with sun. Few calendars stopped using lunar cycles and accepted solar based calendars. e.g.

1. Babylon calendar which had 12 months of 30 days and an extra month of 30 days after 6 years to adjust remaining 5 days.
2. Egyptian calendar which had 12 months of 30 days and 5 remaining days were celebrated as festival days.

Other calendars started adding extra lunar months to specific years to adjust with solar calendar. E.g. Jewish calendar, Greek calendar etc.

As a lunar cycle was named as a month, the month became 30 days approximately. When solar calendars were started they also had months of approximately 30 days. Old Roman calendar was neither lunar nor solar initially. This calendar also had 30 or 31 days in a month.

Thus an average no of days in a month came to be 30. Probably due to the lunar cycIe.

The Roman calendar was started in 753 B.C., when it had only 10 months each of either 30 or 31 days. It was 61 day short as compared to solar year, 10 months were named as Aprils. Martius, Mayes, Junius. Quintilis, Sextilis, September etc.

In 715 B.C Numa Pompilius added 2 months i.e. January of 29 days as 12th month and February of 28 days as the 11th month. He also changed no of days of last 6 months from 30 to 29.

Thus, the total of all months became 355. For remaining days he suggested to add an extra month.

Decimvir –  a body of ten persons changed sequence of months to make January the 11th month and February the 12th month. They also started adding an extra month to even years.

Meanwhile Julius Caesar was impressed by an Egyptian calendar and suggestion of Tolemi 3. He changed the numnber of days in the months to make total of 365 days in a year with an extra day as leap day in the month of February. In the Julian calendar odd months had 31 days and even months had 30 days except February having 29 days in common years.

After Julius, Quintilis month was renamed as Julius (July). Sextilis month was also renamed as Augustus as King Augustus (octavious) had managed to clear mistakes in counting leap days. An extra day was added to Sextilis from February month to make Sextilis of 31 days and February of 28 days in common years. A day from September was given to October and a day from November to December.

Thus it is very clear that the number of days in a month depends on division of 365
days to no of months and there is no other reason for specific no of days in a month.


In the Roman Empire, the old Roman calendar was being used since 753 BC when foundation of Rome city was done by King Romles. This calendar had gone many modifications by following rulers of Roman Empire. Julius Caesar had modified this calendar so that to have 12 months and 365 days in a year. With a simple rule to predict leap year. According to the rule, every 4th year was a leap year, This calendar became popular and was being used in Europe even after many countries had accepted Gregorian calendar.

Mean solar year. i.e. the time required for earth to rotate around sun is 365.2422 days. While a Julian year is of 365.25 days. Thus every year difference of 0.0078 days was getting accumulated to create 12 days difference in 16th century. To correct this error in 1582 Pope Gregory 13 advised to add a new rule to the Julian calendar. The rule was ‘no century year will be a leap year, unless it is divisible by 400’. After Gregory this modified Julian calendar was named as the Gregorian calendar.

As Gregorian calendar has minimum error of 26 seconds per year as compared to mean solar year, it was accepted all over the world and still we are using it. Gregorian calendar as we know very well has 12 months in a year i.e, January to December and 7 days in a week ie. Monday to Sunday. Months of this calendar cannot be divided to an equal parts or number of weeks. In spite of worldwide acceptance of Gregorian caleudar other calendars like Hindu calendar, Islamic calendar etc, is still used for religious purposes.

Names of months in Gregorian calendar

Gregorian calendar is a roman calendar having 12 months, out of which 5 months are named from Roman gods. January from Janus the god of gates, March from Mars the god of wars, April from Aphrodite i.e. Venus the god of beauty, May from Mayaa the daughter of Atlas, and June from Juno the wife of Jupiter.

February is named from word `Februar’ Remaining months are named from number of months in roman language. Quintilis – five, Sextilis – six, September – seven, October – eight, November – nine, while December – ten. Quintilis and Sextilis were renamed as Julius and Augustus respectively.

Advantages of Gregorian calendar

Religious information of other calendars and other events can be printed along with the dates of Gregorian calendar so that both Gregorian calendar and religious calendars are used simultaneously,

Advertises can be done every year as Gregorian calendar is printed every year. Useful articles can be given yearly on back pages.

Disadvantages of Gregorian calendar 

  1. The Gregorian needs to be printed yearly leading to a big economical loss worldwide.
  2. Days and dates of a month never correlate with months either in the same or other year.
  3. Month cannot be divided in accurate no of divisions or weeks, due to
    which we cannot easily sum up weekly data to form monthly data.

Nation wide acceptance of Gregorian calendar

Though Gregorian calendar is popular all over the world today, it was not accepted by all countries at the same time. People were not ready to accept change being done in Julian calendar.

In India this calendar is used regularly but still it is not accepted. But, officially India has accepted the new solar calendar which was suggested by Dr. Meghnad Saha. This calendar had 12 months out of which last 6 months were having 30 days. 2nd to 6th months were having 31 days and the first month having either 30/31 days depending upon leap day.

Many of the Asian countries and Islamic countries have not yet accepted Gregorian calendar though they are using it regularly

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