＃4 The Development of Japanese Calendars Part1

　Have you ever given much thought to the calendar? When I lived in Japan, I hardly noticed it, but now that I reside in Singapore, it’s become more apparent. One particularly notable example is the New Year. The Chinese New Year is celebrated annually, roughly from late January to sometime in February. Depending on one's religion, the date of the New Year can vary. While I was aware that New Year’s Day isn’t universally on 1 January, my curiosity led me to study it further.

　Nowadays, Japan and many other countries use the Gregorian calendar (though some also maintain the traditional calendar). Despite Japan’s adoption of the global standard, many events still follow the old calendar. I find this fascinating and worth discussing, as understanding the nuances of the calendar can offer deeper insights into Japanese culture and history.

Think about the calendar

　Calendars are so commonplace today that we hardly notice their significance. But imagine a world without them. It would be challenging to manage work, schedules with family, friends, and loved ones. To know the development of the Japanese calendar, it's helpful to first understand the history and purpose of calendars in general.

There are three main types of calendars

　As you may already know, calendars can be broadly divided into lunar, lunisolar, and solar calendars. None of these is inherently superior or inferior to the others; each type has been adopted based on what best suits a region’s lifestyle, religion, and historical context. Exploring these different types of calendars is quite fascinating.

太陰暦(Taiin-Reki) Lunar calendar

　The lunar calendar is literally based on the phases of the moon, or the moon's orbital cycle. One month is defined as the period from one new moon to the next, repeated 12 times to make a year. On average, a month in this calendar has about 29.53 days, resulting in roughly 354 days in a year. Over 16-17 years, the seasons can shift significantly.

　For example, Islam uses this calendar, which is why the dates for Ramadan and the Islamic New Year change each year. Many ancient cultures and regions also relied on a lunar calendar.

　There are advantages to using a lunar calendar. One significant benefit is its relationship with the sea. The gravitational pull of the moon and the centrifugal force of the earth's rotation cause tidal changes according to the moon's phases. This means that fishermen living near the sea can determine the best times for their work just by consulting the calendar. (For more details on the relationship between the moon and the tides, feel free to look it up.)

太陽暦(Taiyou-Reki) Solar calendar

　The solar calendar is based on the Earth's orbital period around the Sun, which is approximately 365 days per year. This is divided into 12 months, averaging about 30.4 days per month. Today, we use the Gregorian calendar, which includes a leap year every four years, adding an extra day, resulting in a 366-day year. Additionally, there are no leap years three times within a 400-year period.

　Here's a bit of trivia: originally, the odd months (1, 3, 5, 7, 9, 11) had 31 days, while the even months (2, 4, 6, 8, 10, 12) had fewer days (29 or 30). Julius Caesar adopted the Egyptian solar calendar and introduced the Julian calendar. Later, the first Roman Emperor, Augustus, made further adjustments. He extended August, his birth month, to 31 days, which shifted the lengths of the subsequent months. As a result, September and November are shorter months, while October and December are longer months.

　I hold great respect for the ancient Egyptians. Their development of the solar calendar, which is still in use today, showcases the height of their civilisation.

　There are advantages to this system as well. It is closely linked to the seasons, allowing the year to be calculated with near accuracy, ensuring the seasons occur at the same time each year. This makes it a very useful calendar for agriculture and other industries that need to track the seasons reliably.

太陰太陽暦(Taiintaiyou-Reki) Lunisolar calendar

　I believe this calendar represents the collective wisdom of people throughout history. It combines the principles of both lunar and solar calendars with the power of mathematics and astronomy. Since both lunar and solar calendars were crucial to people of the time, they successfully merged the best aspects of each. It should never be dismissed, even if it has its flaws.

　Efforts were made to align the month with the lunar cycle and the year with the solar cycle. The result was the introduction of leap months, creating a 13-month year, requiring seven leap months over a 19-year period. This system was used for a long time, especially in China, Southeast Asia, and Japan. It was also adopted in Babylonia and ancient Greece.

　In other words, understanding the Japanese calendar and culture begins with knowing the lunisolar calendar.The power of the calendar in history.

The Power of the Calendar in History

　Calendars are indispensable, and everyone relies on them. However, ordinary people cannot create them. This gives calendars a certain power. In other words, the ability to publish a calendar became a symbol of authority. This phenomenon can be observed worldwide in History.

　In China, from the time of the Han dynasty BCE, each change of dynasty was marked by a review and correction of the calendar, which was then distributed to the people and vassal states. This demonstrated the new dynasty’s capability to manage time and signalled the beginning of a new era. People could easily understand from the calendar that "the king has changed."

　In China, the calendar was revised over 40 times throughout its more than 2000-year history. It’s a form of political manoeuvring, but I believe that learning and development progress in this way.

　Of course, similar phenomena occurred in Europe and elsewhere. The most famous example is the Gregorian calendar, which is still in use today. In 1582, Pope Gregory XIII reformed the Julian calendar, which had been in use for many years. The specifics of the reform are not detailed here, but it was also strongly politically motivated.

　At the time, the Reformation was in full swing, and Protestantism was emerging. The Catholic Pope created and distributed a new calendar to assert Catholic power and influence. Acceptance of the calendar became a clear indicator of allegiance, with Protestant states such as England and Germany resisting its adoption.

　There was also a calendar revision during the French Revolution of 1789, which is quite fascinating! Considering that the calendar was changed even amidst the abolition of the monarchy and a fundamental transformation of the country, it underscores the calendar's role as a symbol of power. This illustrates just how influential the calendar was.

　In this French Revolutionary calendar, a day was divided into 10 hours, each hour into 100 minutes, and each minute into 100 seconds. Such a drastic change is quite remarkable, isn't it?

　Although there have been many different circumstances, the calendar we use today has evolved through numerous revisions and examinations throughout history. We can only be grateful for the wisdom of our ancestors.

What Was the Japanese Calendar Like?

　The history of the Japanese calendar is quite unique. Unlike other countries, Japan historically did not experience significant external pressures from foreign nations or major social upheavals such as the fall of dynasties so often. This may explain why the calendar remained unchanged for a long time. Although China and the Korean Peninsula are neighbouring regions, they were not as close as the Strait of Dover between England and France. As an island nation surrounded by the rough Sea of Japan, it was challenging for foreign enemies to reach Japan.

　However, as expected, errors can accumulate if an old calendar is used for too long. Japan experienced the Warring States period, and when peace was restored afterwards, the need and momentum for calendar revision increased. This occurred during the Edo period (1603-1868). Later, during the Meiji period, Japan faced substantial external pressure and began to modernise, prompting another round of calendar reform.

　In my next article, I will discuss the development of the Japanese calendar in more detail.

Summary

　I hope you have become a little more interested in calendars. Calendars are the product of advanced mathematics and astronomy. When you consider the people who created them without the aid of computers, don't you think they were accomplishing tremendous feats? It's also humbling to realise that the stars, moon, and sun can be seen from anywhere in the world, reminding us that despite our different races and ways of thinking, we have all been on the same path throughout history.

　Now, let's explore how the calendar was thought about, used, and changed by people in Japan.

Thank you for reading!