What is Time? The Calendar

What is Time? Time and The Calendar

In the time of dreams, two brothers, the Bagadjimbiri, come out of the earth as dingoes. They turn into two giants in human form and grow so tall that their heads touch the sky. Nothing exists before this: no trees, no animals, no people. The brothers come out of the earth just before the dawn of the first day. A few moments later they hear the call of a little bird, the duru, which always sings at the break of day, so they know it must be dawn. They see plants and animals and give them names. Once named, they come to life.

This Dreamtime creation myth from the Karadjeri Aboriginals of Australia is retold, orally, always in the same form, with the storyteller connecting to and being part of this beginning of time, at once inside the past and a part of the present. The Karadjeri believe that at the point of creation a fundamental rhythm is established, the call of the little bird at daybreak, so that a definition of time is imposed on human­kind by the natural order of things.

Origins of the Modern Calendar

The history of humankind’s measurements of days, months and years is the history of civilisation and, the conflict between sacred and secular political forces. It has propelled us through a history of ideas and understanding to a point at the start of the third millennium where we can measure the beginnings of the universe itself, rather than just rely on articles of faith, myth or simple conjecture.

Earth at the centre of the universe...

Our view of our place in the universe has moved on from the geocentric perspective of our forbears.

The Ancient World, with its immense reserves of knowledge stretching from the ancient Chinese to the Greeks, Babylonians and Vedic Indians, struggled to explain the rhythm of the year using mathematical and astronomical observations that were, by the end of the first millennium, the envy of an embarrassed Europe cloaked in the Dark Ages. The balance of knowledge then shifted, with ideas and learning flooding through Europe, resulting in the powerful cultural synthesis of the Renaissance and ultimately causing the separation of sacred and secular authority over the instruments of time. This is significant because religion and what has been termed organised superstition had played the primary role in controlling the lives and minds of humankind for as long as the skies and the stars have been relied on for succour and inspiration.

Definitions of the Astronomical Year

There are many different types of year, and the differences fuel the twists and turns in the story of time and the calendar.

The length of the year depends on where you measure it from. Our perceptions of time have changed and developed as science and technology have improved the accuracy of its measurement over the past 4000 years.

Lunar Year

This is the most easily observable type of year and it formed the basis of many cultures’ early government of time. As each month starts at the new moon and lasts for 29.5306 days this was generally translated into alternating months of 29 days (hollow months) and 30 days (full months). This gives a year of 354 days: too short by 0.3672 of a day of the true lunar year, so in order to redress the balance, a leap day every third year had to be inserted. (The addition of days or other units, like seconds, to balance the calendar, is known as an intercalation.) To make this calculation more accurate, a further leap day would have to be added every 10 years.

Over time, lunar years become out of sync with the seasons which are determined by the solar calendar. Several cultures, including the ancient Chinese and Greeks, used a combination of lunar and solar years by adding leap months and combining the seasonal cycles with the moon’s phases (the time from one new moon to the next), creating in one common solution a 19-year solar cycle which coincided with 235 lunar months.

Solar Year

There are a number of recognised forms of the solar year, all necessary because of the slightly elliptical rotation of the earth around the sun:

  • The tropical year – marks the year of the sun’s passage between two vernal (spring) equinoxes. The seasons are fixed and the length of the year is 365.242199 days. Generally speaking tropical year is used when the solar year is discussed.
  • The sidereal year – marks the passage of the sun relative to a fixed star. The length of the year is 365.256366 days.
  • The anomalistic year – marks the passage of the sun at the point of the perihelion, when the earth is nearest to the sun. The length of the year is 365.259636 days.
Perihelion explanation. What is Time? These fantastic Worlds

The Perihelion for 2000 CE

The next post looks at the use of different calendars.

Some other posts of interest.