January 3, 2006 > Ringing in 2006 - with a new calendar
Ringing in 2006 - with a new calendar
by Tina Cuccia
As we ring in the New Year and create an ambitious new list of resolutions for 2006, there's something else we all usually do at this time of year: buy a new calendar. Rather than ponder the origins of how calendars came to be, many are more concerned about the theme of their New Year. Should it be puppies or Hawaiian beaches? How about images of Tuscany, France...cats, horses or whales?
But if you're the type to wonder how this calendaring business got started and who determined days of the week - what guy said, "Today is Monday" - you'll discover that the origin of the calendar is complicated. In fact, there is not just one calendar in use today. It has to do with your point of reference and what country you are in. Calendars used on Earth are lunar, solar, lunisolar and arbitrary.
Lunar calendars are synchronized with movement of the moon (moon phases). An example of a lunar calendar is the Islamic calendar, which has no connection with the movement of the Earth around the sun. A solar calendar tracks seasonal changes synchronized to the motion of the Sun. Examples are the Christian and Persian calendars. A lunisolar calendar - Hebrew calendar - is based on motion of the moon and the sun. Its years are related to the motion of the Earth around the Sun and its months are related to the motion of the moon.
Finally, the arbitrary calendar is not synchronized to the Moon or the Sun and has no direct astronomical basis. Still it is widely used as a unit of time. An example of an arbitrary calendar is what we refer to as the "week."
In general, a calendar is a way to organize units of time. Many diverse methods throughout the world create calendars. While some follow astronomical cycles, others are based on abstract and repetitive cycles that have nothing to do with astronomical movement. For the most part, calendars are usually based on the two most important astronomical objects: the sun and the moon.
The idea of a year is based on the Earth's movement (a complete revolution) around the sun. The length of a year is 365.242190 days, but it varies. For example, in 1900, its length was 365.242196 days and in 2100 it is speculated to be 365.242184 days.
A month is based on the moon's movement around the Earth. One full moon to the next occurs in approximately 29.5305889 days, but like the year, this varies.
Why the variation in length of the year and the month? Simply put, it has to do with gravitational force from other planets and their effect on movement.
The Christian calendar is a term that refers to the calendar most commonly in use today even though it originated in pre-Christian Rome. Christian calendar years last 365 days (or 366 days in a Leap Year). The year is divided into 12 months that have no relationship to the movement of the moon. Weeks are sets of seven days. There are two versions of the Christian calendar: the Julian calendar and the Gregorian calendar.
In 45 BC, Julius Caesar introduced the Julian calendar. His calendar was in common use until the late 1500s, when countries began changing to the Gregorian calendar. Some countries, like Greece and Russia used it into the early 1900s. The Orthodox Church in Russia still uses the Julian calendar.
The Gregorian calendar, the de facto international standard, is the calendar used most everywhere in the world today for civil purposes, including China and India (along with the Indian national calendar). The Gregorian calendar, proposed by Naples physician Aloysius Lilius and adopted by Pope Gregory XIII in 1582, corrected errors in the older Julian calendar
While the Hebrew calendar is considered the official calendar of the government of Israel, the Gregorian calendar is used for day-to-day affairs. Iran and Afghanistan use the Persian calendar, and the Islamic calendar is the standard for Muslims throughout the world. In addition, the Chinese, Hebrew, Hindu and Julian calendars are still commonly used for religious as well as social reasons.
While it's estimated that about 40 calendars are used in the world today, there is a common theme among them: providing units of time to serve the needs of society. Calendars have provided a basis for planting, migration cycles, prognostication as well as religious and civil events and holidays. But in addition to serving a practical purpose, the organization of time offers a sense of control. It can be said that calendars link mankind to the cosmos.