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Timeline References
Venerable Bede in the 8th century, wrote his Historia Ecclesiastica Gentis Anglorum and used 1AD date as a bearing.
Following the Bede’s lead, historians began to use 1AD as a reference point to record chronicles.
At that time, the concept of zero was not established.
The years following the presumed birth of Christ are numbered and followed by Anno Domini (AD) which means "In the Year of Our Lord". The smaller the number, the farther back in time.
The years before Christ's birth were numbered backwards (the larger the number, the farther back in time) followed by BC standing for "Before Christ".
· This timeline is recognized by international institutions such as the United Nations and the Universal Postal Union. |
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Origins of Timekeeping—Part 3 |
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Improved communication, commercialization and transportation around the world demanded that universal standards be improved. As more countries became involved in international concerns, another designation for dating epochs has emerged to accommodate the billions of people whose culture is not Christian.
In an effort to solve this problem, “Before the Common Era” (BCE) was chosen to replace BC, and “Common Era” (CE) replaces AD.
Time Zones
In the late 1800’s, with increased international travel and communications, it became necessary to create standard time zones so that everyone could agree on the time and nations could work more efficiently.
· Sir Sandford Fleming, of Scotland, emigrated to Canada in 1845. He later became a railway engineer for the Canadian Pacific Railway and realized in a huge country like Canada, provinces were not coordinated time wise. Fleming outlined a plan for worldwide standard time.
In 1884 delegates from 27 nations met in Washington, DC, for the Meridian Conference and agreed on a system which is basically the same as that now in use.
Royal Greenwich Observatory in the UK was chosen to be the keeper of standard time because the Observatory had already established a record of accurate timekeeping for astronomical purposes.
Greenwich Mean Time, (GMT) i.e. mean solar time at Greenwich, was adopted by the countries attending the Meridian Conference.
Because the Earth turns, it is daytime in part of the world when it is nighttime on the other side of the world.
Drawing a line around the middle of the Earth, equal distance between poles, results in a circle which we call the equator. The delegates at the Meridian Conference divided the 360 degrees of the circle into 24 zones, each zone having15 degrees (24 x 15 = 360).
The delegates decided to start counting from Greenwich which is 0 degrees longitude.
Noon Greenwich Mean Time is not necessarily the moment when the Sun crosses the Greenwich meridian (and reaches its highest point in the sky in Greenwich) because the Earth has an uneven speed in its elliptic orbit and its axial tilt.
The overhead sun at noon may be up to 16 minutes away from noon GMT (this discrepancy is known as the equation of time). The fictitious ‘mean’ sun is the annual average of this non-uniform motion of the true Sun, necessitating the inclusion of mean in Greenwich Mean Time.
There are 4 days per year which are precisely 24 hours long as measured by the Sun. These days occur on or about 25 December, 15 April, 14 June and 31 August. The remaining days are longer or shorter as measured from the overhead midday sun.
Atomic clocks represent a much more stable time base.
On 1 January 1972, GMT was replaced as the international time reference by Coordinated Universal Time (UTC), maintained by an ensemble of atomic clocks around the world.
Universal Time 1 (UT1) was introduced to represent "earth rotation time".
Leap seconds are added to or subtracted from UTC to keep it within 0.9 seconds of UT1.
Despite time being measured by highly accurate atomic means, the Earth time stills rules. Should earth time and atomic time get out of step, scientists adjust time by subtracting or adding "leap seconds" on the last day of June or December.
Since 1986, GMT, with slight refinements to keep it in step with atomic clocks, has been known as Coordinated Universal Time and is still the world’s time standard.
Daylight Saving Time
To conserve energy and make use of longer days in the summer, many countries adopted Daylight Saving Time during the First World War.
· Daylight Saving Time in Canada: · At 2:00 am local time on the second Sunday in March, Daylight Saving Time begins. Clocks are advanced to 3pm, with the loss of an hour. · At 2:00 am local time on the first Sunday in November Daylight Saving Time returns to Standard Time. Clocks are set back to 1am, therefore gaining an hour.
▪ Spring Forward Fall Backward
Canada uses six primary time zones: From east to west they are Newfoundland Time Zone, Atlantic Time Zone, Eastern Time Zone, Central Time Zone, Mountain Time Zone, and the Pacific Time Zone. Each zone is one hour behind the zone to the east, except Newfoundland, which is ½ hour ahead of Atlantic.
· In Canada, Daylight Saving Time falls under the jurisdiction of the provinces: o Quebec, east of 63° east longitude, does not change to daylight time and remains on Atlantic Standard Time all year round. o Most of Saskatchewan uses Central Standard Time all year round. Small pockets of Ontario and British Columbia do not use daylight time.
Much of Africa, China, Japan, the Indian subcontinent and Indonesia do not observe Daylight Saving Time.
International Date Line
The International Date Line is the imaginary line on the Earth that separates two consecutive calendar days. The planet is divided into 24 time zones and there must be a place where a day begins, thus the International Date Line was established. Traveling west across the Line, a day is lost; traveling east across the Line, a day is repeated.
The International Date Line has been recognized as a matter of convenience and has no force in international law.
· The International Date Line sits on the 180º line of longitude away from the defining meridian that goes through Greenwich and runs in the middle of the Pacific Ocean. · · The Line is not a perfectly straight line and has been moved slightly over the years to accommodate needs of various countries in the Pacific Ocean. · In the Eastern Hemisphere, left of the International Date Line, the date is always one day ahead of the date or day in the Western Hemisphere. The position given on most maps is the line drawn by the British Admiralty in 1921.
Hours, Minutes, Seconds Our word hour, and the Greek and Latin hora come from the Ancient Egyptian har or hor, meaning "the day" or "sun's path." The Egyptians worshipped the god Horus who was the god of dawn.
The Egyptians and Babylonians divided the day from sunrise to sunset into twelve parts that are called hours. They also divided the night, the time from sunset to sunrise, into twelve hours. But the day and the night are not the same length, and the length of the day and night also changes through the year. This system of measuring the time was not very accurate.
Our ancestors figured out that by dividing the whole day into 24 hours of equal length (12 hours of the day plus 12 hours of the night), the time could be measured much more accurately.
Day and night were divided into 12 parts because twelve is the number of moon cycles in a year. This became a a special number in many cultures. A look at a clock shows the versatility of twelve—clock dials are evenly divided with six hours on each of the two sides and three hours in all four quadrants. This is why twelve and its multiples of 24 and 60 were selected for various periods of time within the day
The hour is divided into 60 minutes, and each minute is divided into 60 seconds. The idea of dividing the hour and minute into 60 parts comes from the Babylonian sexagesimal system, which is based on the number 60. This system was developed about 4,000 years ago.
12 hours before noon 12 hours from midday to midnight
A clock only shows 12 hours at a time, and the hour hand must go around the clock twice to measure 24 hours, or a complete day. To tell the first 12 hours of the day (from midnight to noon) apart from the second 12 hours of the day (from noon to midnight), we use these terms:
AM: Ante meridiem, from the Latin for "before noon" PM: Post meridiem, from the Latin for "after noon"
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