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Measurement of Time - At a Glance - 1
Introduction
One of the problems encountered by the mass media when transmitting around the world events of universal interest - such as football games - is that it is not the same time in every country. When people in one part of the world are getting up people in another part are going to bed. This is because the world is divided into Time Zones.
What is Time
Scientists believe that the Universe is made up of three dimensions, length, mass and time. Each dimension can be measured. Time is measured in:
- years which are counted consecutivelydays,
- weeks and months by calendarshours,
- minutes and seconds by clocks and
- time zones by lines of longitude.
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Write a few sentences to explain what the disadvantages are of depending on sundials for the correct time, especially in Britain.
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Years
Over 4000 years ago stone circles were used to position the Sun and the Moon.Stonehenge in England was built by Stone Age people in around 2,700 BC. Originally it consisted of 30 upright stones their tops linked by lintels to make a continuous circle.
An artists impression of how Stonehenge may have looked when it was first built
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Task 2
Make a list of all the reasons why it is so important to know in advance what the date will be.
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Its use remains a mystery but the stones
were set to act as some kind of observatory to measure time through the movement of the Earth, Moon and Stars. The layout of the huge circle of stones marked the midsummer sunrise and midwinter moon rise.
Over 2,700 years later - Stonehenge as it looks today-
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Task 3
Make a classroom collection of examples of the calendars used by different races and religions. Perhaps the children who brought the calendars could explain to their classmates how they differ.
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 About 3500 years ago the Babylonians who lived in the Middle East began to measure time more accurately using sundials. They divided what we now call a year into 360 days. Each month was 30 days long making 12 months in a year.
The time by this sundial is 3 o'clock
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Task 4
Select a series of dates which may be meaningful.
Work out how many years between events.
For example:
The end of the Second World War and your birth date.
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To improve the accuracy of the length of the year the Egyptians added five extra days to the Babylonian year. Each year they used these five extra days to celebrate the flooding of the Nile.
These Ancient (Lunar) years were based on the phase of the moon each night. The first night a new moon rose over the horizon was counted as the first day of the next month.
The Julian Calendar invented by Roman scientists
In 47BC Romans scientists changed the year again. They based their (Solar) year on the way the Earth revolves around the Sun.
They called it the Julian calendar after Julius Caesar. They thought that some months should be lengthened to make the total of 365 days in the year.
They abandoned the Egyptian method of just adding five extra days to the end of the year.
The names of the months we use today are based on Roman names.
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The Solar year meant that, for the first time, a calendar could be calculated in advance for any year. However, the calculations proved to be not quite right and so in 1582 a modified calendar, adding leap years, was introduced by advisors to Pope Gregory XIII. The Gregorian calendar is used in Britain and many other countries today.
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Many countries of the world, including Europe, use the Christian calendar. This means that years are counted from the birth of Jesus Christ.
BC - means Before Christ
Years which passed before the birth of Christ are followed by BC. For example 50 BC means fifty years before Christ was born.
AD - Anno Domini
Years which have passed since the birth of Christ are sometimes followed by the letters AD which is Latin for Anno Domini, meaning the Year of our Lord. For example 50 AD means 50 years after the birth of Christ.
Dates without letters infer AD.
To find out how many years there are between BC and AD dates the two numbers must be added together. For example between 50 BC and 50 AD there are 100 years.
Sometimes dates are written with a 'c' (circa) in front of the number, for example c 1234. This means roughly about that time but not exactly that year.
Other countries and religions use different calendars. For example the Jewish calendar, The Chinese calendar, and the Muslim calendar.
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