Time Zone Conversion

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Measurements of Time

Time is one of the few fundamental qualities that are in existence today. It cannot be defined or clarified using other qualities; time is simply defined through measurement. Although we do not always have records of how time was kept, throughout history we can find evidence that civilizations were trying to measure time. Time has been divided into different lengths, from seconds, minutes and hours during the day, to weeks, months, seasons and years, but ultimately the day and the year have been the two natural cycles which we have continually based time around.

The initial measurements of time
Very little is known about how time was measured in prehistoric ages but there is evidence that people were trying to measure it. For example, Stonehenge was built over 4000 years ago and it now appears as though its alignment traced seasonal or celestial events.

Days were initially divided simply into daylight hours and the night rather than any smaller subdivisions, and it was the calendar which was the first measurement of time to come into existence. In the Tigris-Euphrates Valley, which is today in modern Iraq, the Sumerians devised a calendar around 5000 years ago. This was divided into 30 months, each day was divided into 12 and each of these 12 was divided into 30 parts. Initially this year was 360 days long but they later added 5 days on so that it accorded with the solar year more accurately.

The earliest Egyptian recorded calendar was based on lunar cycles. However, this civilisation later realised that the "Dog Star" in Canis Major (what we today refer to as Sirius) rose next to the sun exactly every 364 days. Thus they devised a 364-day calendar according to this knowledge. This appears to have come into existence around 3100 BCE so the two methods were actually developing simultaneously.

Around 1000 years after they devised their calendar into 30 parts, in 2000 BCE, the Sumerian civilization furthered their system of dividing the year into a method which our current system is based upon even today. This was the Sumerian Sexagesimal system, which was based around the numbers 60 and 12. There were 60 seconds in a minute, 60 minutes in an hour and, roughly (60x60), 360 days in a year, plus a few more added on. There were also 12 hours in every day and night, and 12 months to the year. So from such an early period there existed measurements of time which would maintain timekeeping for us until the present day. They were aware that the year was 365 days long with an extra 6 hours but this was ignored, so after centuries this calendar fell out of sync with the seasons.

Records from around 5000 to 6000 years ago show that the civilizations in North Africa and the Middle East had also started to supplement their calendars with clocks to record time during the days. The Sumerians had already started to segment their days, and next to do so were the Egyptians.

They built four sided monuments so that shadows would fall throughout the day, producing a kind of sundial so that the day could be partitioned into morning and afternoon. Later, other markers were added to subdivide the day even further. Around 1500 BCE, this method had progressed to a point that the sundial was elaborate enough to be able to divide the day into 10 parts, plus 2 parts of "twilight hours" in the morning and evening. When Rome dominated the world, a substantial effort was made to produce an accurate calendar. The Sumerian Sexagesimal system was accepted as accurate, but the Romans believed that even numbers were unlucky. As a result, months were divided into either 29 or 31 days, with the exception of February (which had 28 days). This only added up to 355 days, so an additional month was added every second year. However, this soon made the calendar so far off that when Julius Caesar came into power he reformed the system, making the months 30 and 31 days long. Furthermore, to take care of the 6 hours, every fourth year was made 366 days long. This calendar was known as the Julian Calendar and has been used as the basis for our calendars today.

Measuring Time
As time is a fundamental quality, it has been measured in different ways by various societies. As previously mentioned, the Sumerians introduced the idea of 60 seconds to an minute, 60 minutes to an hour, and 24 hours to a day, but the Egyptians also experimented with other methods. These included tools to measure the astronomical variations such as the merkhet. It was used to mark time throughout the night by determining with other stars crossed the meridian.

A further example was the Egyptian development of the water clock around 1500 BCE, one of the earliest time keeping devices which did not depend on celestial activities. It was used to determine what the time was at night, although it may have been used in daylight hours also. Such was the popularity of this method that it is still used in areas of 21st century North Africa.

Mechanical clocks began to be used as a measuring device of time in about the 14th century. Initially these clocks were difficult to regulate due to the heavy amount of driving force which they needed to keep time. However, the heavy driving weights were later replaced and over time clocks have developed into the accurate time keeping machines which they are today.
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