Posted by fuller on .
what causes a day, month and a year
Reportedly, a subconcious knowledge of fractors is said to have contributed to the choice of 24 as the number of hours for the day due to the number of equal divisions that 24 can be divided up into, 2, 3, 4, 6, 8, & 12, but history has recorded some additional information that just might have influenced the choice.
Of all the units of time that we are all familiar with, seconds, minutes, hours, days, weeks, months, and years, some naturally repeating phenomena supposedly dictated the definition of three of them. Days were easily related to the spin of the earth on its axis, months to the phases of the moon, and years to the Earth's motion around the sun. The solar (or Synodic) day, 24 hours, was clearly defined as the length of time between successive meridian passages of the sun. (It takes 23hr-56min-04.09sec for the earth to rotate 360 degrees relative to the stars, the Sidereal day.) Ancient calendars were based on the Moon's motion around the Earth, which takes ~27.32 days to revolve 360º around the earth and ~29.53 days to pass from one New Moon to the next. Obviously, the year was based on the number of days it took the Earth to complete one 360 degree revolution about the sun relative to the stars.
Ancient Babylonian calendars were based on the Moon having 12 months of alternating 29 and 30 days, giving rise to a 354 day year. It soon became clear that this 354 day calendar was rapidly getting out of synch with the actual seasons and was adjusted to keep it in step with the solar year. The Gregorian version of the Julian 365 1/4 day year was ultimately adopted, with rearanged month lengths, with a leap year every four years to account for the 1/4 day. There remained a small inaccuracy in the length of the solar year, which was ultimately accounted for by the requirement that only the century years evenly divisible by 400 qualifying as a leap year. This is the reason why the years 1700, 1800, and 1900 were not leap years, and 2000 will be.
Weeks were apparantly a result of man's desire for a repetitive cycle of time longer than a day. The length of the week has been as varied as the people who used them. 10, 4, 6, and ultimately 7 days were finally accepted as the standard length of the week. The exact origin of the 7 day week is attributed to several sources. It has been said that it originated with the Babylonians some 4000 years ago. It is also said to be of Hebrew or Chaldean origin and is mentioned in the Bible. It is said to have begun with the division of the lunar month into seven-day periods for the purpose of celebrating the creation of the world in six days with the seventh day as a day of rest. The Roman week was originally an 8 day period until around 300 A.D., when the official recognition of the Christian religion mandated the celebration of the Sabbath every seventh day. The ultimate name for the days of the week came from the Roman nad Nordic name for the planets known at that time.
Not surprisingly, the division of the day into hours was also man made. In ancient times, people felt the need for a means of dividing the day into fractions of a day. There being no natural and repetitive ocurrances that alerted the human mind to any recognizable division of time, man devised a somewhat simple means to create the division, the sundial. Sundials were supposedly first used in Egypt about 3000 B.C. A stick was placed in the ground pointing northward so that the end of the shadow would mark out a semi circle which could arbitrarily be divided into equal units of time. The Sumerians alledgedly first divided their day into six watches (three day and three night) and the Babylonians divided it into 12 equal periods. It was alledgedly the Egyptians who first picked 24 as the number of hours into which the day was to be divided. They supposedly chose 24 because stargazers noticed that the night seemed to be marked off by the consecutive rising of 12 bright stars in the sky. Being obsessed with symmetry, they then divided the day into the same 12 increments to match the night. Ultimately, many other means of measuring the accepted 24 hours of the day were devised. Hourglass clocks, candle clocks, water clocks, gravity clocks, and pendulum clocks were some of the early methods of measuring out the hours of the day.
I will be learning soon
Tchrwill must have either had a lot of time on her hands or be a really fast/accurate typist.