why there are 7 days in a week,365 days and 12 years in a year ,whats the reason behind it?

Answer 1

http://en.wikipedia.org/wiki/WeekOrigin_of_the_seven-day_week

the seven day week is a consequence of the ancient babylonian religion. it is not anything natural. some 2600 years ago, the babylonians worshiped seven "deities": sun, moon, mars, jupiter, mercury, venus, and saturn. these were the known planets at the time. the babyloians chose to divide the day into 24 equal time periods. they chose 24 because it is divisible by a lot of smaller numbers. they dedicated each hour to one deity in order of its speed across the sky. it happens that the first hour of each day is therefore dedicated to a different deity and that day was named for that deity. the first day of the week is sunday (sun day, if you wish). the second day is monday (moon day), if you know the names of the next few days in french or spanish then you will recognize that tuesday (mardi, martes) is named for mars, wednsday (jeudi, jueves) is named for jupiter, thursday (mercredi, miércoles) is named for mercury, and friday (vendredi, viernes) is named for venus. the last day of the week is saturday (saturn day).


http://en.wikipedia.org/wiki/Hellenic_calendar
http://en.wikipedia.org/wiki/Roman_calendar
http://en.wikipedia.org/wiki/Julian_calendar
http://en.wikipedia.org/wiki/Gregorian_calendar

the number of months per year is an arbitrary choice. the romans seem to have adopted the hellenic calendar, which was divided into ten months, but later added january and february to the end in about 713 BC. january became the first month in 153 BC. this calendar also sometimes had an additional intercalary month because this calendar was only 355 days long. julius caesar instated the julian calendar in 46 BC. the months quintilis and sextilis became july and august, which are named after julius and augustus caesar, and the number of days in the calendar year increased to 365 with an additional intercalary day every four years so the intercalary month was removed. the calendar we use today is the gregorian calendar, and it is a modification of the julian calendar. aloysius lilius devised it, and pope gregory the thirteenth later instated it in 1582.
the british empire, including the american colonies, adopted it in 1752 (14 september 1752 followed 2 september 1752 in the british empire).
the union of soviet socialist republics adopted it in 1918 (14 february 1918 followed 31 january 1918 in the ussr).
greece adopted it in 1923 (1 march 1923 followed 15 february 1923 in greece).

[i actually have devised a calendar that i like. there are no non-natural units. it has two independent time units: the day and the year. each unit is based on different motions of the earth so they are independent. each of these units is additionally divided into four sub-units. the year is divided into the four seasons, and the day is also divided in to four parts]

http://en.wikipedia.org/wiki/Sidereal_day
http://en.wikipedia.org/wiki/Sidereal_year
http://en.wikipedia.org/wiki/Tidal_acceleration#Historical_evidence

the number of days per year is just the number of times the earth spins each time it orbits the sun once. the spin of the earth is slowing so there are fewer days per year than there were in the past, and the number of days per year will continue to decrease in the future. the days are becoming longer so there are fewer days per year. 375 000 000 years ago, the day seems to have been about 22 hours long so the year was about 400 days long.

Answer 2

Well - the earth goes round the sun once every 365 days (but not exactly - it would be surprising if it were exact) so there is no problem about that. Both the year and day are easily observable astronomically so that has been known since ancient times, and everyone agrees about that. A month is approximately how long it takes for the moon to orbit the earth - roughly 28 days. So there are roughly 13 lunar months in a year, but again not exactly. This was regularised (by the Romans I think) to 12 months, each slightly longer than a lunar month, to fit with the year. A week of course is one phase of the moon, to the nearest day. Some civilisations still use lunar months (Chinese for example) and still use lunar months so their year slips relative to the months, until they have to slip in an extra month to bring things back into kilter. We have to do the same with leap years - adding an extra day every now and then - to keep our year in line, because the year is not an exact number of days long.

Maybe a bigger question is why there are 24 hours in a day :-)

Answer 3

the 7 day week was defined in the middle east, more than 3 thousand years ago, as a suitable work/rest cycle.
the lunar month that is about 29 days and the lunar year that is about 356 days and 12 lunar months were also defined in the middle east.
Later the solar year, which is more reasonable way of measuring years was introduced but the number of months remained the same although they now include more days, about 365 days in 12 months. by that the solar year replaced the lunar year, except among Muslims that still follow the lunar year, and by Jews, who have a lunar year with extra month every few years to follow the solar cycle

Answer 4

Well ya got me
I figured out the 7 days, the 365 days but been tryin all morning to get the 12 years in a year.

Are you going to be nice and let me know the answer ?

Answer 5

7 days is approximately one phase of the moon.
365 has only two factors, 5 and 73
364, however factors into 4,7,and 13. Curious, no?
I believe the Hebrews had a 13-month year.
The Babylonians used a number base of 60 and were the first to divide a circle into 360 degres (60*6) or 30*12
If you postulate 5 holy days then 12 months of 30 days works out very neatly, just as 13 months of 28 days and one holy day works out pretty well.

Others believe that we once had a 360 day year to begin with. and that something gradually lengthened our year to 365 days.

Answer 6

The Mayans were the ones who formed the calandar. 12 months has to do with how long it takes the earth to go around the sun. 7 days has to do with the phases. The months itself is how long it takes for the moon to go around the earth. As for 24 hours, it has to do with the earth and its axis. The Mayans were fairly close when they made the calandar, and that was made by observing the sun and moon.

Answer 7

60 seconds = 1 minute
60 minutes = 1 hour
23 hours 56 minutes & 0.9 seconds = 1day
365 1/4 days = 1year
100 years = 1 centuary

I really like your question.
And the answer is that everything depends on the rotation speed of the earth.

Answer 8

365 days is the amount of time that it takes for the earth to rotate around the sun...

Answer 9

It's calculated on cycles of the moons orbit around Earth, and the Earth's orbit around the Sun. The axis of each, in it's orbital cycle is also a factor.

Answer 10

You mean 12 months in a year. I'm not sure but it seems to work and it's fairly similar in many nations which is quite amazing.