Who Invented The Calendar ?
The Calendar is a system
for arranging the year into
days, weeks and months.
Historians donot know who or when mankind invented the first calendar, probably early man when he first carved a notch into a stick
or a bone which marked the passing of each full moon.
Notched bones used to record moon phases have been found in Africa and Europe dating back to about 20,500 BC.
What is the Origin or Etymology
of the word Calendar
Kalendae or calends
was the first day of each month
in the ancient Roman calendar
Middle English and Anglo-French calender .
Medieval Latin kalendarium,
from the Latin word for accounting books.
The Gregorian & Julian Calendar
The Gregorian is the Calendar in use today
The civil day in ancient cultures was made up of "Watches". The length of the
watch varied with the season, and were called seasonal or temporal hours.
They were related to the length of the Suns time above the horizon.
This method was known as far back as 1800 BC and was used until the end of the
13th century AD in Europe. At that time it became inconvenient to use because
of the invention of the mechanical clock. The seasonal method was uneven and
the mechanical clock had an even 12 hours for day and 12 hours for night.
The 12 comes from Babylonian
2 x 12 = 24 (5 x 12 = 60).
They did this rather
than using the base 10. This is known as the Sumerian Sexagesimal System. based on the number 60.
And it has carried to this day.
We use 60 SECONDS in a MINUTE
60 minutes in an HOUR.
The civil day now begins at midnight local time. However the Julian day still starts at noon.
From the 2nd century AD until 1925 astronomers counted days from noon to noon. Primitive tribes used dawn to dawn for a day. The Babylonians, Jews and Greeks counted a day from dawn to sunset and sunset to dawn.
The Hindus and Egyptians day began at dawn. The Romans and Teutons began their day at midnight.
Today the system used for the calendar is the MEAN SOLAR DAY.
Mean Solar Day is the average of a solar day because the length of the day varies slightly during
the year as the Earth rotates around the Sun. The orbit of the Earth makes the Sun appear to move eastward each day relative to the Stars.
The Solar Day is about 4 minutes longer than the Sidereal Day.
A Mean Solar day is
24 hours 3 minutes 56.55 seconds
of mean sidereal time.
A Sidereal Day is
23 hours 56 minutes 4.1 seconds
of mean solar time.
For more information
How We Keep Time
Our clock and calendar measure the movement of the Sun, the Moon and the Stars as seen from Earth. That's how mankind keeps time and how we became timekeepers.
A day comes from the rotation of the earth on its axis, which takes about 24 hours, and the time of day comes from the Sun appearing to travel across the sky at about 15 degrees every hour.
The cycles of the Moon's phases is used to measure a Month. The moon takes 29.5 days to return to the same point in the sky, as referenced to the Sun, this is called a synodic month. There are about 7 lunar phases as observed from the Earth.
One year is the time taken for Earth to complete one orbit around the Sun relative to the stars, and is called a sidereal year. However, we measure a year to be the period between two successive spring equinoxes known as the Vernal Equinox and is on or about March 21, and this period is called a tropical year. The tropical year is about 20 minutes shorter than the sidereal year.
How fast is the Earth spinning?
about 1040 miles/hr - 1670 km/hr - 0.5 km/sec
How fast is the Earth revolving around the Sun?
about 18.5 miles/sec - 30 km/sec
How fast is the Earth,
along with the Solar System
moving around the Milky Way Galaxy?
about 155 miles/sec - 250 km/sec
How fast is our Milky Way Galaxy moving through space?
about 185 miles/sec - 300 km/sec
Take the 2007 calendar and add the number of days
of each of the 12 months
and it will equal 365 days for the year.
The 2007 calendar begins
on a Monday and ends on a Monday
which comes to 52 weeks and one day. .
7x52 = 264 + 1 = 265 days in a year.
When there is a leap year it is 52 weeks
and 2 days (366 days in the year)
A Mean Solar day is:
24 hours 3 minutes 56.55 seconds
A tropical year is:
365 days 5 hours 48 minutes 46.3 seconds
This can vary whenever there is a leap second.
Civil time is occasionally adjusted by one second increments to ensure that the difference between a uniform time scale defined by atomic clocks does not differ from the Earth's rotational time by more than 0.9 seconds. Coordinated Universal Time (UTC), an atomic time, is the basis for civil time.
See regulation ISO-8601,
Comments & Awards
For the History of the Calendar
Dionysius Exiguus die-uh-nish-e-us _ egg-zig-u-us
History of The Zero
History of Time-Keeping
History of BC-AD and Y2K
History of the Western Calendar
Days, Weeks, Months, Year origin
Gregorian, Julian and Roman Calendars