Measurement Of Time

1) Day
The earth takes 24 hours to complete one rotation itself
The time taken by the earth to complete one rotation around itself is called a day. This is the earth's diurnal motion.
A day is related the diurnal motion of the earth.

2) Week
The period of seven days is called a week.
A new week starts on the eight day.
A week is not related to the motions of the moon or the earth.

3) Fortnight
A month is divided into two half's.
Each of these half is called a fortnight.
For the period of 15 days, from the new moon day till full moon day, the illumination portion of the moon as seen from the earth keeps on increasing or waxing. Similarly, for the period of 15 days from full moon as seen from the earth keeps reducing or waning.
Each of these two periods of waxing and waning is called a fortnight.
A fortnight is a period of 15 days.
A fortnight is related to the motion of the moon around the earth.

4) Month
Within the perfect period from one new moon day to the next, the moon completes one revolution around the earth. This period is called a month.
A lunar month is related to the motion is related to the motion of the moon around the earth.

5) Year
The earth takes approximately 365 days to complete one revolution around the sun.
The time taken by the earth to complete one revolution around the sun is called a year
This is the earth's annual motion
A year is related to the annual motion of the earth.

6) Leap Year
The earth takes 365 days and 6 hours to complete one revolution around the sun. As a result every year there is a difference of six hours in the measurement of a year. In order to make up this difference, every fourth year has 366 days. This year is called a leap year.
In a leap year, there are 29 days instead of 28 days in the month of February in Gregorian calendar.
A year is considered to be a leap year if that number is completely divisible by four. Year 2012 is a leap year.
The leap year starts on 21st March instead of 22nd March

Mr. Liyakat Shah
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