TABLE OF THE DIVISIONS OF TIME
| 60 | seconds (sec.) | = | 1 minute (min.) |
| 60 | minutes | = | 1 hour (hr.) |
| 24 | hours | = | 1 day (da.) |
| 7 | days | = | 1 week (wk.) |
| 30 | days | = | 1 commercial month (mo.) |
| 52 | weeks | = | 1 year (yr.) |
| 12 | months | = | 1 year |
| 360 | days | = | 1 commercial year |
| 365 | days | = | 1 common year |
| 366 | days | = | 1 leap year |
| 100 | years | = | 1 century |
| Century | Years | Months | Days | Hours | Minutes | |||||
| 1 | = | 100 | = | 1,200 | = | 36,500 | = | 876,000 | = | 52,560,000 |
Centennial years exactly divisible by 400, and other years exactly divisible by 4, are Leap Years.
Why We Have Leap Year
The average time it takes the earth to revolve once around the sun (one year) is 365 days, 5 hours, 48 minutes, 47.8 seconds, or about 3651⁄4 days.
The change in the length of the mean sidereal day, i.e., of the time of the earth’s rotation upon its axis, amounts to 0.01252 seconds in 2400 mean solar years.
Instead of reckoning this part of a day each year, it is disregarded, and an addition is made when this amounts to one day, which is very nearly every fourth year. This addition of one day is made to the month of February. Since the part of a day that is disregarded when 365 days are considered as a year, is a little less than one quarter of a day, the addition of one day every fourth year is a little too much, and, to correct this excess, addition is made to only every fourth centennial year.
STANDARD TIME
By this is meant time which differs from Greenwich mean time by whole hours.