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Update : April 25, 2020

### Leap year

• A year is a “Leap Year” if
(a) it is a non-century year and is divisible by 4 (for non century years)
(b) it is a century year and is divisible by 400 (for century years)
• Add a day to February for the leap year.
• Rationale :
The earth takes 365.2422 days to orbit the sun. So, the solar year should be 365.2422 days.
We take a civil year to be 365 days.
The difference adds up to .9688 days in four years.
This led to the first part of the Leap Year calculation.

For four centuries (400 years), the Leap Year formula over-corrects by about 3 days,
This lead to the second part of the Leap Year calculation.
• Why do we add a day to February?
According to a story, February used to have 30 days.
One day was taken off and given to July to honor Julius Caesar with a 31-day month.
Another day was taken off and given to August to honor Augustus Caesar with a 31-day month.
So, it is given back a day in a Leap Year.

### Leap month

• A common solar year contains 365 days.
• A common lunar year contains 355 days.
• The difference is 10 days.
• The difference becomes 30 days (or so) after three years.
• To keep the two calendars in sync, the lunar calendars introduce a 13th month.
Burmese/Myanmar calendar calls that month “Second Waso”.
• There is another correction for some Burmese / Myanmar years requiring “Wah Gyee Htutt”.

### Leap second

• Scientists later proposed the use of Atomic Clock.
• A second or two is added to synchronize the atomic clock with the earth’s [slowing] revolution.
• The correction can affect some hardware and software that use 60 seconds for a minute.

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