Leap years are not directly connected to leap seconds, but both are for the purpose of keeping the earth's rotations in line with our clocks and calendars.
Leap seconds are added to bring the earth's rotation into line with atomic time. A leap second was added at the end of June last year, when immediately before midnight dials read 11:59:60.
Atomic time is constant, but the Earth’s rotation is gradually slowing down by around two thousandths of a second per day.
Leap seconds are therefore crucial to ensuring the time we use does not drift away from time based on the Earth's spin. If left unchecked, this would eventually result in clocks showing the middle of the day occurring at night.
The extra second can sometimes cause problems for some networks which rely on exact timings. When a last leap second was added in 2012 Mozilla, Reddit, Foursquare, Yelp, LinkedIn, and StumbleUpon all reported crashes and there were problems with the Linux operating system and programmes written in Java.
Other calendars require leap years
The modern Iranian calendar is a solar calendar with eight leap days inserted into a 33-year cycle.
The Indian National Calendar and the Revised Bangla Calendar of Bangladesh arrange their leap years so that the leap day is always close to February 29 in the Gregorian calendar.
Why Add a Leap Day?
Leap days are needed to keep our calendar in alignment with the Earth's revolutions around the Sun.
It takes the Earth approximately 365.242189 days – or 365 days, 5 hours, 48 minutes, and 45 seconds – to circle once around the Sun. This called a tropical year.
Without an extra – or intercalary – day on February 29 nearly every four years, we would lose almost six hours every year. After only 100 years, our calendar would be off by approximately 24 days in relation to fixed seasonal days days like the vernal equinox or winter solstice.
telegraph.co.uk/news & timeanddate.com
Why does February have 29 days every four years?
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