Same for the years. If a year actually is 365.24219 days (tropical year) and we’re adding 1 day every 4 years (.25 per year) there’s a difference of 0.00781 days or ~11 minutes per year. After a few years, aren’t we actually shifting hours? Is there a mechanism to adjust it?
In: Physics
A sidereal day is 23 hours and 56 minutes. This is the time it take for the Earth to rotate 360°.
However, we don’t use sidereal days for our normal time keeping; we use solar day. A solar day is when the sun returns in the same place in the sky on the next day, which takes on average 24 hours. It takes a bit longer than a full rotation because of the Earth orbits around the sun as well. After the Earth rotates 360°, it is no longer is the same spot it its orbit. [It needs to rotate just a bit more in order to realign the sun](http://astronomy.swin.edu.au/cms/cpg15x/albums/userpics/solarday2.jpg).
So, we don’t lose those four minutes a day because don’t use sidereal days.
Leap years compensate for how long it takes to revolve around the sun. It has nothing to do with revolving on our own axis. For leap years, years divisible by 100 but not 400 are not leap years. For example, 2000 was a leap year because it is divisible by 100, and 400. 1900 was not leap year because it is not divisible by 400, neither will the year 2100 be. So, every 400 years, we skip 3 leap years.
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