“The sidereal year is the time taken for the Earth to complete one revolution of its orbit, as measured against a fixed frame ...

A sidereal year is the time it takes for the sun to return to its same position compared to the background stars, and this takes a little over 20 minutes longer than a tropical year.

That is considered to be a sidereal year and slightly longer than a calendar year. That 5 hours, 48 minutes and 56 seconds is extra time and needs to be used. Therefore, it is used on a Leap Day.

This ‘sidereal’ year is slightly longer than the calendar year, and that extra 5 hours 48 minutes and 56 seconds needs to be accounted for somehow.” according to the Smithsonian Institute.

"Some simple math will show that over four years the difference between the calendar years and the sidereal year is not exactly 24 hours," the article goes on to say. "Instead, it’s 23.262222 ...

“The sidereal year is the time taken for the Earth to complete one revolution of its orbit, as measured against a fixed frame of reference (such as the fixed stars, Latin sidera, singular sidus ...

"Some simple math will show that over four years the difference between the calendar years and the sidereal year is not exactly 24 hours," the article goes on to say. "Instead, it’s 23.262222 ...

"Some simple math will show that over four years the difference between the calendar years and the sidereal year is not exactly 24 hours," the article goes on to say. "Instead, it’s 23.262222 ...

"Some simple math will show that over four years the difference between the calendar years and the sidereal year is not exactly 24 hours," the article goes on to say. "Instead, it’s 23.262222 ...