Nothing at all. "Leap Year" is caused by the fact that the rotation of the Earth and the orbital period of the Earth cannot be synchronized; "leap year" is the way we keep them matched up. "Light...
A cosmic year is 220 million years, the time it takes for the entire Milky Way galaxy to rotate once. If by a cosmic year you mean a sidereal year, the answer is still no. A sidereal year is the time...