Article I, Section 8, of the Constitution, which enumerates the powers of Congress and provides Congress with the authority to make all laws necessary and proper to carry them out; also referred to as the elastic clause.
There is an exact numerical answer to this question. By definition, 1 light year is exactly 9,460,730,472,580,800 meters. By definition, 1 mile is exactly 1,609.344 meters. So, 1 light year is exactly 5,878,625,373,183 and 849/1397 miles, by definition.
A light year is how far light can travel in a year. Light travels at 186,000 miles per second, the speed limit for the universe. So in a year a ray of light covers about 6 trillion miles. Think about it this way - in one second light can travel round earth 7 times! Imagine how far it gets in a year.