how far a light year
by John Carl Villanueva on September 10, 2009. 1 light year is the distance light can travel in vacuum in one yearâs time. This distance is equivalent to roughly 9,461,000,000,000 km or 5,878,000,000,000 miles. This is such a large distance. For comparison, consider the circumference of the Earth when measured at the equator: 40,075 km. This visible-light image shows the galaxy dubbed UGC 3789, which is 160 million light-years from Earth.