The 20th century astronomer and author Robert Burnham Jr. devised this ingenious way to indicate the distance of one light-year to easily express the distance scale of the universe. By introducing light year, describing the distance of stars and planets become more understandable. He relates the light-year to the Earth-sun distance as the astronomical unit (AU). Light travels at an incredible 186,000 miles (300,000 km) per second. A light-year is the distance light travels in one year wherein a light-second is the distance light travels in one second, or 7.5 times the distance around Earth’s equator. It takes less than one light year away to travel from Mars to Earth. However, the exact distance changes moment to moment since both Earth and Mars orbit the Sun.
4.2 × 10−5 light years away is Mars from earth