A light year is defined as the distance that light travels in one Earth year. Light moves extremely fast: 300,000 km/s or 180,000 miles/second. In one second light can travel around Earth almost four times. Nothing travels faster, establishing light as the ultimate speed limit. In 31,536,000 seconds—one year—light will travel a distance of 9.46 trillion kilometers or 5.86 trillion miles, which is 240 million times around Earth. This distance equals one light year!
