* Scientists use the speed of light to measure cosmic distances. Light travels 186,000 miles (300,000 kilometers) in a second. A light-year is about 6 trillion miles (10 trillion kilometers). Here are some sample distances.
* Earth to moon: 1 light-second
* Earth to sun: 8 light-minutes
* Sun to Pluto: 5 light-hours
* Sun to nearest star: 4.4 light-years
* Across the Milky Way galaxy: 100,000 light-years
* Across the known universe: 30 billion light-years