In this video segment adapted from Shedding Light on Science, learn how light can be used to measure distance. Meet Kim McLeod, an astronomer at Wellesley College who studies some of the most distant objects in the universe. Even though light appears to travel instantaneously at distances here on Earth, it actually has a measurable speed of about 300,000 km/s. Kim explains how the unit of distance known as a light-year is related to the speed of light, and how the finite speed of light means that the light seen now is really a snapshot of what the object looked like in the past.