To examine the way the universe behaved in the past, astronomers
look at extremely distant objects, such as supernovae in
galaxies billions of light-years away. But how does that work?
How can astronomers look out into space and see the universe
back in time? The answer lies in the speed of light. Light waves
move very fast, about 186,000 miles per second (300,000 km/s).
Light moves so fast that as you go about your daily life, it
appears to travel instantaneously from one place to another. For
example, it takes only a few billionths of a second for light to
travel across your bedroom when you turn on a lamp. In space,
however, the distances are so immense that the time that light
takes to travel is noticeable. Going the Distance The Moon is
Earth’s closest companion, at about 239,000 miles (390,000 km)
away. Light takes around 1.3 seconds to travel that distance.
The Sun is 93 million miles (150 million km) away, far enough
that the light it emits needs about 500 seconds to travel to
Earth. We call the dista