Sound can only move so fast through the air sound travels at about 750 miles (1,200 kilometers) per hour. It’s a good comparison because both sound and light travel in waves, which are affected by their movement through air and space. That change in the sound of an ambulance is due to what’s called the Doppler effect. What is a redshift? It’s often compared to the high-pitched whine of an ambulance siren coming at you, which drops in pitch as the ambulance moves past you and then away from you.
Astronomers use redshifts to measure how the universe is expanding, and thus to determine the distance to our universe’s most distant (and therefore oldest) objects.
