How Do Astronomers Study Galaxies and Figure Out What Happened Billions of Years Ago?

By studying galactic light that originates 300 million light-years away, astronomers can look at galaxies that are 300 million years younger than the Milky Way.

The light we see today started traveling 300 million years ago, so it represents the source galaxy as it was 300 million years ago.

Galaxies at different distances portray different stages of galactic evolution.