This seven minute Hubblecast video helps explain how Hubble “looks back in time” to see the Universe as it was billions of years ago.
Hubblecast 68: The Hubble time machine
For episode 68 of the Hubblecast, Hubble transforms into more than just a telescope — it becomes a time machine! How can Hubble “look back in time” to see the Universe as it was billions of years ago? Dr. J explores the vast scale of our Universe, explaining how Hubble can be used to grasp cosmic distances, view very distant galaxies, and even explore our own past.
Source: Hubble Space Telescope