- Light travels at a finite speed (300,000 kilometers every second, 1 light-year per year).
- The light we see now left the object some time in the past.
We see distant objects as they appeared some time ago.
- The more distant the object the more ancient the light.
- Distant objects provide an opportunity to observe the Universe
as it was in the distant past.
- Owing to the inverse square law, which makes more distant
object appear fainter, it is challenging to observe the most distant
objects in the universe.
- Sensitive telescope like the Hubble Space Telescope
and the Keck Telescopes provide the light gathering capability to
see the most distant objects in the universe, and thus probe
the state of the universe very early in its history.
- You can look out farther and farther to a time when
the Universe was opaque owing the the high density of ionized gas.
- This time was only 300,000 years after the universe began.
- Observations of radio light originating from this time has enabled scientists to
derive the age and bulk contents of the universe to surprising precision.