Looking Out - Looking Back


As we look out into space we look back into time...

Carl Sagan  

We see nearby objects as they were recently.
More distant objects we see as they were in the past.
...and redshifted
The observable sky is a superimposed stack of "shells" going back in time
We can only see back as far as the time when the Universe stopped being a "fireball" - before that it was opaque.
...the redshift of light from that time is so great visible light has become microwaves