# How far can one look into space while relying on light in the visual spectrum?

Put the other way around. From how far does visible light reach the Earth to be observable by a telescope that operates in this spectrum?

Gas clouds for instance absorb light. A star behind such a cloud would be not observable, because its visible light does not reach us.

• ...for example, UV light at 100 nm emitted by a $z=7$ very far star (more likely, a galaxy!), reaches us as visible red light at $\lambda=(7+1)\times 100$ nm $= 800$ nm. So, what was UV becomes visible and what was visible becomes infrared and hence there isn't a consistent loss of luminosity in the visible spectrum within small red shift of $z<10$. – AstoundingJB Sep 12 '13 at 20:03