How Far Back in Time Can We See Through a Telescope?
Introduction Every astronomical observation is also an observation of the past. Because light travels at a finite speed, the images we receive from celestial objects show them not as they are now, but as they were when their light began its journey toward Earth. This article explores what that means in practice — from nearby objects within our solar system to distant galaxies — and asks a simple but profound question: how far back in time can we see through a telescope? ...