How long does it take for light to travel in space?

If a star is 5 million light-years away, it would take 5 million years for its light to get here. That's what the word "light-year" means — the distance light can travel in one year. You'd be looking at the star as it appeared 5 million years ago.

This is true of anything, really. For instance, it takes about eight minutes for light from the Sun to reach Earth, so you're seeing the Sun as it appeared eight minutes ago. Light travels so quickly that the difference is not noticeable for distances we encounter in everyday life.

Simply put - each light year the light must travel is how far back in time we see... The star 5 million light years away - we're seeing the star *as it was* 5 million years ago.

If it exploded 2 million years ago, we'd continue to see it's light for the next 3 million years. If it were to blow up *today*, we wouldn't know of it's destruction until 5 million years from now.

Light travels through a vacuum at slightly under 300 million meters per second. A light year is conveniently defined as the distance light travels in a vacuum in one year, which allows quick conversion to travel time when the distance is given in light years and the speed as a fraction of the speed of light.

EVERYTHING we see appears as it did in the past, not the present, since it always takes some time for the light to get from the object to our eyes (and then the signal from our eyes to our brains to trigger a conscious perception). The delay is simply increased for greater distances. For instance, if you look at the Moon in the sky, it appears roughly as it was about 1.3 seconds in the past; for the Sun, about 8 minutes. A star 5 million light years away appears as it was 5 million years in the past.

Note that occasionally, gravity bends spacetime in such a way that the delay is offset slightly. For instance, some very distant objects appear in multiple places in the sky at once due to lensing effects, and often, the separate images will have a delay between them because one of the spacetime paths from that object to us is slightly longer than the other.