When we use powerful telescopes to look at distant objects, such as stars, galaxies, and quasars
in space, we are actually looking back in time. We can only see an object if light from that
object reaches us. Some of the objects in space are so far away that it may take light thousands,
millions, or even billions of years to reach earth. This measure of galactic distances in the
universe is represented by a light year. So, while the word “year” is a measure of time, the term
“light year” is a measure of distance similar to feet, kilometers, and miles, only thing is that this
is a measure of very very large distances.
The Hubble Space Telescope looked at a Galaxy called GN-z11, in 2016. This galaxy is at a
distance of 13.4 billion light-years away, so actually what we see today is how it was 13.4 billion
years ago. That is only around 400 million years after the big bang. This galaxy was probably
one of the first galaxies ever formed in the universe! In the time it took light from that galaxy to
reach us, that galaxy has actually moved further to an interstellar distance of more than 30
billion light-years due to the expansion of the universe. That is a really difficult concept to
Throughout the universe, all light travels at exactly the same speed approximated to 300,000
m/s (meters / second) or about 186,000 miles/sec. In easier to understand terms, that is
around 670 million miles in one hour. We are used to thinking that light is on instantaneously.
At those speeds, one can run around the earth seven times a second. So when you see
sunlight, that ray of light left the sun eight minutes ago and you are seeing it now.