The time it takes for light from a distant galaxy to reach Earth and the distance to that galaxy are interconnected. This is due to the fact that light travels at a finite speed, which is approximately 299,792 kilometers per second (or about 186,282 miles per second) in a vacuum.
To determine the time it takes for light from a galaxy to reach Earth, we need to know the distance between the galaxy and our planet. However, galaxies in the universe are located at vast distances, often measured in millions or billions of light-years.
A light-year is the distance that light travels in one year, which is approximately 9.461 trillion kilometers (5.879 trillion miles). So, if a galaxy is, for instance, 1 million light-years away, it means that the light we observe from that galaxy today started its journey 1 million years ago.
To provide a specific example, let's consider the Andromeda Galaxy, which is the nearest spiral galaxy to our Milky Way galaxy. The Andromeda Galaxy is located at a distance of about 2.537 million light-years from Earth. This means that the light we currently observe from the Andromeda Galaxy started its journey 2.537 million years ago.
It's worth noting that due to the expansion of the universe, the distance between galaxies can change over time. So, the values mentioned here are approximate and can vary slightly depending on the specific methods used to measure them.