A long time ago in a galaxy far, far away….
Not just the star wars intro, but a true statement if you’re an astronomer. You see, once we start to look deep in space at the more distant objects in the universe, we are actually looking deep in time as well. It all begins with a light year.
A light year is not a measure of time, it’s a measure of distance. When you turn on the light in a dark room, the light appears to fill the room instantly. But it actually takes a small amount of time, as light has a speed limit of 300,000,000 meters/second. If the furthest corners of your room are 3 meters from the light bulb, it takes the light approximately 0.00000001 seconds, or 10 nanoseconds, for the light to fill the entire area. Light can travel so fast, that it can circle the entire Earth almost 8 times in a single second. Travelling this fast would help you get places quickly, but you would burst into flames due to air resistance, so let’s put that idea behind us.
If you imagine travelling that speed in space, where there is no air, you could cover a distance of 9.46 x 1012 Km! This is a light year, and even though it is an incredibly huge distance, the closest star to Earth (other than the Sun) is 4.2 light years away. Imagine that even with the superpower to travel this fast, circling the Earth 8 times per second, if you wanted to visit the closest star, called Proxima Centauri, you would still need four years of non-stop travel time.
Let’s think about this for a second. If I was at Proxima Centauri, and I sent a picture of myself back to Earth, it would take four years to get there. But in the time it took to get there, I would have aged 4.2 years, so by the time it reaches you on the Earth, it’s no longer a ‘current’ photo of me, is it? Its the same for the stars. When we look at Proxima Centauri in the sky, we are seeing it as it looked 4.2 years ago. Even the light from the Sun seen by Earthlings is 8 minutes old. If the Sun suddenly disappeared (it won’t), we would continue receiving sunlight for eight minutes!
But it doesn’t stop there. Our Milky Way Galaxy is 100,000 light years across and contains hundreds of Billions of stars. And other Galaxies are even further. The closest large galaxy to our own Milky Way, the Andromeda Galaxy, is 2.5 Million light years away! This means that if we take a picture of this galaxy in the sky, we are actually seeing it as it looked 2.5 Million years ago, the way it was before humans as we know them had even evolved.
So if Star Wars was real, as some religiously claim it is, and it existed a long time ago in a galaxy far, far away, we might be able to see it happening. Though we would need a pretty spectacular telescope.