Thinking About Astronomical Distances Makes My Head Spin

Wow, already I’m slacking with my posting. Oh well, I just need to get into the swing of things.

So anyway, lately I’ve been thinking about an interesting fact of astronomical observation: When you look out across these huge distances you are actually looking backwards in time. This is due to the fact that while light travels incredibly fast (186,000 miles per second), it is still dwarfed by the distances between objects. For instance the nearest star to us is Proxima Centauri which is located 24.94 TRILLION miles away. Even at its incredible speed it still takes light just over 4 years to get from it to us. So when we see the light from Proxima Centauri we are seeing it as it was when the light left– 4 years ago.

And this is the closest star to us. Other objects involve much greater distances. Our galaxy, the Milky Way, for instance is about 100,000 light years across. That’s equal to about 621,000,000,000,000,000 miles. If you stand at one edge of the galaxy you’re seeing the opposite edge as it was 100,000 years ago.

While thinking about this, I came across an interesting question: If the further distance you see is further back in time, you can’t see the entire galaxy from the same time perspective. While the far edge would look 100,000 years old to you, the middle would be only 50,000 years ago and around you would be the most current. As the galaxy rotates around its axis, things should look ‘smeared’ out from our perspective. So how can we get a good idea of what the galaxy looks like if we can’t see the entire thing as it is at one time?

Interestingly enough, I came across the answer to this in a sheer matter of serendipity in a video I was watching:

In short: Yes we are seeing different sections of the galaxy from different moments in time, but because the galaxy rotates so slowly in relation to the distances the effect is negligible.

So there’s my answer. Something that bugged me for a while actually and I just accidentally stumble upon the answer while cruising YouTube. Funny how things work out that way.

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