Question for astronomy buffs.

[grumpyduck]

Like probably many of us, I often ponder weird stuff in the shower. Most of it just comes and goes, but this thought, from a few days ago, kinda stuck in there.

We are told that the vast majority of the objects we see in the sky are anywhere from a few to several million lights-years away, i.e., at different distances. So what we see up there is the light from where these objects were a long time ago. And the universe is expanding.

So, it would seem to follow that what we see up there isn't a "real" picture: it's more like a composite picture of where all these objects were (in our viewpoint) at many different times in the past. For all we know, the constellations, as we see them, may not even "exist" any more. And that supermassive black hole at the center of the Milky Way may be a lot bigger.

And that leads to the other thought: when we see a planet, we are seeing where it was when sunlight hit it, but it's not there "now," because the light from the planet takes a while to reach us.

Did all that hot water screw up my brain?

[NewHendoLib]

1. mind blowing, isn't it!

the fact that light takes time to travel makes it all fascinating - just learned that light takes about 45 min to reach us from Jupiter, varying as Jupiter's distance from us varies. So - if Jupiter blows up, we wouldn't know for 45 min - but that's based on our perspective. I guess, anyway!

[happybird]

2. Yep!

With the planets in our solar system we are seeing them as they were minutes ago since they are relatively close. When you look at the Sun, what you see was 8 minutes ago. I used to have a sky-viewing app on my old iPad that included the times for each object. It blew my mind! Learning that shut my brain down for a bit while I processed the information and eventually came to understand it. Crazy! Sadly, I can’t remember which app it was.

[yonder]

3. Not related to your astronomy question but....

...I've often wondered why "I often ponder weird stuff in the shower" too.

I seem to do my best free form, stream of consciousness thinking during those few moments and don't know why that is.

I apologize in advance for jostling your thread.

[Irish_Dem]

5. Somewhat common event.

We aren't sure why.

Shower provides relaxation/meditation/endorphin release?

[grumpyduck]

8. No worries.

You didn't jostle it.

[Irish_Dem]

4. Yes we are actually viewing the past?

[Beastly Boy]

6. Yep.

So if you see something you like on Jupiter, grab it right away: it may not be there 45 minutes ago...

That makes sense, doesn't it?

[LastDemocratInSC]

7. That weird stuff in the shower is easily removed with spray on bleach and a brush.

[tornado34jh]

9. Well, a lot of it has to do with our view of distance

Our brains have a hard time with distance. If you were to look up at the sky and see a plane moving, it appears to be moving slowly, when in fact, it is moving at several hundred miles per hour. Obviously if it were close to the ground at that speed, it would appear very fast. But when it is say 40,000 feet up, it's not moving much, and so it appears far away. Now take that and go at a much bigger scale. The stars in the constellations all appear to be the same, when in fact they are not. If we were to take a spaceship and go to each star, they would appear at different distances. In effect, we sort of see a "2D" appearance in the night sky even though it isn't.

But how bright it is doesn't necessarily tell us how far away it is. For example, Deneb, in the constellation of Cygnus, is about as bright as Saturn is at minimum apparent magnitude, but Saturn is about 1 billion miles away, while Deneb is anywhere between 1,500-3,000 light years away. But the reason it is that bright despite being that far away is because it is white supergiant. It is between 55,000 and 196,000 times as luminous as the sun. If it were say 33 light years away, it would be as bright as a quarter moon. Space is so vast, it's hard for most of us to comprehend.

[usonian]

10. Try taking a bath. Worked for Archimedes.

And maybe you will discover the grumpyduck principle!

[grumpyduck]

11. I don't think I'd want to run naked down the street

crying "I found it!"

But thanks for the thought.

[eppur_se_muova]

12. Try reading up on the topic of "light cone" (actually a 4-D hypercone)

https://en.wikipedia.org/wiki/Light_cone

Anything outside your past light cone is invisible to you. Anything outside your future light cone cannot affect you -- its worldline and yours never intersect.