pariah

maybe a dumb question

sight _is_ instantaneous right? i mean, we can see distant stars, billions of miles away. but if one of those stars went out, it would take light speed for us to see it dissapear, or explode or what not.

what we see is from objects absorbing different frequencies and the other colors coming back right? if u shine purple on red it will look blue. so if an object far away (lets say the sun), suddenly dissapeared (mmk for our example, goes nova), after the sun goes supernova it will be 8 minutes until we actually SEE it go supernova. right???

so why is it that we can see stars? b/c they are _always_ broadcasting at as? but as the earth rotates we lose sight of some and gain site of others...so quickly??

i fucking suck

Arken

I'm not quite sure what your question is. We see everything almost instantly from the moment that the light from whatever object we're looking at hits our retinas. There is obviously an infinitessimally short delay between that time and the time the information reaches the brain, but it's so short that it's unnoticable.

The reason we can see stars is because they are constantly emitting light. We can't see them in the daytime because of a combination of simply the sun being bright and that brightness then being reflected in the atmosphere making it even brighter.

pariah

if something happens farther away, does it take longer for us to see it?

we observe two events, A and B

event A happens 8 billion miles away at 12:00.

event B happens 64 billion miles away at 12:00.

which do we see first?

Friar Bellows

Yes, they're continually "broadcasting", emitting electromagnetic radiation. Of course they only emit such radiation for a finite amount of time. If the Sun went supernova (won't happen as far as our theories are concerned) it would take roughly 500 seconds before we knew anything about it.

Depends what clock the 12:00 refers to. If it's your own private clock, then the events obviously happen at the same time. If it's a kind of standard cosmic clock (say, calibrated to the cosmic background radiation) then you'll see event A first.

Arken

A much more interesting question to me is why we can only see so few stars when there are countless billions that we should be able to see. The most common answer I've heard is interstellar dust obscures them. Considering that our galaxy alone contains several hundred billion stars and we can only see a couple of thousand from earth, the amount of interstellar dust must be truly staggering.

Quantum Ninja

The intensity of the light decreases the farther away you are from the source. So the light coming from the stars that are really really really far away would be too dim for our eyes to detect.

Imagine two identical stars; both uniformly release the same amount of light energy per unit of time. Star A is 10 light years from us. Star B is 1,000 light years from us.

Intensity (power/sq. area) is indirectly proportional to the square of the distance from the source.

Star A will look 10,000 times brighter than Star B (10E-2 / 10^-6 = 10E4).

This is why the sun looks so bright. There are stars that release much more light energy than the sun, but they are so far away that the relative intensity is miniscule.

If you've ever looked at the Andromeda galaxy with your naked eye, you should know what I mean. It looks like a little blotch of fuzz that's just barely noticeable. That's millions and millions of suns all emitting light, and it's difficult to spot. And Andromeda is our closest neighboring galaxy. Most others are way too faint to be detected by your naked eye.

Rhaedas

Several possibilities...one, dust reducing the light. Add a few particles of dust for many millions of light years, and that's a lot of stuff for the light to shine through.

Also, tied in with the dust issue, is that there are many more stars than the human eye can see. Just look at some of the Hubble Deep Space pictures, and you'll see a part of the sky that's full of galaxies, yet looks black to the eye.

pariah

aaaaahah!!! i was right (sort of...)! wierd...i thought for sure i was wrong.

so what is the "speed of sight"? light i suppose, since that is what allows us to see objects.

Arken

As I said, slightly less than light really simply because you have to factor in the time it takes for the light that hits the retina to register in the brain but that difference is infinitessimally small.

Interesting about the intensity thing, Quantum Ninja, but we still are not seeing anywhere near the number of stars we should be seeing within our own galaxy and, as I said, I have heard it explained as the obscurity of cosmic dust.

Gawdawful

What about Dark Matter?

Dark matters are dark matters. Enlighten this dim bulb, please. {Refering to myself of course.--Ed.}


Warren in Oklahoma