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Why is the Sky Black at Night?

12/11/2012 10:21 AM

Considering

A/the amount of light received from a light source decrease following the square of the distance. i/e a star located twice further is only seen with one fourth of the brightness of its closest equivalent.

B/the number of light sources (stars) increase following the square of the distance range you consider and star "density" is not decreasing as far as we can see in all direction.

then then sum of light coming from the stars of the whole universe should be infinite (number of sources compensing mathematicaly for the decrease of intensity) and make the nigh sky a bright continuous light source of infinite intensity, and therefor we should not exist at all to ask this question.

However WE EXIST (almost) so we have an oportunity to answer this question.

Any answer not scientificaly sound is not valid here...but the bible was already giving an answer : see genesis...first day...

I would love to have ONE correct full answer covering any subsequent (implied) question....

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#1

Re: Why is the sky black at night?

12/11/2012 10:23 AM

Because if it were any other colour, it wouldn't be "night".

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#2

Re: Why is the sky black at night?

12/11/2012 10:35 AM

An infinite number of things too dim to see is still too dim to see. Or are you too dim to see?
(don't mean to be rude, just couldn't resist the pun)
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#3

Re: Why is the sky black at night?

12/11/2012 10:35 AM

Why is the sky black at night?

So that we can grasp the otherwise incomprehensible distances involved.

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#4

Re: Why is the sky black at night?

12/11/2012 10:38 AM

"Any answer not scientificaly sound is not valid here..."

I'd say that the same should be true for questions, as well.

How about a valid question from you, one without the religious overtones?

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#5

Re: Why is the sky black at night?

12/11/2012 10:46 AM

...but the bible was written by various different men, translated by more men many years later, then adjusted to to try and make the various books agree and then re-written and translated some more.
I think the men 10,000 years ago, never mind 2,012 years ago were probably as clever as us, but in different ways with differnt skills to those we have now. They doubtless relied on the supernatural to explain things they couldn't work out for themselves.
Mind they could still make bows and arrows and boomerangs which is more then many of us can do.
Old books are not intrinsically more correct than new books.
Just 'cos it's written down, doesn't make it true.
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#6
In reply to #5

Re: Why is the sky black at night?

12/11/2012 10:49 AM

<...Just 'cos it's written down, doesn't make it true....>

It is to some CR4 posters.

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#8
In reply to #6

Re: Why is the sky black at night?

12/11/2012 11:10 AM

OK...
Lets try this then...

The Lord said, let man make up stories to explain this lot.
And they did, and the Lord saw it was good and smiled to himself knowing that despite them getting it factually incorrect it would give them something to argue about and wage war over for centuries to come.

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It's written so it's true...
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#13
In reply to #5

Re: Why is the sky black at night?

12/11/2012 11:50 AM

Well,

While mentionning the bible version (in one of it's very first chapter) I was only trying to emphasis the fact the question is real old and was a real concern. I really don't like the religious thing at all...whatever the religion...still it is sometime interesting to know something about things you don't like.

Scientificaly it is still a "simple" question I never seen a correct "full" answer...yet it doesn't mean non scientific answers are to be considered as better at any degree.

I fell I am among the lucky ones that understand just enough to KNOW some anwers will always remain out of reach... and love it!

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#7

Re: Why is the sky black at night?

12/11/2012 10:50 AM

let me ask Albert to explain that thing again to me about the gravitational fields with enough mass to bend light..........I'll get back to you on this one..........

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#9

Re: Why is the Sky Black at Night?

12/11/2012 11:14 AM

This is Olber's Paradox. The American Museum of Natural History credits the American author Edgar Allan Poe with giving the first more-or-less correct scientific answer.

http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/cs_paradox.html

From the link: "So why is the night sky dark? The first scientifically reasonable answer was given in 1848 by the American poet and writer Edgar Allan Poe! He suggested that the universe is not old enough to fill the sky with light. The universe may be infinite in size, he thought, but there hasn't been enough time since the universe began for starlight, traveling at the speed of light, to reach us from the farthest reaches of space."

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#11
In reply to #9

Re: Why is the Sky Black at Night?

12/11/2012 11:28 AM

Brilliant reply. GA.

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#14
In reply to #9

Re: Why is the Sky Black at Night?

12/11/2012 12:01 PM

You googled the OP's question,...... didn't you?

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#17
In reply to #14

Re: Why is the Sky Black at Night?

12/11/2012 1:05 PM

I'd read a book a long time ago that discussed Olber's Paradox. (I'm an amateur astronomer.) The book mentioned the Poe answer, and that struck me as something memorable. Google merely provided the convenient link for me.

By the way, there is a slight flaw in the assumption that the sky is black at night. If our eyes were capable of seeing 'light' with a color temperature of 3 degrees Kelvin we'd see the sky evenly lit in all directions by the backround radiation from the Big Bang.

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#18
In reply to #17

Re: Why is the Sky Black at Night?

12/11/2012 1:06 PM

good for you............ I thought it was interesting.

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#21
In reply to #17

Re: Why is the Sky Black at Night?

12/11/2012 2:58 PM

GA. The OP limited his question to visible light, star light in particular, but there are more flavors of photons then just what we see. Lots of X-ray and UV coming this way, too. However, I would think the sky would be "dark" in those portions of the spectrum for the same reason it is dark in the visible.

But I do have a follow-on question: The Big Bang background radiation isn't from the stars; they didn't exist until later. Is this background similar to fluorescence, either primary or secondary? (tertiary?) Or is this more like low energy density from a finite amount of energy filling a larger and larger volume?

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#22
In reply to #9

Re: Why is the Sky Black at Night?

12/11/2012 3:27 PM

GA from me too but, one flaw I see is that black holes are not accounted for.

We now know there a supermassive black holes at the center of most galaxies.

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#52
In reply to #22

Re: Why is the Sky Black at Night?

12/12/2012 1:32 PM

There's one behind my clothes dryer. It's where my socks disappear.

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#10

Re: Why is the Sky Black at Night?

12/11/2012 11:26 AM

It looks black to us because there is not enough light to stimulate the color-sensitive cones in our eyes, even though there is light in the nighttime sky, and it has color. Away from city lights or other interfering light sources, the night sky, illuminated by moonlight is blue, similar to the sunlit daytime sky.

If the Universe is full of stars, why doesn't the light from all of them add up to make the whole sky bright all the time? It turns out that if the Universe was infinitely large and infinitely old, then we would expect the night sky to be bright from the light of all those stars. Every direction you looked in space you would be looking at a star. Yet we know from experience that space is black! This paradox is known as Olbers' Paradox. It is a paradox because of the apparent contradiction between our expectation that the night sky be bright and our experience that it is black.

Many different explanations have been put forward to resolve Olbers' Paradox. The best solution at present is that the Universe is not infinitely old; it is somewhere around 15 billion years old. That means we can only see objects as far away as the distance light can travel in 15 billion years. The light from stars farther away than that has not yet had time to reach us and so can't contribute to making the sky bright.

Another reason that the sky may not be bright with the visible light of all the stars is because when a source of light is moving away from you, the wavelength of that light is made longer (which for light means more red.) This means that the light from stars that are moving away from us will become shifted towards red, and may shift so far that it is no longer visible at all. (Note: You hear the same effect when an ambulance passes you, and the pitch of the siren gets lower as the ambulance travels away from you; this effect is called the Doppler Effect).

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#12
In reply to #10

Re: Why is the Sky Black at Night?

12/11/2012 11:35 AM

Some of that explanation sounds familiar.

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#15
In reply to #12

Re: Why is the Sky Black at Night?

12/11/2012 12:07 PM

OK, I know most of the scientific explanations you can copy/paste from internet.

They all connect the "big bang / relativity" stuff...which is a very good analysis but is only pushing the question a bit further and don't give any "full" answer...

I did not expect ANY answer to be fully acceptable, just wanted to show how this very simple problem (yet more important than ANY other) is difficult to solve.

So rather than trying to ask dificult question to clever engineers who know the complicated answer, start asking yourself simple questions no genius scientist can tell honnestly he has a simple answer...

All in all this is not wasting your time !

Of course I am kidding and I love the brain training you all provide when tricking us with technicaly funny questions !

But I was born with a very devious sense of humor.

All for now

Best seasons greetings

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#16
In reply to #15

Re: Why is the Sky Black at Night?

12/11/2012 12:13 PM

tonight I'm gonna have to lay on the front lawn and stare into space and consider all the possibilities (with a couple of beers of course) see what this place does to me?

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#53
In reply to #15

Re: Why is the Sky Black at Night?

12/12/2012 1:46 PM

Some of these answers would be easier to read if you climb down off that high horse of yours first. Just sayin'.

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#19

Re: Why is the Sky Black at Night?

12/11/2012 2:20 PM

If you subscribe to the belief that there is an infinite number of stars, then you must also believe that space is infinite, and therefore some of the stars are at infinite distance. Since the intensity of light is proportional to 1/d², then the light intensity of those is 0, since 1/∞² = 0. Also, each light source doesn't have infinite energy. And third, the effect of high gravity objects, particularly black holes, on light would have to be considered. (As you can tell, I'm not an astronomist .)

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#20
In reply to #19

Re: Why is the Sky Black at Night?

12/11/2012 2:24 PM

I think you just created your own sect

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#23

Re: Why is the Sky Black at Night?

12/11/2012 7:29 PM

And once again theoretical mathematics does not support what reality shows us with the greatest of persistence.

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#40
In reply to #23

Re: Why is the Sky Black at Night?

12/12/2012 9:10 AM

...then the model on which the mathematics is based is flawed, and deserves improvement.

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#24

Re: Why is the Sky Black at Night?

12/11/2012 7:49 PM

Wouldn't it be bright if the universe was only 6000 years old?

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#25
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Re: Why is the Sky Black at Night?

12/11/2012 8:31 PM

Don't start.

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#26

Re: Why is the Sky Black at Night?

12/12/2012 12:24 AM

Have you considered, that plenty of gases and dust Absorbing exist out there?

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#27

Re: Why is the Sky Black at Night?

12/12/2012 12:26 AM

The way I see it, it seems to be necessary for the night sky to be black or very dark to set the circadian rhythm of all living things. We all have a circadian rhythm as well as does the night blooming Cyrus and other plants and animals that are nocturnal by nature. Night has a purpose as does all other things in nature. Scientists are kept busy trying to out smart mother nature, but so far they have failed. Have fun with the subject. I, personally want to see some new thought and maybe some humor. Just think about it. The night hides lovers from their parents.

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#28

Re: Why is the Sky Black at Night?

12/12/2012 1:40 AM

It's never black except to those who are blind to the frequencies present. Your eyeballs are limited to visible light, and so, you see a black sky minus the sun. Otherwise the sky is brightly lit at all times in the infra red and microwave bands, and also brightly lit by cosmic rays, mostly from Cygnus X3.

YOU see black. The sky is bright at night.

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#54
In reply to #28

Re: Why is the Sky Black at Night?

12/12/2012 1:54 PM

"YOU see black. The sky is bright at night."

I'll have what you're having lol.

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#29

Re: Why is the Sky Black at Night?

12/12/2012 1:44 AM

Hasn't the matter in the universe only extended out to 16 Billion years? So beyond that there is no luminous matter yet? So the universe may be infinite, but it hasn't yet been fully occupied by matter, no matter how sparsely spread.

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#58
In reply to #29

Re: Why is the Sky Black at Night?

12/12/2012 6:58 PM

No, actually.

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#30

Re: Why is the Sky Black at Night?

12/12/2012 1:45 AM

Because that is the way we perceive it.

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#31
In reply to #30

Re: Why is the Sky Black at Night?

12/12/2012 2:39 AM

As stated previously I don't beleive a full answer is available.

However some answers in this forum are fully stupid (sorry, don't want to be rude).

Whatever the wave-lenght if the amount of radiated energy coming to the earth (day AND NIGHT) was infinite then the temperature of the earth (and the whole universe !) would be infinite too. Period.

The GOOD partial answer is : the amount of radiated energy in the universe is limited.

The missing part of the answer is : as the production of such energy is continuous and it's "density" remain constant (or even decrease a bit) then this energy is leaking "out" OR the container is expanding.

Black holes, universe expansion or whatever concept, though explaining how the night in dark, still hang on a very simple problem : where is this universe expanding in or leaking to...if it is not in the universe itself, providing the definition of universe exclude anything to be "out"...

Again it is no magic nor religion involved : this is just our limited understanding of the reality...

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#70
In reply to #31

Re: Why is the Sky Black at Night?

12/14/2012 3:55 PM

All of this infinite schminfinite stuff is a bunch of bollocks if one takes into account all of the dust and/or dark matter which actually veils our view of everything out there, including our own atmosphere for a good chunk of the spectrum.

We cannot see a good percentage of the stars in our local group due to the veil of matter surrounding us.

Practice opening and closing the curtains or shutters in your home and see how the light diminishes.

Do you sit around and wonder why you cannot see daylight through the entrance to your house when you close the door?

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#71
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Re: Why is the Sky Black at Night?

12/14/2012 4:25 PM
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#77
In reply to #31

Re: Why is the Sky Black at Night?

12/15/2012 12:16 PM

Speaking of black holes, I have often thought that our universe is in one. When you consider that the nearest star is 4.2 light years away, the distance from the last planet in our universe is quadrillions of miles from the nearest star outside our universe. To me this is turning out to be an interesting thread.

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#33
In reply to #30

Re: Why is the Sky Black at Night?

12/12/2012 3:38 AM

Best answer yet. GA from me.
Del

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#32

Re: Why is the Sky Black at Night?

12/12/2012 2:39 AM

A couple of things. Firstly, the Universe may be infinite (or not, we don't really know), but the part we live in, that is, the visible Universe, is not infinite by any stretch. The part containing stars is probably quite a bit larger and not all of it is visible because, like Poe said, light from it all hasn't had time to reach us. Most of it will never reach us (read on). And, as USBPort mentions, if we could see at microwave wavelengths, the sky would have a dull and remarkably uniform glow. This glow didn't start out as microwaves; it is the result of shorter wavelengths from the Primordial Fireball being stretched along with the expansion of spacetime itself.

What we see at night extends (with the help of instruments and very long exposure times and gravitational lensing) out to around 13.2 - 13.4 billion light years. I saw recently a photo of what is believed to be the most distant galaxy yet observed - a small, irregular galaxy which formed a paltry 400 million years after the Big Bang.

Interestingly - and this is where a lot of the press (and not a few science texts) get it wrong - is that objects seen at the visible edge of the Universe are today much farther than the 13 or so billion light years stated. More like 45-47 billion light-years, thanks to the expansion of spacetime meanwhile.

According to calculations, the 'comoving distance' (current proper distance) to the region emitting Cosmic Microwave Background Radiation (CMBR), which represents the radius of the visible universe, is about 45.7 billion light years), whilst the present comoving distance to the theoretical edge of the observable universe is about 46.6 billion light years - about 2% larger.

The age of the Universe is about 13.75 billion years but, due to the expansion of spacetime, Humans are observing objects that were originally much closer but are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the comoving distance at the present time) than a static 13.75 billion light-years distance. The diameter of the visible universe is estimated at about 93 billion light-years, putting the edge of the observable universe at about 46-47 billion light-years away.

There is a limit to how far we will ultimately be able to see due to Hubble's Law. It says that for sufficiently distant regions of spacetime the expansion of the Universe exceeds the speed of light - not a problem where it concerns the expansion of spacetime itself - and objects embedded in those regions will never be observable because their light will never reach us: they are receding from us faster than the speed of light. This limit is estimated to be about 62 billion light years distant but, because of the recently-discovered acceleration in the expansion rate, this limit is shrinking.

That galaxy just mentioned emitted the light we see today when it was only 40 million light years distant. Its light traveled much farther because the intervening spacetime expanded considerably in the interim. Somewhat akin to running counter to the motion of an escalator.

In short, the night sky is not infinitely bright because an infinite number of light sources are not available to illuminate it - only the ones we can see.

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#34
In reply to #32

Re: Why is the Sky Black at Night?

12/12/2012 5:40 AM

This is what I called out of subject.

- if we could see at microwave wavelengths, the sky would have a dull and remarkably uniform glow - the question is not the "color" we can see but the meer fact the power we receive is limited (at any rate).

From a biological point of view, the amount of light beeing very different between day and night, we (humans) have developed eyes that can see in de "clear" part of the day. The "night" feeling is only feeling a difference between two lightening period of very different intensity. My question is only : the light power we receive from the rest of the universe is limited...why?

I understand the stuff you mention about big bang and expansion ... this is just making no sense as ultimatly it suppose a "over universe" where things can start (from nothingness and expand in a even larger nothingness). We are still missing the correct understanding of the base concept.

I could have hask the same question 600 years ago under a little different form : when you stay on a clift why can't you see the boat any more over a certain distance. The see is flat so it is no reason you can't see as far as the spyglass can...I guess if someone had an "hubble" telescope to look in at the top of the clift, at the time it would have made no difference.

The answer was unknown at the time, and it is so clear to us now...the earth is round and if you go far enough in one direction will end up at your start point...

I expect someone will take the challenge seriously one day and discover americas like Comlubus did in 1492...

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#35
In reply to #34

Re: Why is the Sky Black at Night?

12/12/2012 8:12 AM

You remind me of some other quacks we have had visit here.

You people stubbornly insist that you are the only ones who see clearly that some strange off-the-wall phenomenon can only be explained by someone such as yourself, with such superior intelligence that only you can grasp the concepts you are touting.

I, for one, am perfectly happy to wallow in my ignorance of the night sky, secure in the knowledge that people like you will traverse life with an inflated opinion of themselves.

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#39
In reply to #34

Re: Why is the Sky Black at Night?

12/12/2012 9:07 AM

<..discover americas like Comlubus did in 1492...>

Two things:

  1. It was Columbus, not Comlubus, in the historical record
  2. As humans existed in what is today called the americas before 1492, the assertion that Columbus 'discovered' it makes no sense. Such an asserion is a Europe-centred one, and is therefore invalid in a global community.
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#44
In reply to #39

Re: Why is the Sky Black at Night?

12/12/2012 11:01 AM

Cristoforo Colombo was the LAST person to discover "America."

-A-

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#45
In reply to #44

Re: Why is the Sky Black at Night?

12/12/2012 11:21 AM

Maybe, though discovery is a personal experience.

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#68
In reply to #39

Re: Why is the Sky Black at Night?

12/14/2012 2:00 PM

I am sorry I misspelled COLUMBUS. I learned it as Christophe Colomb as my mother language is not english. So let me appologize for this mistake and certainly many other.

As an European, I sometime act and feel Europe Centred. Many time I am even France centred or simply selfish

However... When this guy with a funny name reached the place he though was India he was not aware it existed before. So it was a discovery AT LEAST and IN FIRST PLACE for himself.

When you discover something it is always a RELATIVE point of view. A discovery is not a creation...it's just becoming aware of something you or your community ignored before.

I guess the "native american" welcoming Columbus were also discovering the europeans...even though they called themself a different name at this time ! They also discovered the white men colonisation practices and get very little benefit from this discovery...

I hope this was clear and nice !

Good week end to all of you !

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#49
In reply to #34

Re: Why is the Sky Black at Night?

12/12/2012 1:18 PM

"- if we could see at microwave wavelengths, the sky would have a dull and remarkably uniform glow - the question is not the "color" we can see but the meer fact the power we receive is limited (at any rate)."

I don't recall mentioning colour, but now that you bring it up, it's sort of a neon paisley chartreuse. Naturally, having access to some good acid improves the appearance considerably.

"I understand the stuff you mention about big bang and expansion ... this is just making no sense as ultimatly it suppose a "over universe" where things can start (from nothingness and expand in a even larger nothingness). We are still missing the correct understanding of the base concept."

I defer to your superiour understanding.

"- The answer was unknown at the time, and it is so clear to us now...the earth is round and if you go far enough in one direction will end up at your start point..."

It's not round, it's an oblate spheroid - a kind of lumpy, fat, bottom-heavy egg shape (see peopleofwalmart.com), and please don't tell me I'll end up at the start point as I can barely find my car keys on a Good Day.

"I expect someone will take the challenge seriously one day and discover americas like Comlubus did in 1492..."

Yes, the Americas do need periodic re-discovering as Columbus did a half-arsed job of it.

Now for those car keys...

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#60
In reply to #49

Re: Why is the Sky Black at Night?

12/13/2012 1:19 PM

It's lovely to see someone as devious as I am!

When I say color, I mean wavelenght: unlimited amount of ANY wavelenght would still be so much we would not be here to argue !

Don't take me for more clever than I am. When I say "I understand" I mean "I realize how the relativity and current understanding of astrophysics explain things" but it doen't provide the background for it. The age of universe could be infinite, billoins of years or just a few days...it still make no sense to imagine it's start from nothingness...

I never said the earth was spherical at any rate...round was the word, round enough to go around.

I am surprise to read people explaining about any obtacles (dust...). The logic is true at any point of the universe and basicaly means : all the suns of the universe produce heap of heat from the very begining of time...yet the place looks globaly dark and cold (and IS as a matter of fact!).

So is this place is badly insulated or someone left the windowopen I don't know but it looks the "universe" is not a "closed" place...

I love the saying underlying this site page today ""Anything is possible. You can be told that you have a 90-percent chance or a 50-percent chance or a 1-percent chance, but you have to believe, and you have to fight." -- Lance Armstrong, 21st century cyclist and 6 time Tour de France winner".

Yea! this guy didn't believed a single moment...except in chemistry ...

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#37
In reply to #32

Re: Why is the Sky Black at Night?

12/12/2012 9:00 AM

<...The diameter of the visible universe is estimated at about 93 billion light-years, putting the edge of the observable universe at about 46-47 billion light-years away....>

That's a terracentric assertion.

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#50
In reply to #37

Re: Why is the Sky Black at Night?

12/12/2012 1:20 PM

Nice thing about the Universe is that looks terracentric no matter where you are!

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#69
In reply to #50

Re: Why is the Sky Black at Night?

12/14/2012 3:02 PM

you mean we are not the center of the universe? Damn, I have to redo all of my equations.

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#72
In reply to #69

Re: Why is the Sky Black at Night?

12/14/2012 5:59 PM

Stand next to my ex and everything will be fine. :)

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#36

Re: Why is the Sky Black at Night?

12/12/2012 8:57 AM

The sky is not black at night, it's just darker than it is at daytime. The vacuum of space is clear, so what appears to be black is simply an area of the sky void of a light source you can see. Put together enough of those voids, and you have a sky that looks black. Go out FAR away from city lights, and you will see that there really isn't many areas of space truly void of light. They simple don't have enough light for you to normally detect while your eyes are picking up artificial light sources.

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#38

Re: Why is the Sky Black at Night?

12/12/2012 9:05 AM

Because the space between the stars is not empty.

I have tried to quickly read all of the above posts, and most of them are correct about the distance growing and the countable number of stars within an observable distance.

I only wanted to add to the above statements that, the space between the stars is full of dust and gas and what I was told when I was a kid was called, "the interstellar medium." That even at it's thinnest this medium was about 1 particle per cm3 (of atom size or smaller). And, that over astronomical distances, could appear as a pretty thick soup.

We do not have an unobstructed view of the universe. A significant portion of the light pointed at the earth, within the observable universe, never gets here.

Frankly, I am surprised that so many smarter people than me have yet to point this out. Not that, I suppose, it really matters much in a troll post like this.

I have the utmost respect for all the usual commentators, thanks for shedding light.

-A-

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#51
In reply to #38

Re: Why is the Sky Black at Night?

12/12/2012 1:22 PM

Maybe the dust or Dark Matter is red but so thin it is invisible for near stars but becomes visible as red mist due to distance and the furthest stars look red, eventually to block out light from galaxies altogether and appear as the Cosmic Background.This is an alternative explanation to the Red Shift.

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#56
In reply to #51

Re: Why is the Sky Black at Night?

12/12/2012 2:24 PM

Well actually, um. . . . no.

Nothing actually "looks" red. The Doppler effect is called a red shift because light from distant stars has interference bands with predictable spacing which are shifted to the "red end" of the spectrum by an amount proportional to the observed distance. This is the basis for the expanding universe argument. Mostly.

I hope this helps.

-A-

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#73
In reply to #38

Re: Why is the Sky Black at Night?

12/15/2012 1:14 AM

What does you avatar refers to ? 2^64 -1 ?

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#74
In reply to #73

Re: Why is the Sky Black at Night?

12/15/2012 4:07 AM

All the Mersenne Primes were taken. :)

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#75
In reply to #73

Re: Why is the Sky Black at Night?

12/15/2012 9:47 AM

The number of grains on a chessboard, in a legend.

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#79
In reply to #75

Re: Why is the Sky Black at Night?

12/16/2012 4:41 PM

Too true. Thanks Tornado.

http://cr4.globalspec.com/user/mail/message?m=15880&u=5724

-A-

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#41

Re: Why is the Sky Black at Night?

12/12/2012 9:13 AM

<...WE EXIST...>

Arrrrrrroooooooooghaah!

Undefined "we" alarm.

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#42

Re: Why is the Sky Black at Night?

12/12/2012 9:18 AM

It's not black.

It's just a whole lot darker than daylight.

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#43

Re: Why is the Sky Black at Night?

12/12/2012 10:38 AM

Let's just say that at night time, we are in the Shadow cast by the Earth.

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#46

Re: Why is the Sky Black at Night?

12/12/2012 11:34 AM

The question should be: "Why is the sky not black during the day?"

Outside the atmosphere the sun in almost white. On earth, as the gases of the atmosphere absord some of the blue wavelenght, the sun looks yellow and the atmosphere looks blue. Also, dust and water scatter light.

Francis.

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#47

Re: Why is the Sky Black at Night?

12/12/2012 12:18 PM

Humans and other species on earth evolved based on the environment we were given. This includes our eyesight.

If our eyes had instead developed so that the night sky were fully illuminated, we would find daylight to be so blinding we could not function.

Some deep sea creatures can see perfectly at depths where essentially no light is visible to our eyes. They however, are blinded by light we can see. They evolved based on their environment...like us.

So while the night sky may seem dark to you, that is an illusion based on your daytime vision.

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#48

Re: Why is the Sky Black at Night?

12/12/2012 12:54 PM

Why is the Sky Black at Night?

As others have said, it's only our perception and for someone who has spend a considerable amount of time in the peaks of the Rocky Mountains, away from the light pollution of cities, I will say the question is not valid. In these times I've found the sky is literally filled with stars.

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#55

Re: Why is the Sky Black at Night?

12/12/2012 2:09 PM

I agree with those who mentioned the expansion of the universe and also the rods and cones of the human eye. Another thing nobody mentioned is the 85% of the matter which is dark matter. It would likely be blocking part of the light from stars, as would cold matter and dust.

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#57
In reply to #55

Re: Why is the Sky Black at Night?

12/12/2012 2:45 PM

Woops, if it exists, it's only 23% and it's transparent

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#59

Re: Why is the Sky Black at Night?

12/13/2012 11:34 AM

// -- /\(⌂x→0,⌂⌂→0,⌂⌂≈⌂y) should read /\(⌂x→0,⌂y→0,⌂x≈⌂y)

's some start

well basicly i gess it's easy to show that when the nearest star is at the "light power" distance R then the night-time light on earth ... is what we have

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#61
In reply to #59

Re: Why is the Sky Black at Night?

12/13/2012 7:06 PM

dim. That too.

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#78
In reply to #61

Re: Why is the Sky Black at Night?

12/15/2012 5:02 PM

ok this is known stuff (not by me as i'm not a ?photometrist)

anyways when you mark up new theory . . .

you dont only need to write down all dim.-s

but also a map of thought pattern leading to this very assumption

it's because when you see it - it looks easy

when you have time to revisit that after 2w or 2m or 2y

you dont get the sh¡t of what you were doing or thinking

it might be even 2h or 20 seconds /!\ (if it's very novel crap )

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#62
In reply to #59

Re: Why is the Sky Black at Night?

12/13/2012 7:17 PM

You left a comma out.

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#63
In reply to #62

Re: Why is the Sky Black at Night?

12/13/2012 7:19 PM

Grammar Nazi!

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#64
In reply to #63

Re: Why is the Sky Black at Night?

12/13/2012 7:22 PM

No, just anal.

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#65
In reply to #62

Re: Why is the Sky Black at Night?

12/13/2012 8:17 PM

Don't forget the part where it says "And then a miracle occurs"

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#66
In reply to #65

Re: Why is the Sky Black at Night?

12/13/2012 8:49 PM

Hehehehehehe. I saw that 'toon. It's a good one!

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#67
In reply to #66

Re: Why is the Sky Black at Night?

12/14/2012 10:20 AM

Probably the best cartoon ever:

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#76

Re: Why is the Sky Black at Night?

12/15/2012 9:53 AM

<unsubscribe>

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#80

Re: Why is the Sky Black at Night?

12/20/2012 7:45 AM

Hello guys,in this thread any religious book answer is not consider because its totally different situation of night..i saw last year that sky is totally looking horrar and i was feared that some thing happen at this night..

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#81

Re: Why is the Sky Black at Night?

01/09/2013 4:38 AM

A universe with no center and no edge would not confine the radiations from the heat sources no matter how long they have been cooking.

The nice new telescopes can look at an absolute black. empty part of space and after a certain amount of time an image of myriad galaxies will appear like a cloud of light. even in a spectrum our eyes are not designed to see.

It is a matter of perception.

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