Why is the Sky Black at Night?

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

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)
Del

Why is the sky black at night?

So that we can grasp the otherwise incomprehensible distances involved.

...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.
Del

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

It is to some CR4 posters.

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!

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..........

Brilliant reply. GA.

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

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

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?

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.

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

Some of that explanation sounds familiar.

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

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?

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

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 .)

I think you just created your own sect

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

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

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

Don't start.

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

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.

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.

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

I'll have what you're having lol.

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.

No, actually.

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...

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?

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.

Best answer yet. GA from me.
Del

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...

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.

<..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.

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

-A-

Maybe, though discovery is a personal experience.

"- 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...

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 ...

<...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.

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

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

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.

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.

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-

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

All the Mersenne Primes were taken. :)

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

Too true. Thanks Tornado.

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

-A-

<...WE EXIST...>

Arrrrrrroooooooooghaah!

Undefined "we" alarm.

It's not black.

It's just a whole lot darker than daylight.

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

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.

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.

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.

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.

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

// -- /\(⌂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

dim. That too.

You left a comma out.

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

Probably the best cartoon ever:

<unsubscribe>

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..

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.