Why is the sky dark at night?

Cecil's Columns/Staff Reports
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Why is the sky dark at night?

Cecil missed the big reason why the sky is dark at night: The redshift. First, the farthest stars we can see are 13 billion light years away which is about the same time the Universe formed (not 10 billion). But, beyond that is the boom from the big bang. That in itself should illuminate the sky.

However, the farther away we look, the faster stars appear to be moving away from us. The faster stars head away from Earth, the redder their light becomes. That light quickly enters the infrared spectrum, and is invisible to the human eye. This is why radio telescopes (which pick up light that has redshifted into the radio frequency) are used in astronomy, and when Hubble took pictures of those vast distant star fields, the pictures were taken with an infrared camera.

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First of all, the furthest objects we can see are actually more like 40 billion light years away. Yes, we can see them, even though this is more than the age of the Universe: They were closer when they emitted that light.

Second, cosmological redshift isn’t actually the same thing as Doppler redshift: It’s a consequence of the expansion of the Universe directly, not of relative motion.

Third, while it’s true that distant stars are redshifted, that’s not the primary reason why the sky is dark. Even if we could see every star in the observable Universe at its un-shifted spectrum, the sky would still be dark. Cecil had it right: It’s dark because the Universe isn’t old enough yet.

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Of course, Chronos has it right, but seeing the Hubble Ultra Deep-Field images, obtained la decade+ after Cecil’s writing of article, make a person ponder it even more, LOL. There’s a LOT more stars/galaxies waaaaay out there we didn’t see or even imagine (for the most of us anyways) until said images were obtained.

I still take a look at those images now and then and just sit and try to really comprehend the hugeness/numerousness of everything around us. Too big to really ‘feel’ the bigness overall to me. Amazing. Can’t wait for the Webb telescope to launch/go operational in 2018/2019-ish (fingers crossed!).

We’ve come a long ways atronomically-speaking since that article :slight_smile:

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Blasphemers! It is dark at night because Apophis has eaten the Morning Boat and Ra is sailing the Evening Boat through the Underworld! Jackals will devour your entrails for this!

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Styx and stones, dude.

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Cecil is correct, as far as there’s not enough stars to fill the sky. But he leaves unanswered why the sky between the stars is dark: because our eyes are insensitive to its color.

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Well, this the universe has aged since he wrote the original article after all…

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Do we have any idea how old the universe would have to be for the night sky to not be dark? I assume it’s probably far enough in the future that the Earth won’t even be around anymore, but for the sake of the question, let’s pretend Earth will last just long enough.

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[QUOTE=The Perfect Master]
The oldest stars are about 10 billion years old, meaning that the greatest distance starlight can have traveled is 10 billion light-years. So the only stars we could possibly see are those within a 10 billion light-year radius of us
[/QUOTE]

I’m nt seeing how both these statements can be true?

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OK, analogy: Recently my mom went on a trip to Antarctica, which, while not the most distant spot on Earth, is realistically pretty close to it. The first leg of her trip was getting to the Cleveland airport. Suppose that, at the airport, she saw a neat postcard, and mailed it to me. I get it a couple of days later, by which point she’s at the Ross ice shelf. I now have a postcard from someone who’s clear on the other side of the planet, but the postcard only traveled a few miles.

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It’s more accurate to say that there are different ways of measuring distances on that sort of length scale. Relativity makes it sort of hard to define distance in a way that is very intuitive or matches what we consider to be distance on a more local scale. Most astronomers won’t even give a distance for very distant galaxies, they’ll just report the redshift.

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There’s a Cleveland joke there, but there always is.

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“Olbers’s Paradox”? Good grief. Another one of Cecil Adams’s mistake’s.

As I have pointed out many times, you don’t need expansion, age of the Universe or any such thing.

Simple thermodynamics. The reason the far off sky isn’t white hot is because the nearby sky isn’t. Our chunk of space isn’t blazing hot (ignoring that pesky star and it’s friends nearby as a statistical aberration), so what we see locally is pretty much what we see at a distance. We get the same energy as we send out. Not all that much on a grand scale. The local energy available in a good size piece of the Universe is remarkably sparse.

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It’s worth mentioning that a Universe that has a finite age does not automatically suggest that the observable Universe is of finite size. The classic example of such a model is the Milne model, which can be seen as the limiting case of FLRW cosmology. This is because the existence of a finite-sized observable Universe in an otherwise infinite Universe depends on whether there is a beginning in conformal time rather than whether there is a beginning in cosmological time. That said imposing certain realistic restrictions ensures the observable Universe is of finite size.

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I’m afraid your argument is not very convincing as the idea behind Olbers’ paradox is that the flux in and out of a chunk of space being finite is incompatible with the assumptions made, whereas the observed flux is finite.

Simply stating the flux is observed to be finite does not resolve the paradox, the resolution is that the assumptions made in setting up the paradox are incorrect.

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In fact light that we see now was emitted by objects that were no more than 5 billion light years away from us when the light was emitted (assuming the concordance model).

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It’s definitely true that great care should be taken when discussing distances, though the standard concept of distance in cosmology isn’t too counter intuitive and if you like ‘converges’ with the local concept of distance on a smaller scale.

Reporting of galaxies’ redshifts has more to do with that is what is actually being measured and that converting redshift to distance depends on the model being used.

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Unknown to education and science are the true workings of fire, water, air, light, magnetism, sound, sight, cold, hot, electricity, earthquakes, tides – and I could go on and on. I ask you, without knowing the truth of such things, how in bloody hell can one determine the simple working of our universe?!Like every cell, molecule, quark, planet, moon or star incorporates a black hole at its nucleus. Instigated reactions to a black hole produce its atomic reactions.

INSTIGATED REACTION is the black hole’s intake or its nutritional feeding of Bruce’s Stuph (particles).

Like all cells etc, our Sun spews its info cells or atomic energy. This energy atomically interacts creating heat, creating light with most of what it encounters, the smallness of Bruce’s Stuph (dark matter, energy) being one exception.

From this encounter or collision, created light feeds on the Aura or Info Cells (Bruce’s Stuph) of what it has come in contact with. Using this continuous magnetic energy connection, info cells of Earth are affectively transported to the sun to be used as nutrition or fuel of its black hole. This of course means we’re no longer #1 on the food chain!

Our sun is a cold, cold activated black hole. It appears to us as being hot and bright but it is not. What we observe as a fiery object is in fact collision or reaction between the force emitting from this black hole and the accumulation of packed STUPH – the sun’s digestive system if you like.

When you stand back from a fire you no longer feel its heat. The sun being no exception; we do not receive heat and light from the sun’s outer fire!

If we could see into the center of the Earth it would appear to us as being hollow (black hole). It’s the same for all cells of matter.

The Earth’s digestive system is that of the sun’s, the difference being size, speed and quantity. To explain these statements multiply the heat and light of just one meteor (shooting star).

Go out on a dark, starry night; every star that you can see is producing food (dark matter) that feeds our Earth’s black hole! The energy created from this food is like any other cell and spews from its poles. Our Earth’s atmosphere, including everything out from its black hole, has and is being created from this energy! A black God if you like!
Think HOT as being nuclear particles orbiting in chaotic orbit directions and Cold being chaotic nuclear particles orbiting harmonically in same orbit directions. (cause a reaction) blow on your hand.

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Pure anti-knowledge.

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I assume that this Forum will be reaching young people in pursuit of an education.

The education taught is what will be needed to advance or secure a comfortable financial future.

This thread is not to disrupt your education but is meant to prod an educated person into the capability of changing things of our world for the better. I believe that by knowing the truth of what is taught through Education and Science will allow this.

PS - Student Loans sending people into years of debt is a bummer. With education selling the wrong bill of goods you might just try and get your money back!