Comments on: Why is the sky dark at night? http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html Brain candy for Happy Mutants Wed, 22 May 2013 00:19:00 +0000 hourly 1 http://wordpress.org/?v=3.4.1 By: SamSam http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1551990 SamSam Tue, 09 Oct 2012 11:42:00 +0000 http://boingboing.net/?p=185596#comment-1551990 They don't. It's not suggesting that the telescopes can see light that hasn't reached us yet. They're saying the oposite -- that the light that <i>has</i> reached us from the edge of the universe has been travelling a really long time -- 13 billion years -- and is light from when the universe was young. They don’t. It’s not suggesting that the telescopes can see light that hasn’t reached us yet. They’re saying the oposite — that the light that has reached us from the edge of the universe has been travelling a really long time — 13 billion years — and is light from when the universe was young.

]]> By: Jesse http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1551200 Jesse Mon, 08 Oct 2012 15:04:00 +0000 http://boingboing.net/?p=185596#comment-1551200 Distant galaxies *are* moving away from us. Redshift is a measure of recessional velocity. You don't get to pick and choose which kinds of motion are "real" and which aren't. If I run away from you really fast and shine a light in your direction, you can measure the redshift of the light and be confident that I am moving away from you. It's the same with distant galaxies - sure, the cause of the motion is cosmological in nature, but motion is motion. Those suckers are receding from us. I'm assuming what you're getting at is that the motion of distant galaxies is due to the expansion of the universe, not dynamics. That the galaxies are not being repulsed by some force, but are being carried along by space itself. Distant galaxies *are* moving away from us. Redshift is a measure of recessional velocity. You don’t get to pick and choose which kinds of motion are “real” and which aren’t. If I run away from you really fast and shine a light in your direction, you can measure the redshift of the light and be confident that I am moving away from you. It’s the same with distant galaxies – sure, the cause of the motion is cosmological in nature, but motion is motion. Those suckers are receding from us.
I’m assuming what you’re getting at is that the motion of distant galaxies is due to the expansion of the universe, not dynamics. That the galaxies are not being repulsed by some force, but are being carried along by space itself.

]]> By: Guest http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1551071 Guest Mon, 08 Oct 2012 08:10:00 +0000 http://boingboing.net/?p=185596#comment-1551071 "So, you want to know about quantum entanglement? Just read The Book!" - "I couldn't find anything about quarks in there, the first chapters are all about who begat whom..." “So, you want to know about quantum entanglement? Just read The Book!” – “I couldn’t find anything about quarks in there, the first chapters are all about who begat whom…”

]]> By: joe blough http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550824 joe blough Sun, 07 Oct 2012 22:03:00 +0000 http://boingboing.net/?p=185596#comment-1550824 well, the series *is* called "minute physics" so i guess the fast talking kind of comes with the territory. well, the series *is* called “minute physics” so i guess the fast talking kind of comes with the territory.

]]> By: Tom Giebel http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550790 Tom Giebel Sun, 07 Oct 2012 20:12:00 +0000 http://boingboing.net/?p=185596#comment-1550790 I thought it was odd that they would put together a video like this without referring to it as Olbers' Paradox. I thought it was odd that they would put together a video like this without referring to it as Olbers’ Paradox.

]]> By: Jizzle Jammer http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550783 Jizzle Jammer Sun, 07 Oct 2012 19:53:00 +0000 http://boingboing.net/?p=185596#comment-1550783 THE wiki THE wiki

]]> By: desiredusername http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550764 desiredusername Sun, 07 Oct 2012 18:30:00 +0000 http://boingboing.net/?p=185596#comment-1550764 I think that refuting that common sense explanation was the main point of the video.  brhat-sama tatha samnam. gayatri chandasam aham. masanam marga-sirso ham. rtunam kusumakarah. I think that refuting that common sense explanation was the main point of the video. 

brhat-sama tatha samnam. gayatri chandasam aham. masanam marga-sirso ham. rtunam kusumakarah.

]]> By: Jasonbe http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550620 Jasonbe Sat, 06 Oct 2012 23:25:00 +0000 http://boingboing.net/?p=185596#comment-1550620 Why is the sky dark at night?   Because we're in our own shadow. :] (why it's colder, too) Om buhr buvhatsva. Tat savitur vareniam. Bargo devasya demahi.  Diyo yoha ha pracho bayat! Why is the sky dark at night?  

Because we’re in our own shadow. :]

(why it’s colder, too)

Om buhr buvhatsva. Tat savitur vareniam. Bargo devasya demahi.  Diyo yoha ha pracho bayat!

]]> By: joe blough http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550613 joe blough Sat, 06 Oct 2012 23:02:00 +0000 http://boingboing.net/?p=185596#comment-1550613  that's been covered too. eventually all the interstellar dust would be excited by the infinite amount of light and start to glow as well. dust can't explain the darkness of the night sky.  that’s been covered too. eventually all the interstellar dust would be excited by the infinite amount of light and start to glow as well. dust can’t explain the darkness of the night sky.

]]> By: Robo-Design http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550550 Robo-Design Sat, 06 Oct 2012 19:26:00 +0000 http://boingboing.net/?p=185596#comment-1550550 doesn't it have something to do with the fact that the star is a finite size and its light radiates?, so the farther the object is from the star the less light rays would hit it. doesn’t it have something to do with the fact that the star is a finite size and its light radiates?, so the farther the object is from the star the less light rays would hit it.

]]> By: peted66616 http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550538 peted66616 Sat, 06 Oct 2012 18:38:00 +0000 http://boingboing.net/?p=185596#comment-1550538 Right. Like I said, raises more questions than it answers. I.e. it's well and good for you or someone else to be able to explain these things, but the video does not. Right. Like I said, raises more questions than it answers.

I.e. it’s well and good for you or someone else to be able to explain these things, but the video does not.

]]> By: Sarah Mavity http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550534 Sarah Mavity Sat, 06 Oct 2012 18:24:00 +0000 http://boingboing.net/?p=185596#comment-1550534 im so confused... im so confused…

]]> By: desiredusername http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550513 desiredusername Sat, 06 Oct 2012 17:22:00 +0000 http://boingboing.net/?p=185596#comment-1550513 No its that the sun is the center of the universe. No its that the sun is the center of the universe.

]]> By: vinho http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550491 vinho Sat, 06 Oct 2012 16:29:00 +0000 http://boingboing.net/?p=185596#comment-1550491 If light hasn't reached us yet how could telescopes that are just magnifying from where we are see it earlier? If light hasn’t reached us yet how could telescopes that are just magnifying from where we are see it earlier?

]]> By: KeithIrwin http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550470 KeithIrwin Sat, 06 Oct 2012 15:45:00 +0000 http://boingboing.net/?p=185596#comment-1550470  It doesn't say that there's an infinite number of stars because there aren't.  It just says that the universe doesn't have an edge.  If you were a two-dimensional being walking on the surface of a very large sphere, you'd never find an end of it, but it would still be finite.  We're three dimensional beings in a bounded universe, but if we can move through it as much as we want and will never find an edge.  It's just assuming that there's enough stars that it should fill the sky.  I'm not sure that's justified given distance and spread.  It is true that there is energy coming from all directions because some of it came from the time of the big bang when everything was more densely packed, but I'm not sure that energy is very bright.  I did some web searches to try to answer that, but didn't have any luck. About the red-shift, there is an upper limit to how energetic photons produced by stars are.  For distant enough galaxies, the red-shift is sufficient to shift all of the photons below the visible range.  For example, when we look for light emitted very near the time of the big bang (and thus currently coming from very far away), we use telescopes capable of seeing microwaves, which is a range whose frequency is below the range of visible light.  It doesn’t say that there’s an infinite number of stars because there aren’t.  It just says that the universe doesn’t have an edge.  If you were a two-dimensional being walking on the surface of a very large sphere, you’d never find an end of it, but it would still be finite.  We’re three dimensional beings in a bounded universe, but if we can move through it as much as we want and will never find an edge.  It’s just assuming that there’s enough stars that it should fill the sky.  I’m not sure that’s justified given distance and spread.  It is true that there is energy coming from all directions because some of it came from the time of the big bang when everything was more densely packed, but I’m not sure that energy is very bright.  I did some web searches to try to answer that, but didn’t have any luck.

About the red-shift, there is an upper limit to how energetic photons produced by stars are.  For distant enough galaxies, the red-shift is sufficient to shift all of the photons below the visible range.  For example, when we look for light emitted very near the time of the big bang (and thus currently coming from very far away), we use telescopes capable of seeing microwaves, which is a range whose frequency is below the range of visible light.

]]> By: KeithIrwin http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550460 KeithIrwin Sat, 06 Oct 2012 15:20:00 +0000 http://boingboing.net/?p=185596#comment-1550460 This video is factually incorrect about the cause of the red shift.  It is not caused by the doppler effect, it is caused by the space the photons are moving through expanding, thus lowering their wavelengths.  Distant galaxies are not moving away from us.  They are hardly moving.  We are also hardly moving.  But we are getting farther apart from them because the universe is expanding.  This is the cause of the redshift.  It is called Cosmological redshift.  The wikipedia description is reasonable. https://en.wikipedia.org/wiki/Redshift#Expansion_of_space This video is factually incorrect about the cause of the red shift.  It is not caused by the doppler effect, it is caused by the space the photons are moving through expanding, thus lowering their wavelengths.  Distant galaxies are not moving away from us.  They are hardly moving.  We are also hardly moving.  But we are getting farther apart from them because the universe is expanding.  This is the cause of the redshift.  It is called Cosmological redshift.  The wikipedia description is reasonable. https://en.wikipedia.org/wiki/Redshift#Expansion_of_space

]]> By: bcsizemo http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550440 bcsizemo Sat, 06 Oct 2012 14:34:00 +0000 http://boingboing.net/?p=185596#comment-1550440 So the answer is the fact there is no visible spectrum light for us to see...umm isn't that what "darkness" is to most people?  I mean from a science standpoint just because something is dark or black doesn't mean there isn't radiation/energy present, but to the average person sitting in a pitch black room there is just no light (ie they don't make the distinction that there might be an infrared energy source, thus providing some type of energy input, just they know there isn't anything they can see.) So when the kids ask why the sky is black at night, the realistically correct answer is there is no "light" (at least in the visible term). So the answer is the fact there is no visible spectrum light for us to see…umm isn’t that what “darkness” is to most people?  I mean from a science standpoint just because something is dark or black doesn’t mean there isn’t radiation/energy present, but to the average person sitting in a pitch black room there is just no light (ie they don’t make the distinction that there might be an infrared energy source, thus providing some type of energy input, just they know there isn’t anything they can see.)

So when the kids ask why the sky is black at night, the realistically correct answer is there is no “light” (at least in the visible term).

]]> By: Guest http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550427 Guest Sat, 06 Oct 2012 14:08:00 +0000 http://boingboing.net/?p=185596#comment-1550427 deleted deleted

]]> By: zotlerg http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550411 zotlerg Sat, 06 Oct 2012 12:57:00 +0000 http://boingboing.net/?p=185596#comment-1550411 The sky is blue during the day because the sun's light is brighter than the stars, and it's light is scattered like a bright light placed in the sea at night. : ) The sky is blue during the day because the sun’s light is brighter than the stars, and it’s light is scattered like a bright light placed in the sea at night. : )

]]> By: IamInnocent http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550400 IamInnocent Sat, 06 Oct 2012 11:19:00 +0000 http://boingboing.net/?p=185596#comment-1550400  Accuracy is much tougher on the brain. Ouch!  Accuracy is much tougher on the brain. Ouch!

]]> By: Antinous / Moderator http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550390 Antinous / Moderator Sat, 06 Oct 2012 09:59:00 +0000 http://boingboing.net/?p=185596#comment-1550390 Or Arien was screwing around that day and didn't have her fruit turned all the way up. Or Arien was screwing around that day and didn’t have her fruit turned all the way up.

]]> By: stephenl123 http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550385 stephenl123 Sat, 06 Oct 2012 09:17:00 +0000 http://boingboing.net/?p=185596#comment-1550385 Also in the case of Orfalch Echor there's the possibility that a flat Earth coincided with more visible stars of the first magnitude. Also in the case of Orfalch Echor there’s the possibility that a flat Earth coincided with more visible stars of the first magnitude.

]]> By: stephenl123 http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550382 stephenl123 Sat, 06 Oct 2012 09:05:00 +0000 http://boingboing.net/?p=185596#comment-1550382 Perhaps the narrow field of view can make it appear that the few bright stars visible from those locations are a sky full of stars, if by chance several stars of the first magnitude are in the field of view?  http://www.4information.com/trivia/stars-daytime-well/ Perhaps the narrow field of view can make it appear that the few bright stars visible from those locations are a sky full of stars, if by chance several stars of the first magnitude are in the field of view?  http://www.4information.com/trivia/stars-daytime-well/

]]> By: Antinous / Moderator http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550367 Antinous / Moderator Sat, 06 Oct 2012 07:05:00 +0000 http://boingboing.net/?p=185596#comment-1550367 Why is it that, if you're just on your way out of the Paths of the Dead or hanging out in the Orfalch Echor, you can see stars even in the middle of the day? Why is it that, if you’re just on your way out of the Paths of the Dead or hanging out in the Orfalch Echor, you can see stars even in the middle of the day?

]]> By: Antinous / Moderator http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550363 Antinous / Moderator Sat, 06 Oct 2012 06:53:00 +0000 http://boingboing.net/?p=185596#comment-1550363 I can ask, but nobody ever seems to know the answer to that sort of question. I can ask, but nobody ever seems to know the answer to that sort of question.

]]> By: Phanatic http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550360 Phanatic Sat, 06 Oct 2012 06:51:00 +0000 http://boingboing.net/?p=185596#comment-1550360 The light from all the stars in the Universe does reflect and scatter off our atmosphere producing a blue sky, all the time.  If you set out a camera and set the exposure properly, then you will get a blue sky.  This is most easily seen when there's significant moonlight, demonstrating that the Rayleigh scattering that results in the sky appearing blue during the daytime is every bit as active with the smaller amount of incoming light we receive during the night.  If your eye integrated like a camera does, you'd see blue skies.  Here's a 13-minute exposure.  Looks blue to me.  Also note how the foreground looks like it's illuminated by sunlight. Because it is, just much less of it than during the day. http://www.coe.montana.edu/ee/jshaw/publications/Blue_Night_Sky_OPN1996/bluesky1_mod.jpg The light from all the stars in the Universe does reflect and scatter off our atmosphere producing a blue sky, all the time.  If you set out a camera and set the exposure properly, then you will get a blue sky.  This is most easily seen when there’s significant moonlight, demonstrating that the Rayleigh scattering that results in the sky appearing blue during the daytime is every bit as active with the smaller amount of incoming light we receive during the night.  If your eye integrated like a camera does, you’d see blue skies. 

Here’s a 13-minute exposure.  Looks blue to me.  Also note how the foreground looks like it’s illuminated by sunlight. Because it is, just much less of it than during the day.
http://www.coe.montana.edu/ee/jshaw/publications/Blue_Night_Sky_OPN1996/bluesky1_mod.jpg

]]> By: KBert http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550327 KBert Sat, 06 Oct 2012 05:02:00 +0000 http://boingboing.net/?p=185596#comment-1550327  Thanks for the follow up... Looking about WP support forums for the answer, maybe a plugin adjustment by BB might allow us a profile pic w/o dealing with Disqus?  Thanks for the follow up… Looking about WP support forums for the answer, maybe a plugin adjustment by BB might allow us a profile pic w/o dealing with Disqus?

]]> By: Boundegar http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550328 Boundegar Sat, 06 Oct 2012 05:02:00 +0000 http://boingboing.net/?p=185596#comment-1550328 That would offend my fragile masculinity. That would offend my fragile masculinity.

]]> By: Boundegar http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550326 Boundegar Sat, 06 Oct 2012 05:00:00 +0000 http://boingboing.net/?p=185596#comment-1550326 That's interesting - according to the wiki, every possible explanation has been dismissed.  However, I will point out that Genesis 1 only mentions two lights in the sky.  Therefore, stars do not exist. That’s interesting – according to the wiki, every possible explanation has been dismissed.  However, I will point out that Genesis 1 only mentions two lights in the sky.  Therefore, stars do not exist.

]]> By: Antinous / Moderator http://boingboing.net/2012/10/05/why-is-the-sky-dark-at-night.html#comment-1550323 Antinous / Moderator Sat, 06 Oct 2012 04:46:00 +0000 http://boingboing.net/?p=185596#comment-1550323 It looks like the profile pic is only a Disqus feature, not a WP feature. I guess that you can't change it unless you create a Disqus account. Sorry. I had suggested at one point that we change the default avatar to Jill, but nobody ever got a round to it. It looks like the profile pic is only a Disqus feature, not a WP feature. I guess that you can’t change it unless you create a Disqus account. Sorry. I had suggested at one point that we change the default avatar to Jill, but nobody ever got a round to it.

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