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1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 8:07 am UTC
by Ekaros
Image

Alt-text:
'The light from those millions of stars you see is probably many thousands of years old' is a rare example of laypeople substantially OVERestimating astronomical numbers.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 8:20 am UTC
by tsadi
Boy: Or it could have gone supernova already?
Girl: Nope, it doesn't have enough mass to do that either.
Boy: Wanna make out?

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 8:26 am UTC
by rhomboidal
Hehe, I wasn't aware there was ANY light emitted in the previous presidential administration.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 8:51 am UTC
by Djehutynakht
Yeah... I've seen some sort of meme related to this going around on the internet. I assume Randall refers to this.

Sure, some are dead. Many aren't. Stars last for billions of years.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:06 am UTC
by snowyowl
Yes, but the light from that galaxy was emitted two million years ago. Admittedly it's a bit hard to see it with the naked eye - look for the constellation Andromeda, and it's a fuzzy patch next to her knee. Still romantic if you can find it.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:45 am UTC
by orthogon
The thing is, the stars are ridiculously far away, but light travels stupidly fast, so dividing one by the other it's not obvious whether you'll get a big number or a small one.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:50 am UTC
by time burglar
OK, now I want a picture of the night sky that somehow (colour scale?) shows how many light years away each star is. Rather over-optimistically, I had hoped the mouseover text would show me that :(

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:52 am UTC
by Diadem
orthogon wrote:The thing is, the stars are ridiculously far away, but light travels stupidly fast, so dividing one by the other it's not obvious whether you'll get a big number or a small one.

Yup. Astronomy is all about dividing the ridiculous by the stupid. Unlike astrology, which is about adding the ridiculous and the stupid :)

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 10:32 am UTC
by PinkShinyRose
Diadem wrote:
orthogon wrote:The thing is, the stars are ridiculously far away, but light travels stupidly fast, so dividing one by the other it's not obvious whether you'll get a big number or a small one.

Yup. Astronomy is all about dividing the ridiculous by the stupid. Unlike astrology, which is about adding the ridiculous and the stupid :)

I think astrology is actually rather complicated, ridiculous, but I don't think the stupid would do it "right".

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 11:23 am UTC
by Red Hal
time burglar wrote:OK, now I want a picture of the night sky that somehow (colour scale?) shows how many light years away each star is. Rather over-optimistically, I had hoped the mouseover text would show me that :(
best I can do is link this: http://www.atlasoftheuniverse.com/50lys.html

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 11:28 am UTC
by Klear
Diadem wrote:
orthogon wrote:The thing is, the stars are ridiculously far away, but light travels stupidly fast, so dividing one by the other it's not obvious whether you'll get a big number or a small one.

Yup. Astronomy is all about dividing the ridiculous by the stupid. Unlike astrology, which is about adding the ridiculous and the stupid :)

I call astrology the exact pseudoscience.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 1:01 pm UTC
by rmsgrey
Taking the 1400 systems within 50 LY figure and extrapolating up to 1000 LY, that gives 8000 times as many systems, or about 10 000 000 stars. So the million brightest (by apparent magnitude) stars in the sky are probably mostly within 1000 LY - on the other hand, if you can see over a million different stars, it's a reasonable estimate to say that the light from some of them is going to be about a thousand years old.

On the other hand, there are only about 10 000 stars visible to the naked eye, so both the millions and the many thousands are indeed substantial overestimates.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 1:08 pm UTC
by drachefly
rmsgrey wrote:Taking the 1400 systems within 50 LY figure and extrapolating up to 1000 LY, that gives 8000 times as many systems, or about 10 000 000 stars. So the million brightest (by apparent magnitude) stars in the sky are probably mostly within 1000 LY


Does not follow. Red dwarfs are so much commoner and dimmer than other stars that I really wouldn't count on that.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 1:27 pm UTC
by Jackpot777
Diadem wrote:
orthogon wrote:The thing is, the stars are ridiculously far away, but light travels stupidly fast, so dividing one by the other it's not obvious whether you'll get a big number or a small one.

Yup. Astronomy is all about dividing the ridiculous by the stupid. Unlike astrology, which is about adding the ridiculous and the stupid :)


I have to stop and mentally check myself (before I wreck myself? Maybe) when it comes to local star distribution. In the sun's immediate neighborhood, there's about 1 star for every 284 cubic light years. That sounds like a lot of space between stars considering Proxima Centauri is around 4.2 light years distant, but a cube with sides of 6 l.y is 216 cubic light years. 7 l.y cubed is 343 cubic light years.

When I start cubing numbers, they don't feel like they're right. The answers seem too big.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 1:34 pm UTC
by Jackpot777
rmsgrey wrote:Taking the 1400 systems within 50 LY figure and extrapolating up to 1000 LY, that gives 8000 times as many systems, or about 10 000 000 stars. So the million brightest (by apparent magnitude) stars in the sky are probably mostly within 1000 LY - on the other hand, if you can see over a million different stars, it's a reasonable estimate to say that the light from some of them is going to be about a thousand years old.

On the other hand, there are only about 10 000 stars visible to the naked eye, so both the millions and the many thousands are indeed substantial overestimates.


I was just talking about this on Reddit yesterday. Ended up doing an ad-hoc Drake Equation calculation using a lot of assumption, the Cosmic Calendar, and estimates as to how long a civilization would transmit radio waves.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 3:08 pm UTC
by keithl
1) For some people, the delay from the stars is more than 1000 years, if you include the time it takes for a new idea about the nature of the universe to penetrate their brains. :?

2) Most Fermi Paradox musings are adequately explained by the economic discount rate and the speed of light - value in the future is worth less than value now, and stars are distant in human time. This puts a horizon on how far away a production center expecting a return on investment (like "we made it") will send expensive, decaying assets. Less than 250 years even with "exponentially" generous assumptions, probably much less than that. A 500 ly diameter collection of Dyson-shelled stars would be exceedingly hard to detect at trans-galactic distances, and conversation would be pointless. See http://server-sky.com/WhereAreThey

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 3:21 pm UTC
by San Fran Sam
Diadem wrote:
orthogon wrote:The thing is, the stars are ridiculously far away, but light travels stupidly fast, so dividing one by the other it's not obvious whether you'll get a big number or a small one.

Yup. Astronomy is all about dividing the ridiculous by the stupid. Unlike astrology, which is about adding the ridiculous and the stupid :)


Or politics which is the ridiculous multiplied by the stupid.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 3:41 pm UTC
by Wooloomooloo
The point this comic makes is an interesting one, but I find it exceedingly hard to agree with the sentiment /conclusion. FFS, the Milky Way alone is 100Kly in diameter, and other galaxies MILLIONS of ly away are visible with the naked eye! Sure, the odds of the first thing you see up there being within 1Kly might be really good but come on... it just does not follow that the original assertion can be blanket-shunned...!

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 3:52 pm UTC
by Whizbang
Wait.

So, we're constantly told how HUGE the universe is. How OLD it is. How MANY stars and planets there are. How You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space... And then you turn around and tell us (laypeople) that it is silly to say how the light from all (read most) those stars are thousands of years old?

This reminds me of that one time we were told over and over again in elementary schoole that Columbus discovered America, then tell us in Junior High that that's not, technically, true. Or that other time when they said the dinosaurs died out millions of years ago, then then told us that birds are really just a few evolutionary steps away from them.

I call rule 1053 on this comic.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 4:18 pm UTC
by Sprocket
I think the misunderstanding is mostly about really getting how fast light travels.

Whizbang wrote:This reminds me of that one time we were told over and over again in elementary schoole that Columbus discovered America, then tell us in Junior High that that's not, technically, true.

I reference this all the damn time.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 4:18 pm UTC
by chenille
For those wondering, taking the stars down to magnitude 3, 4, or 4½ all give median distances of about 200 light-years; down to 5 is maybe a bit more but involves too many really faint stars for me to bother. The mean would be harder to work out because the distances to the furthest stars aren't as well known, like Deneb, which is one of the several dozen more than a thousand away. Nothing much seems to be anywhere close to ten thousand light-years.

None of this is dim enough yet to consider stars that will live billions of years, they're almost all larger or much larger than the sun. The brighter constellations you see are all relatively temporary, full of stars that would not just have been in different places but would not even have been born when dinosaurs first roamed the earth. But as you see, that's a long time compared to how fast light travels.

If it's a dark night and you want to see something genuinely far away, though, as snowyowl says there's always the Andromeda galaxy; the light from that is older than the first Homo habilis fossils. Not much chance it's gone away in the mean time, though.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 4:23 pm UTC
by hercynium
I think he passed up an excellent opportunity for the alt-text...

"Surely that can't be Sirius?"
"It is serious, and stop calling me Shirley."

:wink:

(I told this, and another stupid thought about this comic to a cow-orker. She told me I should sent it to Randall, but, being a conscientious netizen, I checked the "Contact" section on the site which suggests comments be posted here or on IRC... So now you are all subjected to my inanity *mwahahah*)

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 4:38 pm UTC
by hercynium
Also, my second thought was a puzzle, belaboring a bad pun in a nerdy way and not at all funny unless you're amused by the same weird things as I...

Today's comic made me realize that the earth will be toast sometime around Feb 12, 2026 (± 1 month or so due to various reasons), and there's nothing we can do about it because we caused it starting sometime around Dec 1, 2008 (maybe sooner, uncertainty due to incomplete data).

The question: What happened?

Hint #1: Sirius is also known as "The Dog Star"

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 4:47 pm UTC
by eran_rathan
San Fran Sam wrote:
Diadem wrote:
orthogon wrote:The thing is, the stars are ridiculously far away, but light travels stupidly fast, so dividing one by the other it's not obvious whether you'll get a big number or a small one.

Yup. Astronomy is all about dividing the ridiculous by the stupid. Unlike astrology, which is about adding the ridiculous and the stupid :)


Or politics which is the ridiculous multiplied by the stupid.


I'd have called it stupid exponented by the ridiculous.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 5:27 pm UTC
by Wnderer
800px-Star-sizes.jpg


Okay I was looking up the distances to the stars (most of the ones in Orion are around 100 to 1000 light years away so 8 is misleadingly small). Anyway, I'm easily distracted. This picture is really really cool.

http://en.wikipedia.org/wiki/File:Star-sizes.jpg

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 6:22 pm UTC
by Earthling on Mars
hercynium wrote:Today's comic made me realize that the earth will be toast sometime around Feb 12, 2026 (± 1 month or so due to various reasons), and there's nothing we can do about it because we caused it starting sometime around Dec 1, 2008 (maybe sooner, uncertainty due to incomplete data).

The question: What happened?

Hint #1: Sirius is also known as "The Dog Star"

I suppose it's only natural that the dogs would want to defend their smaller oppressed kinfolk. Though I think the trouble actually started in 2006. (That is, if I guessed your riddle right, which I'm not completely sure of...)

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 6:30 pm UTC
by pitareio
Wnderer wrote:
800px-Star-sizes.jpg


Okay I was looking up the distances to the stars (most of the ones in Orion are around 100 to 1000 light years away so 8 is misleadingly small). Anyway, I'm easily distracted. This picture is really really cool.

http://en.wikipedia.org/wiki/File:Star-sizes.jpg


Something to keep you distracted a little longer : http://joshworth.com/dev/pixelspace/pix ... ystem.html

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 8:35 pm UTC
by Paulmichael
Actually, given that the light to leave even our own sun is, on average, thousands of years old (NASA) when it finally escapes the star, all light we see from distant stars is technically thousands of years old (though the stars that we can see with the naked eye are likely still there).

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:05 pm UTC
by ucim
Paulmichael wrote:Actually, given that the light to leave even our own sun is, on average, thousands of years old (NASA) when it finally escapes the star...
Yes, but after all that bouncing around, are they still really the "same" photons?

Jose

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:05 pm UTC
by Ekaros
Aren't most of the stars on the sky we can separate from each other around us and quite near and on other hand those that are farther away are in plane of galaxy and thus we don't really distinguish them from each other...
Though I know very little of astronomy...

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:32 pm UTC
by hercynium
Earthling on Mars wrote:
hercynium wrote:Today's comic made me realize that the earth will be toast sometime around Feb 12, 2026 (± 1 month or so due to various reasons), and there's nothing we can do about it because we caused it starting sometime around Dec 1, 2008 (maybe sooner, uncertainty due to incomplete data).

The question: What happened?

Hint #1: Sirius is also known as "The Dog Star"

I suppose it's only natural that the dogs would want to defend their smaller oppressed kinfolk. Though I think the trouble actually started in 2006. (That is, if I guessed your riddle right, which I'm not completely sure of...)


I should have come back to post more hints like I did on facebook, but I didn't so here's the answer:

Spoiler:
On 2008-12-01, Florence + The Machine released the single "Dog Days Are Over".
It received heavy airplay in Great Britain but did not reach worldwide popularity
for over a year.

Eight-point-six years later (Earth time) the signal of these broadcast transmissions
reached Sirius. Upon hearing of its loss of purpose and relevancy it promptly and
unexpectedly exploded.

Earth, of course, did not know this had happened for another 8.6 years, in early
2026, when the first waves of radiation hit. Due to the supernova's proximity, it
burned our planet to a cinder, ironically bringing about the fiery cataclysm the
star believed it had failed to fulfill years before.


(a reminder: I did say this is horribly un-funny...) :roll:

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 9:34 pm UTC
by Paulmichael
ucim wrote:
Paulmichael wrote:Actually, given that the light to leave even our own sun is, on average, thousands of years old (NASA) when it finally escapes the star...
Yes, but after all that bouncing around, are they still really the "same" photons?

Jose


Well, I imagine that what we consider to be light that is bright enough to be seen from a star is a cluster of many billions of photons, and at least a few of those photons are likely to be thousands of years "old." Not being an astrophysicist, I have no actual idea. :lol:

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 10:26 pm UTC
by Existentialism
I registered on these forums just to posit that the person on the right is Michio Kaku. That is all.

Re: 1342: "Ancient Stars"

Posted: Fri Mar 14, 2014 11:57 pm UTC
by Klear
Paulmichael wrote:
ucim wrote:
Paulmichael wrote:Actually, given that the light to leave even our own sun is, on average, thousands of years old (NASA) when it finally escapes the star...
Yes, but after all that bouncing around, are they still really the "same" photons?

Jose


Well, I imagine that what we consider to be light that is bright enough to be seen from a star is a cluster of many billions of photons, and at least a few of those photons are likely to be thousands of years "old." Not being an astrophysicist, I have no actual idea. :lol:


I believe I read that since they travel at c, photons actually don't age at all...

Re: 1342: "Ancient Stars"

Posted: Sat Mar 15, 2014 1:12 am UTC
by cronjob
Light is a form of electromagnetic radiation. Radiation defines motion. Light does not move as does the arrow to the tree. It radiates. The motion of a photon consists of bumping into another photon. In this way, information is passed from one photon to another. But what are the odds that a single photon would come all the way from Andromeda and actually strike the surface of the eye ball of someone standing here on Earth?

Earth, being so close to the Sun to begin with, is completely and totally awash in local photons, and has been for quite sometime. So, I would think that almost every photon that strikes the surface of your eye was in fact emitted by our Sun (Sol). So, how does the eye (or the human being it's attached to) make sense of or, create an image of, electromagnetic radiation that radiated information through a process of bumping it along from one photon to the next?

p.s. I find this concept to be quite fascinating so, please don't prove me wrong. I want to know how the actual information arrives by way of radiation to the surface of the eye.

Re: 1342: "Ancient Stars"

Posted: Sat Mar 15, 2014 1:24 am UTC
by Xenomortis
cronjob wrote:The motion of a photon consists of bumping into another photon.

Erm... no.
Photons are not some medium for wave propagation, photons are the propagation.
cronjob wrote:I want to know how the actual information arrives by way of radiation to the surface of the eye.

Star emits photon.
Photon travels through space.
Photon hits eye.

Re: 1342: "Ancient Stars"

Posted: Sat Mar 15, 2014 3:38 am UTC
by cronjob
Xenomortis wrote:
cronjob wrote:The motion of a photon consists of bumping into another photon.

Erm... no.
Photons are not some medium for wave propagation, photons are the propagation.


Electromagnetic radiation is pure energy with no mass. This covers the entire spectrum. Both visible and non-visible.
Electromagnetic radiation actually consists of vibrating/pulsating waves of electrical and magnetic energy. Additionally, electromagnetic radiation can be thought of as a stream of packets of energy. These packets of massless energy are called photons. Each photon particle still "travels" in a wave form type of pattern. Each photon has a certain amount of energy. All electromagnetic radiation consists of photons. The only thing that is different from one type of electromagnetic radiation to the next is the amount of energy contained within the actual photons themselves.

This much I already know.

I also know that electromagnetic radiation travels in a straight line at the speed of light (3 x 108 m/s). And yet packets collide. They radiate. This is how they move and they exchange information when they collide. This much I already know.

I also know that from the day we are born until the day we die, almost every single photon that strikes the surfaces of our eyes is local due to Earths proximity to something the called the Sun. To see Andromeda, those photons have to wade through the overwhelming amount of photons that our entire solar system has been bathing in since our own star went online 4.5 billion years ago. Photons must therefor be able to pass on "information" (of a kind) when they collide, for us to see Andromeda.

So, while the idea of a single photon traveling 250 million light years just to be absorbed by the human eye may seem like a romantic notion to some, that's not actually how it works.

p.s. I still want to know if anybody out there does know and can explain it to the unwashed among us...

Re: 1342: "Ancient Stars"

Posted: Sat Mar 15, 2014 3:43 am UTC
by rmsgrey
cronjob wrote:Light is a form of electromagnetic radiation. Radiation defines motion. Light does not move as does the arrow to the tree. It radiates. The motion of a photon consists of bumping into another photon. In this way, information is passed from one photon to another. But what are the odds that a single photon would come all the way from Andromeda and actually strike the surface of the eye ball of someone standing here on Earth?

Earth, being so close to the Sun to begin with, is completely and totally awash in local photons, and has been for quite sometime. So, I would think that almost every photon that strikes the surface of your eye was in fact emitted by our Sun (Sol). So, how does the eye (or the human being it's attached to) make sense of or, create an image of, electromagnetic radiation that radiated information through a process of bumping it along from one photon to the next?

p.s. I find this concept to be quite fascinating so, please don't prove me wrong. I want to know how the actual information arrives by way of radiation to the surface of the eye.


Photons don't bump into each other - in fact, they don't interact with each other at all - if you have two photons on a collision course, they just pass through each other without noticing. What stops a photon is encountering a charged particle (or a magnetic monopole if they exist) - and only if the particle can absorb all of the photon's energy. When astrophysicists say that a photon takes thousands of years to escape the Sun, what they actually mean is that the original photon gets absorbed by a charged particle, which then emits another, similar photon in an unpredictable direction some time later, and if you follow the energy, then it takes thousands of years and trillions of collisions for that original bit of energy to be wrapped up as a photon that's leaving the Sun...

Re: 1342: "Ancient Stars"

Posted: Sat Mar 15, 2014 3:52 am UTC
by Mikeski
San Fran Sam wrote:Or politics which is the ridiculous multiplied elected by the stupid.

Fixed.

Re: 1342: "Ancient Stars"

Posted: Sat Mar 15, 2014 4:27 am UTC
by cronjob
hercynium wrote:
Earthling on Mars wrote:
hercynium wrote:Today's comic made me realize that the earth will be toast sometime around Feb 12, 2026 (± 1 month or so due to various reasons), and there's nothing we can do about it because we caused it starting sometime around Dec 1, 2008 (maybe sooner, uncertainty due to incomplete data).

The question: What happened?

Hint #1: Sirius is also known as "The Dog Star"

I suppose it's only natural that the dogs would want to defend their smaller oppressed kinfolk. Though I think the trouble actually started in 2006. (That is, if I guessed your riddle right, which I'm not completely sure of...)


I should have come back to post more hints like I did on facebook, but I didn't so here's the answer:

Spoiler:
On 2008-12-01, Florence + The Machine released the single "Dog Days Are Over".
It received heavy airplay in Great Britain but did not reach worldwide popularity
for over a year.

Eight-point-six years later (Earth time) the signal of these broadcast transmissions
reached Sirius. Upon hearing of its loss of purpose and relevancy it promptly and
unexpectedly exploded.

Earth, of course, did not know this had happened for another 8.6 years, in early
2026, when the first waves of radiation hit. Due to the supernova's proximity, it
burned our planet to a cinder, ironically bringing about the fiery cataclysm the
star believed it had failed to fulfill years before.


(a reminder: I did say this is horribly un-funny...) :roll:


I think that was a worthy effort. Maybe not what I would call a "knee slapper" but, hey you tried. That's gotta count for something.

...about those radio waves though...
http://zidbits.com/2011/07/how-far-have ... rom-earth/

Here I am quoting from the above link:

"As radio signals leave earth, they propagate out in a wave form. Just like dropping a stone in a lake, the waves diffuse or “spread out” over distance thanks to the exponentially larger area they must encompass. The area can be calculated by multiplying length times width which is why we measure it in square units – square centimeters, square miles, etc. This means that the further away from the source, the more square units of area a signal has to ‘illuminate’.inverse square law

Another way to think of it, is that the strength of a radio signal will be only 1/4 as great once you are twice the distance from the source. At ten times the distance, the strength of the signal would only be one hundredth as great.

Because of this inverse square law, all of our terrestrial radio signals become indistinguishable from background noise at around a few light-years from earth. For a civilization only a couple hundred light-years away, trying to listen to our broadcasts would be like trying to detect the small ripple from a pebble dropped in the pacific ocean off the coast of California – from Japan."

...nice try though. :mrgreen: