DaveC426913
Valued Senior Member
Light years?
- Thread starter wegs
- Start date
Yes.
I'm certain that others here can offer far better recommendations, but I always thought Heinz Pagels' Cosmic Code <<< was an excellent introductory text to all such matters, which mostly omits all the pesky, pain-in-the-ass math shit--and I think it was fairly highly regarded by those who ostensibly know this stuff. (I dunno, is that still the case?). And it's a good read: it's not dry and, while conveying difficult concepts, it's not gonna have you pulling your hair out--I mean, I think I first read it when I was like 14 or 15, so...
Lol!!
This is one of those “explain like I’m five” scenarios. So…since posting this thread, I asked one of my neighbors, “do you know what a light year is?” They knew, but didn’t explain it well. Same with two of my coworkers. Thanks to some of you, I paid it forward and they too can experience the wonder.
I’m going to ask random people soon enough lol
Not dry. Leaves out the math. I’m in!
In high school and to some extent colllege, it felt like if you didn’t understand the concepts right away or weren’t a math whiz (at least with the profs I was stuck with) you were a bit lost because my teachers seemed more interested in lecturing, than teaching. I can’t help but think that many who work at NASA for example, probably had great teachers who got them excited about science.
Better late than never though, right?
Lol!!
This is one of those “explain like I’m five” scenarios. So…since posting this thread, I asked one of my neighbors, “do you know what a light year is?” They knew, but didn’t explain it well. Same with two of my coworkers. Thanks to some of you, I paid it forward and they too can experience the wonder.
All other things aside, any discussion of light speed and light years and whatnots necessarily, and tangentially, touches upon one of my pet obsessions: matters of numeracy and number sense (well, to be specific, across species--but that's way too much a digression and I don't want Dave to lose it.). I mean, regardless the unit of measurement--unless we just use "light years" and leave it at that--these discussions necessarily involve billions and trillions and beyond of things.
And, seriously, what does "a billion" mean to you? To me, frankly, it doesn't mean shit--I mean, not in any real or practical sense. I can't really fathom a billion of anything.
Anyways, that's kind of a needless digression, but I don't think it wholly irrelevant to really grasping such matters.
Not dry. Leaves out the math. I’m in!
In high school and to some extent colllege, it felt like if you didn’t understand the concepts right away or weren’t a math whiz (at least with the profs I was stuck with) you were a bit lost because my teachers seemed more interested in lecturing, than teaching. I can’t help but think that many who work at NASA for example, probably had great teachers who got them excited about science.
Better late than never though, right?
Just out of curiosity, when you were really young did you learn--memorize, rather--multiplication tables and suchlike? Apparently, in the US and Canada at least, they don't do that stuff anymore, and I think that's a really bad idea. I'm not entirely sure when such was abandoned however. Sure, rote memorization can only get one so far, but it's also not completely useless.
Yes, I did…but if you don’t know why you’re learning something (I’m one of those that likes to know why, even now) it can disrupt learning (fully grasping) those subjects on a deeper level.
I think it’s important to know why scientists use light years as a form of measurement for example, just as much as learning what a light year is.
to add to the confusion, "our" billion used to be bigger than the US billion before "till the pips squeak" Chancellor Dennis Healey abandoned British metrical independence in 1975
We used to say it was a million times a million.Alas no more -just the paltry thousand times a million.
https://www.theguardian.com/notesandqueries/query/0,5753,-61424,00.html
(only took me 47 years to get with the times)
We used to say it was a million times a million.Alas no more -just the paltry thousand times a million.
https://www.theguardian.com/notesandqueries/query/0,5753,-61424,00.html
(only took me 47 years to get with the times)
So, light that is emitted from remote galaxies, that reaches us would have to be “redshifted” for us to see it? (Because the universe is expanding, the wavelengths would become “longer” in order for us to see.)
Could there be any other reason that it could be red, besides distance?
Could there be any other reason that it could be red, besides distance?
DaveC426913
Valued Senior Member
On very large scales that is what we observe.
Two things of note:
- the effect is too small to affect gravitationally-bound objects - even other galaxies in our local cluster are gravitationally bound enough to not be affected by Cosmological Expansion
- the expansion is an average. Galaxies still have their own intrinsic velocities. Andromeda, for example - The Milky Way's next door neighbour - is actually hurtling toward us, so it is blue-shifted.
Plenty of theories. None of them as strong as Cosmological Expansion. ("tired light" is one such competitor.)
It will take four billion years to “merge” with the Milky Way; I guess that’s considered “hurtling” in science. lol
Apparently, it’s considered a fringe theory.
When I was a kid, I was initially confused in reading science books. It took me a while to work out that the British ones used a different billion than the US ones. Eventually, it seems that everybody caved in to US influence on this, which at least eliminated some confusion.to add to the confusion, "our" billion used to be bigger than the US billion before "till the pips squeak" Chancellor Dennis Healey abandoned British metrical independence in 1975
We used to say it was a million times a million.Alas no more -just the paltry thousand times a million.
Here's how things used to work:
In the US:
1 million = 1 000 000
1 billion = 1 000 000 000
1 trillion = 1 000 000 000 000
Most other places:
1 million = 1 000 000
1 thousand million = 1 000 000 000
1 billion = 1 million million = 1 000 000 000 000
1 trillion = 1 million million million = 1 000 000 000 000 000 000 (or maybe 1 billion billion? = 1 000 000 000 000 000 000 000 000. Not sure about this one, but logically this would make more sense.)
Yes.
First, red shifting can be caused by any relative motion, not just relative motion due to the expansion of space. Things that are moving towards us - for whatever reason - will emit light that is blue shifted when it reaches us; things that are moving away emit light that ends up red shifted. It turns out that, outside our own galaxy, the vast majority of things we can see have red shifts, because the large-scale expansion of the universe has the largest effect on their relative motion. There are a few galaxies in our local group that show blue shifts, but the number can be counted on one hand, practically.
Second, light propagating through matter can pick up a red tint, because smaller wavelengths (e.g. blue or green light) tend to be scattered more than red. For example, light from a distant star that has to pass through interstellar gas clouds to reach us, often ends up looking redder than when it was emitted, because the blue and green components of the light don't reach us on Earth (or, at least, not as much, relative to red).
This second reason is why the new James Webb Space Telescope is designed to use infrared light, which is scattered and absorbed by even less than visible red light by gas and dust. That means that the JWST can see things that were invisible to Hubble (which worked in visible light).
Thanks, James. Something I'm confused on - so, light isn't always traveling freely through space. There can be blockage from dust, rocks, etc...so, that light from certain distant stars for example, may never reach us, but does the expansion of the universe have a speed?
DaveC426913
Valued Senior Member
Yes.
The rate is about 45 miles per second per Megaparsec. A parsec is about 3.25 light years.
That means things that are about 3.25 million light years away are receding at 45 miles per second, whereas things that are about 32.5 million light years away are receding at 450 miles per second.
Very simply, mostly because I hate typing on my phone.
Does this affect the distance of stars within a galaxy? Are all (most?) the stars that we can see with our own eyes when we look at the night sky, within our galaxy?
Seattle
Valued Senior Member
Yes, the stars that we can see with our naked eyes are in our galaxy. Expansion doesn't have much effect within our galaxy but eventually using telescopes we would be able to see fewer galaxies.
Humans will be gone by then however.
DaveC426913
Valued Senior Member
No. The stars in our galaxy - in fact, the galaxies within our local cluster - are gravitationally bound. The Cosmological Expansion is too weak to affect them.
Think of gluing a bunch of pennies to a balloon. If you inflate the balloon, you don't see the pennies getting larger. The strength of each penny is much stronger than the force of the stretching balloon.
All of them are, yes. And pretty close too.
This is a schematic of our galaxy, with its spiral arms and spurs:
We are in that little arc labeled the "local spur". It's called the Orion Arm.
Pretty much all stars we can see with the naked eye, are in that little arm.
It takes a powerful scope to make out individual stars elsewhere in the galaxy, let alone in other galaxies.
The next nearest galaxies to our own are the Magellanic Clouds and Andromeda. They are mere fuzzy blotches in our sky you could cover with your hand.
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Seattle
Valued Senior Member
Dave brings up an interesting point/fact. The furthest thing you can see with the naked eye is the blur that is the Andromeda Galaxy. You don't see individual stars (even with a telescope) but you can see the blur with the naked eye and it's about 2.5 million light years away.
The stars you see are from the closest (Proxima Centuri) about 4 light years away to stars that are a few thousand light years away. Betelgeuse (bright star in Orion constellation) is 600 light years or so from Earth, for example.
The stars you see are from the closest (Proxima Centuri) about 4 light years away to stars that are a few thousand light years away. Betelgeuse (bright star in Orion constellation) is 600 light years or so from Earth, for example.