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This is why astronomy is awesome...

frugal

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frugal

frugal

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We look up into the night sky and we generally just think of the stars and other objects as things we can see. But have you ever worked out how remarkable it is that we can see anything at all?..

Consider thw Andromeda galaxy: 2.5 million light years away. That means it is 2.4e22 meters away. Over that distance the photons emitted at a single point in time have spread out to form a shell 7.24e45 meters squared. When that light falls down the tube of you 200mm appature telescope (0.03m2 area) it means that only 1 in every 2.3e47 photons emitted actually make it to your eyepiece.

To put it in long hand for every 2,300,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons emitted from Andromeda 2.5 million years ago, only 1 makes it into your telescope. The amazing thing is that you can still see the galaxy at all.

Something to think about the next time you look up into the sky...

Sent from my GT-N7000 using Tapatalk

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Joves

Joves

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That's a fantastic post... I'm constantly amazed by how far photons have travelled to reach our eyeball, but I've never looked at it that way, as I never knew that was quite the case!

Nice to welcome a mathematician (or, at least, cleverer person than I.. which is not hard, mind you :)) to the forum!

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brantuk

brantuk

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It's amazing to think that most of the universe is empty and that the distances between stuff is so vast we find it hard to imagine such distances. Even at the speed light travels at it's a wonder we see anything at all, and that when we turn our scopes to the sky we're actually looking back in time.

It's all just so unfathomable - but interesting to see it expressed in numbers that I can't understand much past the first nine or ten zero's lol :)

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faulksy

faulksy

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We look up into the night sky and we generally just think of the stars and other objects as things we can see. But have you ever worked out how remarkable it is that we can see anything at all?..

Consider thw Andromeda galaxy: 2.5 million light years away. That means it is 2.4e22 meters away. Over that distance the photons emitted at a single point in time have spread out to form a shell 7.24e45 meters squared. When that light falls down the tube of you 200mm appature telescope (0.03m2 area) it means that only 1 in every 2.3e47 photons emitted actually make it to your eyepiece.

To put it in long hand for every 2,300,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons emitted from Andromeda 2.5 million years ago, only 1 makes it into your telescope. The amazing thing is that you can still see the galaxy at all.

Something to think about the next time you look up into the sky...

Sent from my GT-N7000 using Tapatalk

have you swollowed a maths book last night or banged your head !. nice post mate only messing

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stevetynant

stevetynant

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"To put it in long hand for every 2,300,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons emitted from Andromeda 2.5 million years ago, only 1 makes it into your telescope. The amazing thing is that you can still see the galaxy at all."

Or to put that into stupid peoples context  (ie the one I require to even attempt such contextual thinking)

The odds of winning the UK Lottery are @ 14 million to one apparantly  14,000,000   -  what a small number that now looks lol.

 

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wxsatuser

wxsatuser

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"To put it in long hand for every 2,300,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons emitted from Andromeda 2.5 million years ago, only 1 makes it into your telescope. The amazing thing is that you can still see the galaxy at all."

Or to put that into stupid peoples context  (ie the one I require to even attempt such contextual thinking)

The odds of winning the UK Lottery are @ 14 million to one apparantly  14,000,000   -  what a small number that now looks lol.

Big enough to stop me winning. :sad:

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wxsatuser

wxsatuser

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That's a fantastic post... I'm constantly amazed by how far photons have travelled to reach our eyeball, but I've never looked at it that way, as I never knew that was quite the case!

Nice to welcome a mathematician (or, at least, cleverer person than I.. which is not hard, mind you :)) to the forum!

Especially the struggle they have getting out of a star to start with......ain't nature brilliant. :cool:

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AlexB67

AlexB67

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Once you realise what we are mostly looking at in our own telescopes at home, in astronomical terms it is pretty much next door to us what we look at mostly. Now I that understand  it a bit more where these things are when I look at them every time it puts it in perspective.  I don't think I could even get a physical feel for what all the many zeros and powers mean in distance terms. I always like to think of an analogy,  or a unit system that scales more naturally. for example AU, 1 for sun earth, 9 for Saturn and so on, but even on that scale distances out into the cosmos become huge numbers, so I use something else. If galaxy a is at x, galaxy b is a x * y and so on. I can sort of picture a meter, and a field that is a 100 meters, or even a thousand if I were to look out with my eyes, but when things get into much bigger orders of magnitude it becomes difficult. 

Of course scientists do this all the time, apart from numerical issues in a computer (overflow underflow etc) It is much more natural to work in a sensibly scaled unit system and coordinates, so we set c = 1, hbar = 1/2pi  or h = 1, and not c = 2.99x10^8 m/s and 6,6 x 10^-34 Js for Plank's constant. In the molecular world we scale up the small, the elementary charge becomes 1, we don't use 1.6 - 10^-19 C.   Very hard to work and think in those terms of magnitudes.

Now as much as I am a fan of SI and metric units where possible, it is just not that practical in many cases in real world problems,  and it doesn't help to develop a good feel for things, though that is what they'll teach you in school science, not that that is a bad thing at that stage.

Sorry for the tangent and rant  :D

But now onto the more interesting stuff. Recently I came across this great little proggy, where is M13 http://www.thinkastronomy.com/M13/  A fun little bit of code to play with. It gives a brilliant presentation of the Messier objects and where things are.  Worth a download and have fun with on a cloudy night. :smiley:

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dick_dangerous

dick_dangerous

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Although I started off in Physics, I ended up studying Zoology. What I find poignant is that when we look at the Andromeda Galaxy, the light coming from it has been travelling for 2.5 million years. So when that light left that galaxy, our species didn't exist, only our Australopithecine ancestors. The light leaving now won't reach us for another 2.5 million years and I wonder if our species will exist then to see it or whether we'll have wiped ourselves out?

Maudlin thoughts for a cold, rainy November night...

DD

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Astro Imp

Astro Imp

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stupid question alert......... :lipsrsealed:

Do we know where the centre of the universe is - ie where the big bang happened, and where we sit in relation to this expanding bubble?

As I understand it there is no centre, the singularity expanded/is expanding and all of space with it.

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Kirscovitch

Kirscovitch

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Boy. You guys sure know how to make someone feel insignificant lol! 

When I see things like this it makes my brain hurt. Comprehending the Universe is almost impossible to do. I love the way we have to "dumb it down" to even begin to understand how vast everything is. One of my favorite comparisons for size is: If the earth were the size of a bb (like from a bb gun), the sun would be the size of a basketball. And if the sun were the size of a basketball, VY Canis Majoris would be a mile wide.

Or there are more stars in the Universe than all the grains of sand on all the beaches in the world,

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Paul M

Paul M

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I love space but is there a point where space ends or is it a case of  no return or does it actually do a full circle straight back to the same  point in space?

I've built a telescope that's so powerful that I can see the back of my own head. Or at least I'll be able to see it in a few billion years...

Seriously, though, I've read this conjecture a few times in relation to a closed universe. Perhaps the theory is there but I guess the geometry isn't quite so exact. Too many graviational lenses and the like?

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