Celestial Sphere
24 Apr 2013 6:35:50 UTC
Topic 196921
(moderation:
Since I'm nearly due to release a screensaver/simulator which tries to illustrate what could be called 'positional astronomy', I thought I'd fire up an explanatory thread to describe some concepts therein. This of course will be a 'ready reckoner' or approximate narrative to hopefully give a basic grounding. As usual there will be many 'truths' which on closer inspection turn out to be first attempts that subsequently can/will be refined when you zoom into detail. I'll try not to bite too hard into any ( Special or General ) Relativity Cookies. So let's not be too pedantic .... and please interrupt with any questions! :-)
What I mean by 'positional astronomy' is an approach to describe where things are out there.
One obvious constraint is that we have yet to develop the ability to significantly alter our viewpoint within the cosmos. So we can't, outside of TV shows, sneak off to even the next star system. The farthest any man-made probe has been has barely broached the massive distance to the Alpha Centauri system. This is another sense of the word 'astronomical' which primarily means 'of the stars', but when applied to distance or numbers as 'astronomical' then it means huge compared to any human or everyday scale. The Hitch Hiker's Guide to the Galaxy gives a good working definition, yet to be beaten I feel :
Quote:
Space is big. 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.
Thus when someone states that the distance to Alpha Centauri is such-and-such, it is definitely NOT because anyone has gone out and back with some suitably long piece of string with marks on it. So it isn't a case of counting the number of repeated ( standard ) distance units up until some total that we then denote as 'the distance to X is ...'. That's typically what you would do here on Earth, say in the back yard outlining a plot to place a garden bed for instance. Ultimately astronomy does come down to quoting lengths in terms of the metre or something else on human scale. But what we wind up doing is creating a set of distinct but related proxy measures that can be calibrated one against the other. Such work is by no means done and dusted, as studying and determining the scale of various components in the cosmos is very much an active area of concern and crucially so. Which brings up the next general issue ....
We haven't been around for very long in terms of cosmic time. Thus for the Hitch Hiker's quote above you could insert time concepts instead of distance and get the same type of truth. Thus if you pick any human time scale what-so-ever - up to and including our emergence as a species since little mammals were running around under the feet of dinosaurs - then that's brief compared with the time scales of astronomical interest. Again, no one has been sitting around with some clock marked with a human scale of hours, say, and toting them up to claim 'the age of X is ...'. Naturally there are no time machines yet available either, so any movement in time ( well, other than 'forwards' at the usual rate ) is just as unachievable for us as significant movement in space away from Earth.
So now you'll note that I'm linking a discussion about positions in space with a consideration of time as well. That turns out to be inevitable, as we will see, but before getting to that we have to sort out a rather deeper question first ....
In what sense is 'astronomy' a science?
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Celestial Sphere
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I have a question...WHY haven't we sent a fast moving probe to someplace like Alpha Centauri? I KNOW it will take a VERY long time, but the US military has some extremely fast burning missiles that can accelerate to many times the speed of sound while near the ground, sending them on a fast burning path to A.C. seems like a no brainer. Yes I understand that they can't possible carry enough fuel to burn fuel all the way there, but they should be able to be launched by an airplane and then fast burn enough fuel to get them to astronomically high speeds in the vacuum of space with its near zero resistance. Is the problem 'the things in the way' that it would be impossible to avoid, as in way to fast to maneuver? I am thinking near half light speed or so. If this is OT just mod it.
RE: I have a question...WHY
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Well, there's a few issues there but essentially the problem has an exponential character. If I lift fuel from the Earth's surface to a certain distance away then I have to contribute energy to lift it to such a point. That's gravity. Even if well away from Earth - 'free space' - then if the probe is at some given speed, for it to then accelerate onwards from that speed it has to use fuel which has already been brought up to that speed. If you invoke special relativity it only makes it worse as a given chunk of material is more resistant to acceleration at higher speed than lower, what is deemed as an increase in inertial mass. For instance most of the fuel in the tanks at the launch tower ( eg. Apollo ) is there to lift other fuel to be used later, not so much the payload of interest in a direct sense. It's mass with inertia either way whether called fuel or payload. Bringing it more gradually to height - aeroplanes or whatever - doesn't escape that penalty. So a one-shot effort won't work. You'd have to accumulate a cache of fuel well away from Earth - by spending fuel to lift other fuel - and then set off to A.C. It would be an enormous mountain.
What underlies this is the available energy density of the fuel. Chemical burning only ever involves re-arranging electrons to release ( electromagnetic ) energy to be available to push things around eg. the hot gas in the rocket combustion chamber kicks the craft forwards while itself shooting out backwards. So only a small change in the energy of the combustible materials ( compared to it's mass/energy equivalent via E = m * c^2 ) is doing the propelling. What you really want is to tap into either the weak and/or strong nuclear forces. Antimatter say. That's where a serious interstellar boost could come from. You don't lose the exponential behaviour above but you get payback in spades to tame it. :-) :-)
Cheers, Mike.
( edit ) I ought clarify : by 'exponential' one means that producing a change in something depends upon how much something is already there. This is formalised mathematically as the first derivative of some quantity being proportional to the quantity itself. When analysed in detail then 'fuel lifting other fuel' has that nature.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
RE: RE: I have a
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I sort of understand, but was thinking the aeroplane would be doing all the initial heavy lifting then the 'craft' would have enough to move on into space from there, similar to the old X-15 test flights or the newer Space-X test flights. Use off board fuel to get it off the ground and then use onboard the 'craft' fuel to move it from there on. Yes I understand the huge Saturn V type rockets were needed to lift the fuel and not the people in it, but what if you started at 90k feet? Wouldn't that mean less gravity and therefore less fuel needed to overcome it, so the same fuel would get you further faster. Yes I know that trying to lift the Saturn V to 90k feet by an external vehicle is just impossible, but I wasn't thinking of THAT much fuel. I think there is a formula about gravity and distance and how the further from an object you are the less energy is needed to break its grasp. And yes I know that gravity knows no bounds, but the further away you are from a specific object the less it affects you. The Earths gravity affects the Moon, and vice versa, but the Moon is slowly pulling away and will eventually be lost to us and go elsewhere.
And yes I have thought of the possibility of a 'gas station' in orbit, but the possibilities of a failure and reentry are probably too great to make it a reality in the near future. But it would make planetary flight easier and faster if you only had to carry enough fuel to get to the orbiting 'gas station' and then fill up and move forward from there. Similar to how the SR-71 flew, it leaked so bad on the ground it could not carry enough fuel for its missions, so the first thing it did after take off was stop and refuel.
And until we figure out how to safely use other types of fuel we are sorta stuck with chemical based stuff. Yes I know we have other kinds as prototypes, a couple actually in flight right now, but they are not proven to work over the long run yet. I have always thought it would be some kind of gravitational thing or other, but have NO CLUE how! A person can jump with all their might, anything can, but they will ALWAYS be pulled back down by the Earths gravity! BUT pick up a small refrigerator magnet and then pick up a paper clip with it, and that paper clip will NEVER fall back to Earth! Never as in our life time, not as in Universe time, as I know individual magnets lose their force over eons of time.
I don´t wanna interfere to
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I don´t wanna interfere to much in your discussion but there exists a company which plans are to earn materials from asteroids and the space included Gas.
I´ve read that they wann start with that(if all runs well as planned)in 2020
Here´s a short video of them.
http://deepspaceindustries.com/media/videos/
That could be the beginning of starting a Plane, Rocket or Spaceship that doesn´t need to fight against the gravity on earth at launch and you don´t need extra fuel.
And here you can find
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And here you can find visualization for space exploration.
http://spacehabs.com/
I think that pictures are great.
These are all great ideas,
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These are all great ideas, and it's not that such things can't be done ( as in they breach some well known physical laws ) but is there the collective will to do it? It has to be a collective effort and as per Deep Space Industries a ( very ) long game indeed. Most people realistically will never meet their great grandchildren, and would be insufficiently able to discard shorter term concerns if there was a trade-off, for that is the time scale of substantial return. One can be incremental of course - again as per DSI - but there still requires a trans-generational persistence of intent. Such intent has to remain specific and not diluted, thus certainly not the province of those with short personal horizons in time and space. That is hard for beings whose dominant neurological characteristics deal with immediacy. So if space is 'big' and 'old' and in want of discovery and conquest, can our tiny minds cut it??
[ Well, that's the view from an older guy who has seen more instant idiocy than I care to recall .... so maybe I'm the wrong one to be asked! :-) :-) ]
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Sorry that my english isn´t
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Sorry that my english isn´t good enough to understand you very well,and the translater doesn´t build sentences very good. :)
What i wanted to say and show is that there are many things in progress.
For spaceships or stations there are plans to build them with 3d print(i forgot to say)but the big problem which exists i think is to solve the problem with the artificial gravity.
Weightlessness is not a good thing for a human to be exposed to for longer time.
It makes us ill and desoriented and we need our feet on the ground.
If someone could give us a Stargate to travel between exoplanets which have the gravity of our earth, we wouldn´t need an artificial gravity necessarily.
But perhaps the gravitational wave serch makes that possible in a few hundred years or so.
Hopefully nobody is feeling attacked, it´s just a little joke.
I have to correct me(i wrote
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I have to correct me(i wrote early in the morning)
it´s not a joke i think really that it will be possible to travel from 1 planet to 1 another(for example) in the future "instantaneously" but this has nothing to do with a real time machine how some people think.
I think a time machine(for travelling back in time as it´s shown in movies) would be very difficult to impossible.
All Vehicles we know bring us faster to our destination.
So travelling if instantaneously or not is more imaginable then travelling back in time.
RE: I have to correct me(i
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IF the the 'new' theories of the Universe being like a big ball and if we could see far enough 'back' or 'around' we would see ourselves, then yes it could be possible to go 'back' in time. However that is all HIGHLY theoretical and not proved. Some people say that we are less then 400 thousand years from 'seeing' the big bang happen, I don't know if it's true, but it is interesting to me.
RE: Some people say that we
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I think that refers to the cosmic microwave background which is an imprint of the radiation produced with the Big Bang but representing a time some ~300K years after that. Around that time most photons generally 'decoupled' or largely ceased interacting with matter as the temperature had subsided to the point where electrons and protons could form low mass atoms like hydrogen and helium ie. not ionised. That 'gas' of non-interacting photons has likewise 'cooled' with the further expansion of the universe since and in fact is one of the main points of evidence that there was such a thing as a Big Bang at all.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal