- #1
hsbrown
- 3
- 0
Hello, All,
I hope I am not out of line here, this is the only cosmology forum I could find to ask a few questions...
I am considering developing a piece of software that can produce a 3D model of cataloged objects, by querying something like NED or SIMBAD, and generating this as a real time model. In other words, representing all objects where they actually are in relation to one other at a given moment, not where we are able to observe them. Maybe even try and overlay their observed positions for effect. Maybe try to play with gravity, I dunno.
However, I am having trouble locating how published distances are arrived at, and am making certain lay assumptions that may or may not be accurate. For one thing, I am assuming that the published distances of objects are calculated using the speed of light, and do not take into account the expansion of the universe...
If I input the distance of an object, and take into account the red shift that is observed, can I say with any certainty that that object's current position relative to other objects (i.e. the sun) is anything?
For example (and grins), if the (albeit short lived) published/observed distance of an object from Earth is 1 light second (300,000km), and the red shift of that object tells me that it is moving away from me at the rate of 300,000km/s then if I calculate the "actual" distance of the object for rendering purposes, would 600,000km be accurate (assuming I calculated it within a second, duh)?
Assuming that the explanation for red-shift is not EM wave propogation (and it does not play any role in the red shift) , but that it is actually a function of the objects motion, this gets confusing over greater distances when the rate of expansion of the universe is not a constant, but is either accelerating or deccelerating.
My quandary:
If one observes an object with a distance of d, and observes the red shift, applies the formula to calculate how far the object has moved away from me in the time between now and however many years, months, days, hours, seconds, etc... have passed since the light that I am observing has left the object, I would be able to calculate the actual distance of the object that I am observing, right?
Well, not really. If the object has sped up over time I have to use the red shift of progressively nearer objects (this of course assumes that the rate of expansion at any given moment in time is uniform throughout the cosmos) to calculate how much the acceleration of the object has increased over time (and the distance it is from the point of observation now), i.e if the universe is accelerating, there should be a more pronounced observable effect on red shift for nearer objects than more distant, right? The faster an object is moving away from you, the more the spectra will shift toward the red end, right?
Well, but then aren't I riding a proverbial snowball down a hill? Each progressively nearer object should have a less pronounced shift, but the shift in the spectra as I am observing it is as it was x millenia ago, and so on and so forth...
Color me confused! How can the actual real-time distance of any object be calculated when everything we can observe about it actually happened aeons ago? Including the speed at which we observe it to be moving away from us?
It doesn't really seem as though an accurate expansion rate of the universe weighted over time could be calculated or extrapolated, given that we have no way to observe how fast it is expanding right now, but only the rate as it was expanding when the nearest object to the point of observation was when the observable radiation emitted from it left the object! (say that three times fast)
Somebody must have puzzled these calculations out somewhere and have a formula for it...
Thanks
I hope I am not out of line here, this is the only cosmology forum I could find to ask a few questions...
I am considering developing a piece of software that can produce a 3D model of cataloged objects, by querying something like NED or SIMBAD, and generating this as a real time model. In other words, representing all objects where they actually are in relation to one other at a given moment, not where we are able to observe them. Maybe even try and overlay their observed positions for effect. Maybe try to play with gravity, I dunno.
However, I am having trouble locating how published distances are arrived at, and am making certain lay assumptions that may or may not be accurate. For one thing, I am assuming that the published distances of objects are calculated using the speed of light, and do not take into account the expansion of the universe...
If I input the distance of an object, and take into account the red shift that is observed, can I say with any certainty that that object's current position relative to other objects (i.e. the sun) is anything?
For example (and grins), if the (albeit short lived) published/observed distance of an object from Earth is 1 light second (300,000km), and the red shift of that object tells me that it is moving away from me at the rate of 300,000km/s then if I calculate the "actual" distance of the object for rendering purposes, would 600,000km be accurate (assuming I calculated it within a second, duh)?
Assuming that the explanation for red-shift is not EM wave propogation (and it does not play any role in the red shift) , but that it is actually a function of the objects motion, this gets confusing over greater distances when the rate of expansion of the universe is not a constant, but is either accelerating or deccelerating.
My quandary:
If one observes an object with a distance of d, and observes the red shift, applies the formula to calculate how far the object has moved away from me in the time between now and however many years, months, days, hours, seconds, etc... have passed since the light that I am observing has left the object, I would be able to calculate the actual distance of the object that I am observing, right?
Well, not really. If the object has sped up over time I have to use the red shift of progressively nearer objects (this of course assumes that the rate of expansion at any given moment in time is uniform throughout the cosmos) to calculate how much the acceleration of the object has increased over time (and the distance it is from the point of observation now), i.e if the universe is accelerating, there should be a more pronounced observable effect on red shift for nearer objects than more distant, right? The faster an object is moving away from you, the more the spectra will shift toward the red end, right?
Well, but then aren't I riding a proverbial snowball down a hill? Each progressively nearer object should have a less pronounced shift, but the shift in the spectra as I am observing it is as it was x millenia ago, and so on and so forth...
Color me confused! How can the actual real-time distance of any object be calculated when everything we can observe about it actually happened aeons ago? Including the speed at which we observe it to be moving away from us?
It doesn't really seem as though an accurate expansion rate of the universe weighted over time could be calculated or extrapolated, given that we have no way to observe how fast it is expanding right now, but only the rate as it was expanding when the nearest object to the point of observation was when the observable radiation emitted from it left the object! (say that three times fast)
Somebody must have puzzled these calculations out somewhere and have a formula for it...
Thanks