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Just to add a simple question but maybee I'am to simple to answer it on my own in calculations about the size of the observable universe and hubble spheres and all of that how do you determine the location of an observed galaxy, from its redshift you can get a relative velocity between us and them but surely u need to calibrate these calculations with an object you know is at particular fixed distance from us and quite frankly to put me out of this misery which object is it.

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  • $\begingroup$ Have a look at en.wikipedia.org/wiki/Cosmic_distance_ladder $\endgroup$ – Photon Feb 7 '17 at 22:50
  • $\begingroup$ Yeah Thanks Photon this has helped clear some things up parallax mentioned in the article had occurred to me too but luminosity like i've mentioned below how can it account for the fact that a brighter object may have similar luminosity to closer object we observe here on earth surely you cannot calculate an accurate distance because it may just be brighter than the closer one. $\endgroup$ – 8Mad0Manc8 Feb 9 '17 at 17:16
  • $\begingroup$ I'm not sure if I understand you correctly, but for such measurements special objects with almost fixed luminosity are used, like supernovae of type Ia which have a very low variance in luminosity. $\endgroup$ – Photon Feb 10 '17 at 17:54
  • $\begingroup$ That's interesting I can understand now how you can use the information to calculate distances, I wouldn't have imagined the variance in luminosity to be very low I would have thought such an objects luminosity to be greatly determined by its age, and indeed every other object in the night sky. $\endgroup$ – 8Mad0Manc8 Feb 12 '17 at 20:17
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Redshift is not the only measurement or method of judging, and thus it can be calibrated by measuring with another system. This is akin to calibrating a visual rangefinder which uses parallax by using a laser rangefinder.

If memory serves they used Cepheid variables (variations in luminosity and pulsing light) in Cepheus stars, whose properties are constant and known.

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  • $\begingroup$ Acquiring its cartessian coordinates relative to us quite frankly relative to any celestial being has to be an approximate using luminosity be cause you have no referrence point sureley the only observable point in the universe we have reference to is the moon after all we have been there and have been able to calculate the distance thankyou Tom for your efforts and all the other actors who took part. my question remains the universe is expanding and objects further away from us a moving at a greater velocity but there proper distance can only be speculated surely. $\endgroup$ – 8Mad0Manc8 Feb 7 '17 at 23:05
  • $\begingroup$ windows2universe.org/kids_space/cepheid_variable.html It is very wrong to conclude that the Moon is the only reference point. We know, for example, that the speed of light is a constant. $\endgroup$ – Jake Watrous Feb 7 '17 at 23:14
  • $\begingroup$ We know that the speed of light is a constant with reference to every other point in the universe but its constance does not help us in calculating the distance a galaxy or point is away from us it only enables us to calculate its redshift and its relative velocity to us if we had the moons redshift to us we could calculate any object relative to the earth because we have an identifiable reference point not these general estimations the scientific public community give us you need a static reference point to the earth yes the universe expands at a greater speed the further you r away from it $\endgroup$ – 8Mad0Manc8 Feb 7 '17 at 23:29
  • $\begingroup$ Using an objects luminosity surely that has problems how can you tell a distant object is not further away than another similar luminous object it may be simply brighter than it and this accounts from the similar luminosity observed here on earth. Surely then they must use both concepts of redshift and luminosity in conjuction to enable us to calculate on objects distance from us. $\endgroup$ – 8Mad0Manc8 Feb 9 '17 at 16:48

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