How do we accurately measure the distance to other galaxies?

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Offline thedoc

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Konrad Higgins asked the Naked Scientists:

I have a question about measuring the distances and recession speeds of galaxies, which is also linked to dark matter/energy.

My understanding is that measurements indicate that space is expanding, and it is this that is responsible for the redshift observed by inter alia Hubble.

My question is, are all galaxies moving away from each other only because of the expansion of space, or if one was to remove this expansion effect could they be moving towards each other and or away from each other? It is perhaps difficult to word - I am imagining a rubber band with two points representing two galaxies of static distance controlling for the expansion of space. Stretch the rubber band and the distance increases between the points. If you replace the points with two ants, and stretch the band, the distance between them may increase although the ants themselves may be walking towards each other or it may increase faster than anticipated if they are walking away from each other. Is the universe like the points or the ants?

It occurs to me that if, controlling for the expansion of space, the galaxies are moving together in some regions of space, or away from each other in others, this could indicate the influence of dark matter or energy, or some other interesting effect.

I imagine there is a problem - measuring the actual distances to the galaxies to then control for the expansion of space. I understand that standard candles were used to measure distances to galaxies and from this the distance/red shift relationship observed. Do we have reliable candles for a good proportion of galaxies I wonder, or when we hear of galaxies being at such and such a distance, are we more typically measuring the red shift from them and using that to obtain the distance. If the latter then presumably one would not be able to tell if, controlling for the expansion of space, they are going away from or towards us. Or are there other ways of measuring distance?

Keep up the good work!


What do you think?
« Last Edit: 20/04/2014 04:06:17 by evan_au »


Offline yor_on

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It's a nice idea, and should be noticeable I think, presuming that a accelerating expansion is the same everywhere in a universe, a 'constant' of sorts even when accelerating.

You can see something called the Hubble constant there.
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Offline evan_au

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There is a random motion superimposed on the general expansion of the universe.
So the Andromeda galaxy in our local cluster is moving towards our Milky Way galaxy, and is expected to eventually collide.

A hierarchy of "standard candles" are used for successively longer distances, including parallax of nearby stars, brightness of variable stars, peak brightness of supernovae and galactic redshift.

For extreme distances, redshift is the best available measure.


Philosophy Thought

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« Reply #3 on: 26/06/2014 06:37:26 »

Hello, professors and students of the University of Cambridge, I liked to comment, saying ... Why Do not look in the holy quran for Muslims?There are facts you are absent for them in all the sciences

I watched a program to channel scientific translated to Arabic speaking about the science of the universe and space, I wanted to add some words, but I could not so I went to a Web site for one of the universities in the world to say there are things to talk about in the universe ..

You can not hide the fact ... that the Arabs who found science, then the West has created a technical

Read about the ancient Muslim scholars who spoke in science
Described the universe, space and without a spacecraft..

I'm sorry for incorrect writing ... I'm not good speak english


Floyd Baker

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« Reply #4 on: 09/04/2015 14:32:01 »
Since no one seems to understand what light is, red shift showing the cosmos expanding is most certainly an  illusion.     My understanding of light, as even Einstein thought possible, is that photons have some, immeasurable to us, mass...   As shown by gravitational lensing, etc..  And so can be slowed by gravity more and more as they travel further and further.

The slowing would not be noticeable because it only amounts to a few nm on the electromagnetic spectrum which is now being attributed to the galaxies moving away...

So a true physics description of light is that photons are particles with mass traveling at 'c', radiating a frequency that also travels outward at 'c'.     With both moving at 'c' in the one direction, the wave in that direction is blue shifted to the max, with all points of the wave front being in the same place at the same time.   So the frequency simply cancels itself out in that direction...  

But looking away from the center line of travel, one sees the wave front being blue shifted less and less.  And as it travels outward away from the particle proton to hit the flat plane traveling just ahead of it.., the waves become longer and longer.   This then is the *entire* cosmic electromagnetic spectrum radiating outward in all directions from the center line of travel.  The visible spectrum will look like the colored circles of a target.  

The slowing of the particle photon will not decrease the speed of the outward going wave front, but it will bring the entire EMS that the particle produces closer to the center line of travel..   This will happen in infinitesimal increments the further it travels through the cosmos.  Thus giving the illusion of all galaxies out from earth being red shifted more and more as their distance from earth increases.

This is major information...  Believe it.  

There is much more at