doppler red shift

[spunnery]

Could anybody who is familiiar help me with some details of doppler red shift?

In the calculation for velocity of an object(say galaxy) ,do we consider the direction of motion of body.I will explain

Object receding will form a red shift.

Object approaching will form a blue shift.

What about an object moving at an angle with the observer.Of course the value of shifting will be different.

Do we give any consideration for this while calculating velocity?

for example,

If the observer is at right angle to the direction of object,he will recieve signals without a shift????

[swansont]

If the speeds are not relativistic then there will be no shift. If v is large enough, you will see a transverse Doppler shift, from the time dilation of the moving object.

[spunnery]

If the speeds are not relativistic then there will be no shift. If v is large enough, you will see a transverse Doppler shift, from the time dilation of the moving object.

Answer not seems to be specific to my question.(may be my question is not clear).The acceleration of expansion of universe is calculated from the doppler shift of spectrum of radio waves emitted from the galaxy.Do we give any consideration (or say correction)for the direction of motion of galaxy with respect to earth(or in general say with respect to our galaxy).And if not doing so,does it make huge errors.

[swansont]

I was answering this question:

 

If the observer is at right angle to the direction of object,he will recieve signals without a shift????

 

 

The answer is no, there is such a thing as a transverse Doppler shift.

[Martin]

...The acceleration of expansion of universe is calculated from the doppler shift of spectrum of radio waves emitted from the galaxy..

 

stop you are making a big mistake.

the cosmological redshift is by definition NOT a Doppler effect and is calculated differently from the relativistic doppler formula

 

 

in your initial post you asked about the DOPPLER shift, so that has nothing to do with cosmology and the expansion of space

 

so I agree with everything swansont said. that is about doppler shift and has to do with motion in our reference frame, galaxy approaching or going away (and incidentally can also have sideways motion but this does not contribute)

 

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the cosmological redshift is a completely different ballgame

there is a lot of stuff out there which we actually observe which is receding from us at 2 or 3 times the speed of light because of the expansion of distances

 

there is no doppler formula that can translate 2c into a redshift:-)

 

you should try one of the cosmology calculators. google Ned Wright and check out his

 

if you find Wright's calculator and play aroundwith it and decide you like it, let us know and I will dig up a link to Siobhan Morgan's

 

these calculators do things like convert a redshift into a distance and a time back in the past and a recession speed. you can play around with them and see what is happening at various redshifts and get a feel for the universe.

[spunnery]

stop you are making a big mistake.

the cosmological redshift is by definition NOT a Doppler effect and is calculated differently from the relativistic doppler formula

 

 

in your initial post you asked about the DOPPLER shift, so that has nothing to do with cosmology and the expansion of space

 

so I agree with everything swansont said. that is about doppler shift and has to do with motion in our reference frame, galaxy approaching or going away (and incidentally can also have sideways motion but this does not contribute)

 

===============

the cosmological redshift is a completely different ballgame

there is a lot of stuff out there which we actually observe which is receding from us at 2 or 3 times the speed of light because of the expansion of distances

 

there is no doppler formula that can translate 2c into a redshift:-)

 

you should try one of the cosmology calculators. google Ned Wright and check out his

 

if you find Wright's calculator and play aroundwith it and decide you like it, let us know and I will dig up a link to Siobhan Morgan's

 

these calculators do things like convert a redshift into a distance and a time back in the past and a recession speed. you can play around with them and see what is happening at various redshifts and get a feel for the universe.

Thank you .(and incidentally can also have sideways motion but this does not contribute).This was the answer i was looking for.Sorry for the ignorance in the subject.

[Martin]

Thank you .(and incidentally can also have sideways motion but this does not contribute).This was the answer i was looking for..

 

have you played around with Ned Wright cosmo calculator? Anybody interested in redshift, how it relates to other cosmology quantities, is really missing a lot if they don't get some hands on with it.

 

Siobhan Morgan's is even better in the sense that it supplies the RECESSION SPEEDS that correspond to the redshift, as well as the other stuff: light traveltime and distance.

 

But with Morgan's there is a bit more bother because you have to type in 71 for the value of the Hubble, whereas Wright gives you that as a default value and there is no time wasted.

 

Check this out and do some calculating:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

 

as a landmark for you: the redshift of the CMB is z = 1100

 

but most stuff astronomers observe is z < 6

and a lot of it z <1

so Wright has a sample calculation where he puts in z = 3 as a kind of typical to show you

 

notice the number 0.73 in the lefthand margin that is the familiar "73% dark energy". he gives it to you as the default value. changing that estimate slightly would change the results of the calculation slightly

 

to use Morgan's, you have to type in that 0.73 for the dark energy and 71 for the Hubble parameter (that's the "71 km per second per Megaparse" you may have heard of) so the calculation takes a few seconds more of your time but there's the compensation that it gives you recession speeds

[grifter]

Wright's is a nice simple calculator to use; I haven't come across that before, thanks.

 

P.S. if anyone likes python (the programming language.... as oppose to the snake; )

There is a python CosmoCalculator which can be found here http://www.astro.ucla.edu/~wright/CC.python

(written by James Schombert )