Astronomy Stack Exchange
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Questions tagged [redshift]

Questions related to the phenomenon whereby electromagnetic radiation (such as visible light) generated by an object moving away from an observer will have increase in wavelength (i.e. shifted toward the red end of the spectrum) once it reaches the observer.

According to the Wikipedia entry on redshift.

In physics, redshift happens when light or other electromagnetic radiation from an object moving away from the observer is increased in wavelength, or shifted to the red end of the spectrum. In general, whether or not the radiation is within the visible spectrum, "redder" means an increase in wavelength – equivalent to a lower frequency and a lower photon energy, in accordance with, respectively, the wave and quantum theories of light.

Redshift also occurs when light leaves a gravitational potential (gravitational redshift) or due to the expansion of the universe (cosmological redshift). In the latter case, it indicates the change in the scale factor between the lights emission and observation.

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The "k-effect"?

I'm reading some older materials which refer to something called the "k-effect". This was described as "hot stars in the Sun’s neighborhood are moving away from us in all directions, while cooler stars do not". I tried looking in Google, but the…
Maury Markowitz
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Why is the letter *z* customarily used to denote redshift?

What events led to the nearly universal acceptance of the letter "z" as the denotation of redshift? What did the letter originally stand for?
George A. Solodun
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How is z calculated in red shift observations?

If z is calculated using the ratio between observable wavelength and emitted wavelength, how do we know the emitted wavelength of a star that is moving away from us? Wouldn’t we have to be at a constant distance from the star to know that value?
tomh
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Can space-time expansion destroy light?

I know that light shifts from high frequency(like gama rays) to low frequency (like radio waves) when traveling throw a gravitational field, this is called red shifting. My question is: Is there a limit to this, what happens to the light wave when…
user7996469
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"True" motionlessness - red shifts and CMB

This is a question I asked years ago in an astronomy course, but to which I never got a straight answer. Please feel free to correct me if any of my assumptions here stray from facts. It goes like this: To any observer, at large enough scale the…
JNW
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Why is there no time in the distance equation using Hubble constant, red shift and speed of light?

So I had some problem and I think I solved it, then I began to dig out things around it and I found some equations using red shift etc. to get speed of the object in Universe relative to us and then I found this one: distance=speed of light/Hubble…
Vojta Klimes
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How Do we know about redshift?

Okay so scientists use the red shift to know that galaxies are moving away from us faster than light. How do we know that its not just red light from red stars. i mean most stars are in the infrared spectrum.
House
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Why does a Decision Tree produce lines in photometric redshift predictions?

In this paper, the authors compare the speed and accuracy of various machine learning algorithms to produce photometric redshift estimates: Why does the DT regressor put the estimates into bands along the True z axis? The only thing I can find in…
Jim421616
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Redshift Formulas

I was wondering where does the formula for redshift $$z=\frac vc$$ come from? Can it be derived from the definition of redshift $$z={\lambda_{observed} - \lambda_{emitted}\over \lambda_{emitted}}?$$
space nerd
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Is Blue Shift just as provable as Red Shift?

I've heard a lot about red shift and it sounds pretty legit. But it made it sound as if blue shift was a lot less likely. Can anyone help me out?
David Johnson
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Redshift observation at different wave length

Can one star be observed at different wave length show different redshift ?
Edy A.
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Are all planets/galaxies moving away from *us*?

From what I can see in a physics textbook page (on redshift), it seems to imply that all planets/galaxies emit red, rather than blue waves (for red-shift). Wouldn't this mean that everything is moving away from us and that we're the centre of the…
user15682
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Are there viable explanations for the red shift of distant galaxies other than the accelerated expansion of the universe?

I was told that photons lose energy (= increase their wave length) when moving away from mass and gain energy moving towards mass. Could this increased red shift of photons, originated a long time ago, come from the fact that they started in an old,…
Cosinus
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Does red shift need to compensate for space expansion

Distant galaxies are moving as space expands, not moving through space. So a photon coming to us from them has to come back through distorted space. So is not spacetime distorted, so the photon has to go through an area where time slows down. So…
Roy Proudman
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