# Tag Info

### Red shifted to what?

A complementary answer to Chris's, the middle row is the spectrum at rest. A blue shift does not mean that the object ends up blue. It just means that the entire spectrum is shifted up in frequency....
• 220k

• 14k

### Conversion between extragalactic distances

You need to solve this problem $$H(a) = \frac{\dot{a}}{a} \tag{1}$$ where $a = 1 / (1 + z)$ is the scale factor, $H$ is the Hubble parameter and follows the Friedmann equation  \left(\frac{H(z)}...
• 6,514
Accepted

### What is a layman explanation for why the wavelength of light increases when space itself expands?

Here is simple explanation: Suppose a light source and a observer are in an expanding space. Now think of two subsequent crests of wave emitted by the lightsource. The second crest is emitted ...
• 8,059

### Is there cosmological redshift within the Milky Way?

Your guess is correct. The constituents of the Milky Way, and also close dwarf galaxies like the Magellanic clouds form a gravitational bound system and have therefore, seen as a single system, ...
• 1,005

### If space is "expanding" in itself - why then is there redshift?

It's pretty easy to explain if we take a classical view of an electromagnetic wave. As an EM wave from a distant star propagates towards us, the space it propagates through is expanding. Since the ...
• 7,449
Accepted

### Does redshift only affect particles of visible light?

Redshift is said to have happened when the wavelength of electromagnetic radiation increases. Blueshift, a sister phenomenon of redshift, is said to have happened when the wavelength of ...
• 6,903

### At what cosmological redshift $z$, does the recession speed equal the speed of light? How is it calculated?

The exact number depends on the cosmological model and its parameters. In special relativistic models (e.g. the Milne model), the redshift at the speed of light is of course infinite. However, in all ...
• 11.9k
Accepted

### Is the cosmic microwave background radiation red shifted?

When talking of cosmology one needs a model, and the standard model for cosmology at present is the Big Bang Model. This developed fitting observations and taking into account General Relativity ( ...
• 220k

### Red shifted to what?

The other answers (as of this posting) stick mainly to "light"... but the same concepts exist in other forms of "waves" Red/Blue Shifts and associated "Doppler effects" I want to add associated ...
• 303

### Is it possible to create a mirror that redshifts light?

As Jon Custer said in a comment, the light returning from a receding mirror will be redshifted. This is easiest to see if you consider the problem in the rest frame of the mirror. A symmetry argument ...
• 17.3k

### Is there cosmological redshift within the Milky Way?

Even if the Milky Way is expanding with the Hubble flow (and most cosmologists believe that it isn't), the expansion would be difficult to measure. The size of the Milky Way $d$ is approximately \$10^{...
• 13.4k
Accepted

### If space is "expanding" in itself - why then is there redshift?

What are the observational/experimental facts: 1)Atoms have definite spectra, with a fixed pattern, a fingerprint of the atom 2) The further away ( measured by luminocity) galaxies all around ours ...
• 220k
Accepted

### What is the cosmological redshift drift effect?

Redshift drift is the name given to the effect whereby as the universe expands, the redshift of an object will change with time. i.e. It will drift. A galaxy at a fixed co-moving distance will have a ...
• 110k