B Is there a specific unit used to measure redshift?

[ASmartDude]

i have been learning about using redshift to measure the distance of far-flung objects, but in all my research i never saw a specific unit used to quantify how redshifted an object is. to me it seems like an oversight, because such a unit would be very useful for the study of distant galaxies, and which the impending launch of the james webb telescope and the E-ELT project underway (i think), it seems to me such a unit would be needed for these tools to be properly used. so has anybody bothered to quantify redshift, or am i the first person to think of this?

 

[Drakkith]

Redshift in cosmology is usually labeled as 'z'. It is unit-less because you divide the units out when you compare the observed wavelength to the known source wavelength. So if we observe a wavelength of 1,000 nm from a source that we know must have emitted 500 nm light, then $z=\frac{1000 nm}{500 nm}=2$.

 

[Orodruin]

Redshift is based on a ratio between wavelengths. As such it is dimensionless and does not need a unit.

Redshift in cosmology is usually labeled as 'z'. It is unit-less because you divide the units out when you compare the observed wavelength to the known source wavelength. So if we observe a wavelength of 1,000 nm from a source that we know must have emitted 500 nm light, then $z=\frac{1000 nm}{500 nm}=2$.

The definition is $1 + z = \lambda_o/\lambda_e$. For your example, the redshift would be $z = 1$ and $z = 0$ corresponds to no redshift at all.

 

[ASmartDude]

Redshift in cosmology is usually labeled as 'z'. It is unit-less because you divide the units out when you compare the observed wavelength to the known source wavelength. So if we observe a wavelength of 1,000 nm from a source that we know must have emitted 500 nm light, then $z=\frac{1000 nm}{500 nm}=2$.

that makes sense. i thought i was onto a big discovery, but i guess not. thanks for the help!

 

[kimbyd]

that makes sense. i thought i was onto a big discovery, but i guess not. thanks for the help!

The distance, by the way, is calculated based upon a model of how the universe has expanded over time. There are some online calculators that will do this, such as this one:
http://www.astro.ucla.edu/~wright/CosmoCalc.html

It's unfortunately complicated, because distances are pretty complicated in an expanding universe.

 

[Drakkith]

The definition is $1 + z = \lambda_o/\lambda_e$. For your example, the redshift would be $z = 1$ and $z = 0$ corresponds to no redshift at all.

Ah, my mistake. Thanks, Oro.