# How do you calculate the radial velocity of a galaxy?

##### 1 Answer

Write your answer here...

Start with a one sentence answer

Then teach the underlying concepts

Don't copy without citing sources

preview

?

#### Answer

Write a one sentence answer...

#### Answer:

#### Explanation

Explain in detail...

#### Explanation:

I want someone to double check my answer

Peter
Share

Mar 8, 2017

#### Answer:

Rotational speed is directly correlated to a galaxy's luminosity.

#### Explanation:

Rotation speed is a measure of a spiral galaxy's total mass. This is known as the "Tully-Fisher relation." Radiation from the galaxy where matter is generally approaching us is blueshifted by the Doppler effect. Radiation on the other side is redshifted by a similar amount. The overall effect is that line radiation from the galaxy is "smeared out" or broadened, by a galaxy's rotation. The faster the rotation the greater the amount of broadening.

Was this helpful? Let the contributor know!

Describe your changes (optional) 200