How do scientist measure the speed of a galaxy?

Answer 1

To measure a galaxy’s speed, astronomers spread out its light into a spectrum (rainbow). This reveals the range of wavelengths-from (blue) to (red)-emitted by its stars. The spectrum is crossed by dark absorption lines, which correspond to the absorption of light at particular wavelengths by chemical elements in the stars’ atmosphere.
If the galaxy is moving, the position of these lines changes. A galaxy approaching us appears to have its wave fronts , and so its lines shift towards the blue, short-wavelength end of the spectrum. Most galaxies are moving away, and so their trailing wave fronts shift the lines to the red. The degree of this shift gives the galaxy’s speed.

Answer 2

If you mean how fast is it moving relative to us, then the answers that talked about doppler shifts were correct. If you want to know the speed of rotation you have to measure the doppler shift at different positions across the galaxy - one side should have a greater red shift than the other because those stars are moving away from us at a higher speed.

Answer 3

By spectroscopy. They measure the red/ blue shift of a galaxies light wavelengths to determine how fast it is moving away or towards us.

Answer 4

the amount of redshift. as a galaxy is moving away, the light wavelength is spread out by the spreading of space-time, making the light redder. by determining how much redder it is, and how far away it is, they can then calculate how fast it's moving

Answer 5

With a big tape measure and a watch (timex)

Answer 6

In light years.

Answer 7

With a radar gun...but just a little bigger than what the cops have.