Star movement

[sigma]

When you get a red or blue shift on stars, are they moving in the same direction at different speeds or are they moving either way from or towards each other.

[rojash]

Red shift, they are moving away from you so that the wavelength of the light reaching you appears stretched.

Blue shift, the wave length appears shortened because they are moving towards you.

The shift indicates the direction of their movement relative to you.

If ALL of them appear shifted in the same direction (e.g. all red-shifted, and thus all moving away from you) this would appear to indicate that the universe is expanding, and hence that they are all also moving away from each other.

[Loosehead]

In reality individual stars will give neither as they are in our own galaxy and hence are not moving very much relative to each other and our own star. I am assuming you are referring to galaxies and red shifted ones are moving away and blue shifted ones are moving toward. The red/blue shift applies to us the viewer not to the objects themselves and their relation to each other.

[Clanad]

Additionally. stars in any spiral galaxy measureable for shift to determine speed and direction relative to us, will red shift in the areas of star movement away from us while the advancing spiral arms (relative to us) will blue shift. Hence a galaxy that has spiral arm construction (similar to our Milky Way) will display both red and blue shift in individual stars...

[mibn2cweus]

Red/blue shift is the visual equivalent of the Doppler effect on a sound source moving toward or away from the listener, as observed by the changing pitch of a siren on a passing emergency vehicle for example.

[rojash]

In fact red/blue shift IS the doppler effect and the term was not applied to sound waves until 3 years after Doppler described the effect regarding light.