This is determined by measuring the "red shift" or "blue shift" of the star, or in other words, whether its perceived color on earth is shifted towards the red end of the spectrum or towards the blue end. This color shift effect is similar to the Doppler effect in that it is caused by the compression or rarefaction of waves by a moving object. So a star moving away from us would look slightly more red than usual because the light waves that reach us are drawn out due to the motion of the star. And conversely, a star moving towards us would look slightly more blue than usual, for the same reason.
Away, at around 18 km/s.
We can measure fairly accurately the radial speed of a star or galaxy by measuring the Doppler shift of the emitted light from the star. Stars emit specific frequencies of light, and we can measure the frequencies to determine what elements are contained within the star. But since we know exactly what the frequencies are, we can measure the precise frequencies that we measure from the star. A star moving toward us will have its light "blue-shifted", or compressed a tiny bit in frequency. The amount of the compression tells us the radial velocity. A star whose light is red-shifted is moving away from us. Radial velocity is the part of the velocity that is directly toward or away from us; Doppler shifts don't tell us anything about a star's side-to-side motion. One of the astonishing discoveries of Edwin Hubble is that most galaxies are moving away from us, and the farther away they are, the faster they seem to be receding. Some nearby galaxies are moving closer, but the more distant the galaxy, the faster it is moving moving away. He determined this by the "red shift" of the light from distant galaxies.
blue shifted
Yes. If the star is moving away from the Earth, its spectral lines will shift towards the red end of the spectrum. If it is moving towards the Earth, its spectral lines will shift towards the violet end of the spectrum. This is due to Doppler effect.
blue shifted
Away, at around 18 km/s.
they look at the sky and say hi to barney
A Doppler red-shift is a shift in recognizable features of a star's spectrum from the wavelengths where we know they belong toward longer wavelengths. Such a shift can be caused by the star's moving away from us, and that's how it's interpreted when astronomers see it. A Doppler blue-shift is a shift in recognizable features of a star's spectrum from the wavelengths where we know they belong toward shorter wavelengths. Such a shift can be caused by the star's moving toward us, and that's how it's interpreted when astronomers see it.
They can determine how fast the star is moving toward or away from us. The chemical spectral signature is used to determine the Doppler shift of the visible light reaching us. This is then used to calculate how fast we and the star in question are moving toward or away from each other.
blue shifted
blue shifted
We can measure fairly accurately the radial speed of a star or galaxy by measuring the Doppler shift of the emitted light from the star. Stars emit specific frequencies of light, and we can measure the frequencies to determine what elements are contained within the star. But since we know exactly what the frequencies are, we can measure the precise frequencies that we measure from the star. A star moving toward us will have its light "blue-shifted", or compressed a tiny bit in frequency. The amount of the compression tells us the radial velocity. A star whose light is red-shifted is moving away from us. Radial velocity is the part of the velocity that is directly toward or away from us; Doppler shifts don't tell us anything about a star's side-to-side motion. One of the astonishing discoveries of Edwin Hubble is that most galaxies are moving away from us, and the farther away they are, the faster they seem to be receding. Some nearby galaxies are moving closer, but the more distant the galaxy, the faster it is moving moving away. He determined this by the "red shift" of the light from distant galaxies.
They can be the same sort of star, it's just that the one moving quickly away from us LOOKS red BECAUSE it is moving away, while the one moving quickly toward us appears blue because it is moving toward us. This is caused by a physical phenomenon called a Doppler Shift. Edit: That's a special case, but I don't think that's what the question is about. In fact I'm not sure what the question is about exactly. It's one or those annoyingly vague questions.
Astronomers determine whether a star is moving toward or away from the Earth via the Doppler effect. Imagine a motorcycle moving past you. As it drives towards you, it has a higher frequency, and a lower frequency when it drives away. The same thing happens with light. As an object moves towards us, its light has a higher frequency and lower wavelength - this is called blueshift. As an object moves away from us, its light has a lower frequency and higher wavelength - this is called redshift.
blue shifted
Yes. If the star is moving away from the Earth, its spectral lines will shift towards the red end of the spectrum. If it is moving towards the Earth, its spectral lines will shift towards the violet end of the spectrum. This is due to Doppler effect.
I would think that current evidence suggests that the stars moving away from earth, some of them in far distant galaxies moving at unimaginably high speeds, are going much faster than stars moving toward us. The entire Andromeda galaxy is moving toward us and will collide with us in roughly 5 billion years, and it is not moving anywhere near as fast as the distant retreating galaxies.