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Let's begin by analogy with sound waves. You may have stood by a railroad crossing while an approaching train was sounding its horn. As the horn passes you, you'll note that the pitch of the sound (= frequency of the sound wave) changes to a lower tone. What's happening is that, as the horn approaches you, it moves a bit closer to you as it emits each peak of the sound wave's frequency, thus crowding the peaks of the waves closer together and increasing the frequency, which your ear hears as a higher pitch. As the horn moves away from you, the opposite happens -- the horn moves a bit farther away as it emits each peak of the sound wave, thus stretching out the frequency and presenting a lower pitch to your ear.

Light waves do the same thing; it's just that the speeds required to make a significant change in the frequency of the light wave (= the color of the light) are much higher than with sound. As an object emitting light approaches, the frequency of the light is higher than it would be if the object was at rest relative to you -- and the frequency of the light is lower than the rest frequency if the object is moving away.

Since blue light has a higher frequency than red light, frequency increase is referred to as "blue shift" and frequency decrease is called "red shift", regardless of the actual colors of light involved. So even radio-frequency waves can be "redshifted".

How can this be measured? It turns out that each chemical element emits its own pattern of very specific, narrowly-defined frequencies of light when heated to incandescence. We can measure those frequencies in a laboratory, and then compare them to the frequencies that we actually measure from those same chemical elements in the light coming from a galaxy (hydrogen, for example, has a strong and easily-recognized pattern of frequencies).

Knowing what the frequency was in the laboratory, and measuring the frequency as it comes from a galaxy, gives the numbers we need to plug into a formula to calculate how fast the galaxy is moving along the line of sight from us to the galaxy. If the galaxy light's frequency is higher (blue shift), the galaxy is moving toward us -- the amount of the difference between the laboratory light and the galaxy light frequency tells us exactly how fast. Similarly, redshifted light from the galaxy (by far the more usual case) tells us how fast the galaxy is moving away from us.

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What does a red shift tell astronomers about stars or galaxies?

A red shift in the light emitted by a star or galaxy indicates that it is moving away from us. By measuring the amount of red shift, astronomers can determine the speed at which the object is receding and use this information to study the expansion of the universe and the distance to the object.


Does the speed of light allow the Andromeda Galaxy to emit a blue shift?

There is some blueshift in the Andromeda galaxy as it is moving toward us. The speed of the Andromeda Galaxy relative to the sun is about 300 kilometers per second or about 0.1% the speed of light. The blueshift would be detectable by instruments but not to the human eye.


How does the speed of the star affect the spectrum?

The speed of a star affects its spectrum through the Doppler effect. If a star is moving towards or away from us, the wavelengths of the light it emits will be shifted towards the blue (blue shift) or red (red shift) end of the spectrum, respectively. This shift can provide information about the star's velocity and direction of motion.


What does the red shift of the galaxies tell us about their motion with respect to the Earth?

Less than you'd think. At extreme distances, the red-shift is caused by metric expansion more than by motion. So to be able to gauge the speed of an object relative to you, you'd first have to determine the pseudo-speed caused by metric expansion.


How can an object's red shift tell us how fast the object is moving away from earth?

The amount of reddening is directly proportional to the speed of the object away from the observer (if the object is moving tangentially, even at a high speed, no red shift will be noticeable. Follow the link below for a bit more information on the mathematics and measurements of red shifts.

Related Questions

What does a red shift tell astronomers about stars or galaxies?

A red shift in the light emitted by a star or galaxy indicates that it is moving away from us. By measuring the amount of red shift, astronomers can determine the speed at which the object is receding and use this information to study the expansion of the universe and the distance to the object.


Does the speed of light allow the Andromeda Galaxy to emit a blue shift?

There is some blueshift in the Andromeda galaxy as it is moving toward us. The speed of the Andromeda Galaxy relative to the sun is about 300 kilometers per second or about 0.1% the speed of light. The blueshift would be detectable by instruments but not to the human eye.


How does the speed of the star affect the spectrum?

The speed of a star affects its spectrum through the Doppler effect. If a star is moving towards or away from us, the wavelengths of the light it emits will be shifted towards the blue (blue shift) or red (red shift) end of the spectrum, respectively. This shift can provide information about the star's velocity and direction of motion.


How do you know your Galaxy rotates?

Astronomers can determine the rotation of a galaxy by measuring the Doppler shift of the light emitted by stars and gas within the galaxy. The rotation speed can be calculated by observing the difference in wavelengths of light from objects moving towards or away from us. This information allows scientists to create maps of how the galaxy's stars and gas are moving.


Does need for speed shift have ferraris?

Need for speed does not have shift have Ferraris


What is the speed of bikes on Google Maps?

Google Maps does not provide real-time information on the speed of bikes.


Is there free drive in Need for Speed Shift?

There is no free drive in Need for Speed Shift.


Where Can You Find Need For Speed Shift?

You can get need for speed shift at walmart & game stop.


Is it true or false when returning radar energy can show direction and speen of raindrops?

True. When radar energy is returned, it can provide information on the direction and speed of raindrops. By analyzing the Doppler shift of the returned signal, meteorologists can determine the speed at which raindrops are moving towards or away from the radar site.


Which is the best android game need for speed shift or need for speed hot pursuit?

The best Android game between Need for Speed Shift(ShiftNFS) and Need for Speed Hot Pursuit is Need for Speed Shift.


1999 5 speed beetle won't shift gears?

Not enough information. Will the car shift gears with the engine off? Is the gear shifter stuck in one particular gear?


Will the speed sensor in a Chevy s10 blazer make the truck not shift?

That is True.. A faulty speed sensor will cause no shift or late shift..