Electro-Magnetic
Electro-Magnetic Radiation
Part: 4 of 4
The Doppler Effect
Imagine that
Imagine that while on his route,…
…that a mailman passes
…that a mailman passes a stationary ambulance.
mailman
…that a mailman passes a stationary ambulance. mailman
…that a mailman passes a stationary ambulance. mailman
stationary ambulance …that a mailman passes a stationary ambulance. mailman
…that a mailman passes a stationary ambulance. stationary ambulance
At that exact moment,
At that exact moment, the driver receives a call,…
…and begins to blast
…and begins to blast the ambulance’s siren.
Sound waves begin to disperse
Sound waves begin to disperse in all directions,…
…both behind the ambulance,
…both behind the ambulance, and in front of it.
behind …both behind the ambulance, and in front of it.
behind …both behind the ambulance, and in front of it.
behind …both behind the ambulance, and in front of it.
behindin front
Since the ambulance
Since the ambulance is stationary,…
…then the sound waves leave the ambulance
…then the sound waves leave the ambulance with equal spacing.
equal …then the sound waves leave the ambulance with equal spacing.
The pitch is determined
The pitch is determined by the wavelength,…
…and this pitch
…and this pitch has a medium tone.
(medium tone)
The sound waves
The sound waves pass the mailman.
The mailman knows
The mailman knows there is an emergency,…
…so he decides
…so he decides to get out of the way.
As the ambulance
As the ambulance begins to move forward,…
…its sound waves also
…its sound waves also begin to change their spacing.
From this…
equal spacing From this…
…to this.
unequal spacing …to this.
The waves in front
The waves in front of the ambulance…
…are now a lot
…are now a lot closer together.
closer together …are now a lot closer together.
And the waves
And the waves behind the ambulance…
…are now a lot
…are now a lot farther apart.
farther apart …are now a lot farther apart.
Since tone is determined
Since tone is determined by the wavelengths,…
…then the wavelengths on front side
…then the wavelengths on front side will now sound higher in pitch,…
higher in pitch …then the wavelengths on front side will now sound higher in pitch,…
…while the wavelengths on the back side
…while the wavelengths on the back side will now sound lower in pitch.
lower in pitch …while the wavelengths on the back side will now sound lower in pitch.
This concept is called
This concept is called the “Doppler Effect”.
The Doppler Effect is defined
The Doppler Effect is defined as the change in the wavelengths…
…due to the relative motion
…due to the relative motion between the observer and the source.
The key term here
The key term here is “relative motion”,…
…because it doesn’t matter which object
…because it doesn’t matter which object is doing the moving.
So whether the ambulance
So whether the ambulance is stationary…
(stationary)
…and the mailman (stationary)
…and the mailman runs towards the ambulance,… (stationary)
…and the mailman runs towards the ambulance,… (stationary)
…and the mailman runs towards the ambulance,… (stationary)
…and the mailman runs towards the ambulance,… (stationary) (forward motion)
…or whether the mailman
is stationary…
…or whether the mailman is stationary…
…or whether the mailman is stationary…
…or whether the mailman is stationary… (stationary)
…and the ambulance (stationary)
…and the ambulance moves towards the mailman,… (stationary)
…and the ambulance moves towards the mailman,… (stationary)
…and the ambulance moves towards the mailman,… (stationary)
…and the ambulance moves towards the mailman,… (stationary) (forward motion)
(stationary) (forward motion)
…is irrelevant. (stationary) (forward motion)
Because either way,
Because either way, relative to each other,…
…there is motion which exists
…there is motion which exists between the (2) objects.
And it’s this relative motion
And it’s this relative motion between the (2) objects…
…which causes the Doppler Effect
…which causes the Doppler Effect to be created and detected.
The shortening of the wavelengths
The shortening of the wavelengths on the front end of the ambulance…
…is called
…is called a “blue shift”.
blue shift …is called a “blue shift”.
And the lengthening of the wavelengths
And the lengthening of the wavelengths on the back end of the ambulance…
…is called
…is called a “red shift”.
red shift
Since the blue wavelengths
Since the blue wavelengths of visible light are shorter,…
shorter Since the blue wavelengths of visible light are shorter,…
shorter
…and since the red wavelengths
shorter …and since the red wavelengths of visible light are longer,…
shorter …and since the red wavelengths of visible light are longer,…
shorterlonger …and since the red wavelengths of visible light are longer,…
shorterlonger
shorterlonger …then we use words
shorterlonger …then we use words like “blue” and “red”…
shorterlonger
shorterlonger …to denote the changes in wavelengths
shorterlonger …to denote the changes in wavelengths for all types of waves.
shorterlonger
shorterlonger And even though these waves
shorterlonger And even though these waves are sound waves,…
shorterlonger
shorterlonger …the Doppler Effect will also work
shorterlonger …the Doppler Effect will also work for all other types of waves as well.
So as the ambulance
So as the ambulance begins to race forward,…
(forward) So as the ambulance begins to race forward,…
(forward)
…its sound waves start heading (forward)
…its sound waves start heading for the mailman. (forward)
…its sound waves start heading for the mailman. (forward)
…its sound waves start heading for the mailman. (forward)
…its sound waves start heading for the mailman. (forward)
…its sound waves start heading for the mailman. (forward)
…its sound waves start heading for the mailman. (forward)
…its sound waves start heading for the mailman. (forward)
…its sound waves start heading for the mailman. (forward)
As they pass the mailman,
As they pass the mailman, he hears a higher pitch,…
higher pitch As they pass the mailman, he hears a higher pitch,…
higher pitch As they pass the mailman, he hears a higher pitch,…
higher pitch As they pass the mailman, he hears a higher pitch,…
higher pitch As they pass the mailman, he hears a higher pitch,…
…and he knows for certain
…and he knows for certain that the ambulance is approaching.
So as he goes
So as he goes to take a look,…
…he realizes that today
…he realizes that today just wasn’t his day.
Houston, …he realizes that today just wasn’t his day.
Houston, we have a problem! …he realizes that today just wasn’t his day.
The Doppler Effect
The Doppler Effect and Stars in Motion
Imagine that a star
Imagine that a star were (5) LY away from the Earth.
5 LY Imagine that a star were (5) LY away from the Earth.
How could we know
How could we know whether or not…
…that the star were moving either towards
…that the star were moving either towards or away from the Earth?
The Doppler Effect
The Doppler Effect can be useful…
…in determining the motions
…in determining the motions of any moving star.
shorterlonger
shorterlonger Imagine that the star
shorterlonger Imagine that the star were not moving…
shorterlonger
shorterlonger …and reveals the absorption line pattern
shorterlonger …and reveals the absorption line pattern shown above.
shorterlonger …and reveals the absorption line pattern shown above.
shorterlonger
shorterlonger But if the star begins to move slowly towards the Earth…
shorterlonger But if the star begins to move slowly towards the Earth…
shorterlonger But if the star begins to move slowly towards the Earth…
shorterlonger But if the star begins to move slowly towards the Earth…
slowly shorterlonger But if the star begins to move slowly towards the Earth…
slowly shorterlonger
slowly shorterlonger …then its absorption line pattern
slowly shorterlonger …then its absorption line pattern will be Doppler shifted…
slowly shorterlonger
slowly shorterlonger …towards the blue end
slowly shorterlonger …towards the blue end of the spectrum.
slowly shorterlonger …towards the blue end of the spectrum.
slowly shorterlonger …towards the blue end of the spectrum.
shorterlonger
shorterlonger And if the star begins to move
shorterlonger And if the star begins to move even faster towards the Earth…
shorterlonger And if the star begins to move even faster towards the Earth…
shorterlonger And if the star begins to move even faster towards the Earth…
faster shorterlonger And if the star begins to move even faster towards the Earth…
faster shorterlonger
…then its absorption line pattern faster shorterlonger
…then its absorption line pattern will be even more Doppler shifted… faster shorterlonger
faster shorterlonger
faster shorterlonger …towards the blue end
…towards the blue end of the spectrum. faster shorterlonger
faster shorterlonger …towards the blue end of the spectrum.
faster shorterlonger …towards the blue end of the spectrum.
Compare all three.
no movement towards Earth Compare all three.
no movement towards Earth slow movement towards Earth Compare all three.
no movement towards Earth slow movement towards Earth fast movement towards Earth Compare all three.
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth It’s the same star
no movement towards Earth slow movement towards Earth fast movement towards Earth It’s the same star traveling towards the Earth,…
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth …but just moving
…but just moving at different speeds. no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth We know for sure
no movement towards Earth slow movement towards Earth fast movement towards Earth We know for sure that it’s the same star,…
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth …because it’s the same fingerprint pattern
no movement towards Earth slow movement towards Earth fast movement towards Earth …because it’s the same fingerprint pattern found in all (3) cases.
no movement towards Earth slow movement towards Earth fast movement towards Earth …because it’s the same fingerprint pattern found in all (3) cases.
no movement towards Earth slow movement towards Earth fast movement towards Earth …because it’s the same fingerprint pattern found in all (3) cases.
no movement towards Earth slow movement towards Earth fast movement towards Earth …because it’s the same fingerprint pattern found in all (3) cases.
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth The fact that the lines
The fact that the lines are blue shifted at all,... no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth …tells us that the star
…tells us that the star is moving towards the Earth. no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth But it’s the amount of blue shift,
no movement towards Earth slow movement towards Earth fast movement towards Earth But it’s the amount of blue shift, however,…
no movement towards Earth slow movement towards Earth fast movement towards Earth
no movement towards Earth slow movement towards Earth fast movement towards Earth …which reveals the star’s speed
no movement towards Earth slow movement towards Earth fast movement towards Earth …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth faster …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth faster …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth faster …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth slower faster …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth slower faster …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth slower faster …which reveals the star’s speed towards the Earth.
no movement towards Earth slow movement towards Earth fast movement towards Earth slower no motion faster …which reveals the star’s speed towards the Earth.
shorterlonger
shorterlonger Now imagine
shorterlonger Now imagine that the same star…
shorterlonger
shorterlonger …begins to move slowly
shorterlonger …begins to move slowly away from the Earth.
shorterlonger …begins to move slowly away from the Earth.
shorterlonger …begins to move slowly away from the Earth.
slowly shorterlonger …begins to move slowly away from the Earth.
slowly shorterlonger
slowly shorterlonger The absorption line pattern
slowly The absorption line pattern will now be Doppler shifted… shorterlonger
slowly shorterlonger
slowly shorterlonger …towards the red end
slowly shorterlonger …towards the red end of the spectrum.
slowly shorterlonger …towards the red end of the spectrum.
slowly shorterlonger …towards the red end of the spectrum.
shorterlonger
shorterlonger And if the star begins to move
shorterlonger And if the star begins to move even faster away from the Earth,…
shorterlonger And if the star begins to move even faster away from the Earth,…
shorterlonger And if the star begins to move even faster away from the Earth,…
faster shorterlonger And if the star begins to move even faster away from the Earth,…
faster shorterlonger
faster shorterlonger …then its absorption line pattern
faster …then its absorption line pattern will be even more Doppler shifted… shorterlonger
faster shorterlonger
faster shorterlonger …towards the red end
faster shorterlonger …towards the red end of the spectrum.
faster shorterlonger …towards the red end of the spectrum.
shorterlonger faster …towards the red end of the spectrum.
Once again,
Once again, let’s compare the (3) spectra.
no movement away from Earth Once again, let’s compare the (3) spectra.
slow movement away from Earth no movement away from Earth Once again, let’s compare the (3) spectra.
slow movement away from Earth fast movement away from Earth no movement away from Earth Once again, let’s compare the (3) spectra.
slow movement away from Earth fast movement away from Earth no movement away from Earth
slow movement away from Earth fast movement away from Earth no movement away from Earth It’s again the same star
slow movement away from Earth fast movement away from Earth no movement away from Earth It’s again the same star traveling away from the Earth,…
slow movement away from Earth fast movement away from Earth no movement away from Earth
slow movement away from Earth fast movement away from Earth no movement away from Earth …it’s just now traveling
slow movement away from Earth fast movement away from Earth no movement away from Earth …it’s just now traveling at different speeds.
slow movement away from Earth fast movement away from Earth no movement away from Earth
slow movement away from Earth fast movement away from Earth We know for certain
no movement away from Earth slow movement away from Earth fast movement away from Earth We know for certain that it’s the same star,…
no movement away from Earth slow movement away from Earth fast movement away from Earth
no movement away from Earth slow movement away from Earth fast movement away from Earth …because all (3) spectra
no movement away from Earth slow movement away from Earth fast movement away from Earth …because all (3) spectra have the exact same fingerprint pattern.
no movement away from Earth slow movement away from Earth fast movement away from Earth …because all (3) spectra have the exact same fingerprint pattern.
no movement away from Earth slow movement away from Earth fast movement away from Earth …because all (3) spectra have the exact same fingerprint pattern.
no movement away from Earth slow movement away from Earth fast movement away from Earth …because all (3) spectra have the exact same fingerprint pattern.
slow movement away from Earth fast movement away from Earth no movement away from Earth
The fact that the lines slow movement away from Earth fast movement away from Earth no movement away from Earth
The fact that the lines are red shifted at all… slow movement away from Earth fast movement away from Earth no movement away from Earth
slow movement away from Earth fast movement away from Earth no movement away from Earth
slow movement away from Earth fast movement away from Earth no movement away from Earth …tells us that the star
…tells us that the star is moving away from Earth. slow movement away from Earth fast movement away from Earth no movement away from Earth
slow movement away from Earth fast movement away from Earth no movement away from Earth
slow movement away from Earth fast movement away from Earth But it’s the amount of red shift,
no movement away from Earth slow movement away from Earth fast movement away from Earth But it’s the amount of red shift, however,…
no movement away from Earth slow movement away from Earth fast movement away from Earth
no movement away from Earth slow movement away from Earth fast movement away from Earth …which reveals the star’s speed
no movement away from Earth slow movement away from Earth fast movement away from Earth …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth faster …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth faster …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth faster …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth slower faster …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth slower faster …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth slower faster …which reveals the star’s speed away from the Earth.
no movement away from Earth slow movement away from Earth fast movement away from Earth slower faster no motion …which reveals the star’s speed away from the Earth.
The Doppler Effect
The Doppler Effect and Rotating Stars
The Doppler Effect
The Doppler Effect is also useful…
…in determining the rotations
…in determining the rotations of stars.
star’s north pole …in determining the rotations of stars.
star’s north pole …in determining the rotations of stars.
star’s north pole …in determining the rotations of stars.
star’s equatorstar’s north pole …in determining the rotations of stars.
Imagine that the Earth lies
Imagine that the Earth lies is in this direction.
This star’s motion
This star’s motion is stationary in space.
The star is not approaching
The star is not approaching the Earth,…
…but neither is it receding away
…but neither is it receding away from the Earth either.
But the star does spin on its axis
But the star does spin on its axis in a counter-clockwise direction.
counter-clockwise
But the star does spin on its axis in a counter-clockwise direction. counter-clockwise
But the star does spin on its axis in a counter-clockwise direction. counter-clockwise
The far left side
The far left side of the star…
…approaches the Earth
…approaches the Earth with the greatest speed.
So a spectral line
So a spectral line from this point on the star’s surface…
…would show the greatest amount
…would show the greatest amount of blue shift.
shorterlonger …would show the greatest amount of blue shift.
shorterlonger …would show the greatest amount of blue shift.
shorterlonger …would show the greatest amount of blue shift.
shorterlonger
But other places shorterlonger
But other places on left side of the star… shorterlonger
shorterlonger
shorterlonger …also approach the Earth
…also approach the Earth but at different speeds. shorterlonger
shorterlonger
For example, shorterlonger
For example, consider this position. shorterlonger
shorterlonger For example, consider this position.
shorterlonger For example, consider this position.
shorterlonger For example, consider this position.
shorterlonger
At this location shorterlonger
At this location on the star’s surface,… shorterlonger
shorterlonger
shorterlonger …the motion is more complicated
…the motion is more complicated than the previous position’s motion. shorterlonger
shorterlonger …the motion is more complicated than the previous position’s motion.
shorterlonger
Only some of its motion shorterlonger
Only some of its motion is towards the Earth,… shorterlonger
shorterlonger Only some of its motion is towards the Earth,…
shorterlonger Only some of its motion is towards the Earth,…
shorterlonger
shorterlonger …while the rest of it’s motion
…while the rest of it’s motion is lateral to our line of sight. shorterlonger
shorterlonger …while the rest of it’s motion is lateral to our line of sight.
shorterlonger …while the rest of it’s motion is lateral to our line of sight.
shorterlonger
Therefore, the spectral line shorterlonger
Therefore, the spectral line which is located at this position… shorterlonger
shorterlonger
shorterlonger …is not nearly as blue shifted
shorterlonger …is not nearly as blue shifted as much as the other one.
shorterlonger …is not nearly as blue shifted as much as the other one.
shorterlonger …is not nearly as blue shifted as much as the other one.
shorterlonger
shorterlonger Now consider a point
shorterlonger Now consider a point on the front side of the star.
shorterlonger Now consider a point on the front side of the star.
shorterlonger Now consider a point on the front side of the star.
shorterlonger
shorterlonger
Its motion at this location shorterlonger
Its motion at this location is lateral to our line of sight. shorterlonger
Its motion at this location is lateral to our line of sight. shorterlonger
Its motion at this location is lateral to our line of sight. shorterlonger
shorterlonger
shorterlonger So neither it is red shifted,
So neither it is red shifted, nor is it blue shifted. shorterlonger
shorterlonger
shorterlonger A spectral line from this location
shorterlonger A spectral line from this location will therefore be centered…
shorterlonger
shorterlonger …and show no Doppler shift
…and show no Doppler shift at all. shorterlonger
shorterlonger …and show no Doppler shift at all.
shorterlonger …and show no Doppler shift at all.
shorterlonger
A point which is located shorterlonger
A point which is located on the star’s right side… shorterlonger
shorterlonger A point which is located on the star’s right side…
shorterlonger A point which is located on the star’s right side…
shorterlonger A point which is located on the star’s right side…
shorterlonger
shorterlonger …will also demonstrate
shorterlonger …will also demonstrate complicated motion.
shorterlonger …will also demonstrate complicated motion.
shorterlonger …will also demonstrate complicated motion.
shorterlonger
Only some of its motion shorterlonger
shorterlonger Only some of its motion recedes away from the Earth,…
shorterlonger Only some of its motion recedes away from the Earth,…
shorterlonger
shorterlonger
…while the rest of it moves laterally shorterlonger
…while the rest of it moves laterally to our line of sight. shorterlonger
shorterlonger …while the rest of it moves laterally to our line of sight.
shorterlonger …while the rest of it moves laterally to our line of sight.
shorterlonger
A spectral line from this point shorterlonger
A spectral line from this point on the star’s surface… shorterlonger
shorterlonger
…will therefore be shorterlonger
…will therefore be only partially red shifted. shorterlonger
shorterlonger …will therefore be only partially red shifted.
shorterlonger …will therefore be only partially red shifted.
shorterlonger
Now consider shorterlonger
Now consider this final position. shorterlonger
shorterlonger Now consider this final position.
shorterlonger Now consider this final position.
shorterlonger Now consider this final position.
shorterlonger
shorterlonger The far right side
The far right side of the star… shorterlonger
shorterlonger
…recedes away from the Earth shorterlonger
…recedes away from the Earth with the greatest speed. shorterlonger
shorterlonger …recedes away from the Earth with the greatest speed.
shorterlonger …recedes away from the Earth with the greatest speed.
shorterlonger
shorterlonger Therefore, a spectral line
Therefore, a spectral line from this point on the star’s surface… shorterlonger
shorterlonger
shorterlonger …shows the greatest amount
…shows the greatest amount of red shift of all. shorterlonger
shorterlonger …shows the greatest amount of red shift of all.
shorterlonger …shows the greatest amount of red shift of all.
shorterlonger
shorterlonger So for this
So for this rotating star,… shorterlonger
shorterlonger
shorterlonger …should we expect to see
…should we expect to see only these (5) spectral lines? shorterlonger
shorterlonger …should we expect to see only these (5) spectral lines?
shorterlonger
shorterlonger No, because there are more
No, because there are more than (5) individual points… shorterlonger
shorterlonger
shorterlonger …on the star’s surface
…on the star’s surface which are rotating. shorterlonger
shorterlonger
shorterlonger All of the other points,
All of the other points, which we did not select,… shorterlonger
shorterlonger
shorterlonger …would fill in the rest of the spaces
…would fill in the rest of the spaces between the (2) extremes. shorterlonger
shorterlonger
shorterlonger So rather than having
So rather than having only (5) spectral lines in total,… shorterlonger
shorterlonger
shorterlonger …all of the points
…all of the points would now just blend together. shorterlonger
shorterlonger
shorterlonger So this would instead result
So this would instead result in one single broad bar. shorterlonger
shorterlonger So this would instead result in one single broad bar.
shorterlonger So this would instead result in one single broad bar.
shorterlonger
shorterlonger So the faster that the star rotates
So the faster that the star rotates on its axis,… shorterlonger
shorterlonger
shorterlonger …then the more red and blue shifted
…then the more red and blue shifted the points on its surface will become. shorterlonger
shorterlonger
And the more red and blue shifted shorterlonger
And the more red and blue shifted those points become,… shorterlonger
shorterlonger
shorterlonger …then the broader
…then the broader the bar also becomes. shorterlonger
shorterlonger …then the broader the bar also becomes.
shorterlonger …then the broader the bar also becomes.
shorterlonger …then the broader the bar also becomes.
shorterlonger
shorterlonger So a broad bar
shorterlonger So a broad bar indicates a fast rotation.
shorterlonger fast rotation So a broad bar indicates a fast rotation.
shorterlonger
shorterlonger But the slower the star rotates,
But the slower the star rotates, on the other hand,… shorterlonger
shorterlonger
shorterlonger …then the less red and blue shifted
…then the less red and blue shifted the points on its surface become. shorterlonger
shorterlonger
And the less red and blue shifted shorterlonger
And the less red and blue shifted those points become… shorterlonger
shorterlonger
shorterlonger …then the less broad
…then the less broad the bar also becomes. shorterlonger
shorterlonger …then the less broad the bar also becomes.
shorterlonger …then the less broad the bar also becomes.
shorterlonger …then the less broad the bar also becomes.
shorterlonger
shorterlonger So a narrow bar
shorterlonger So a narrow bar indicates a slow rotation.
shorterlonger slow rotation So a narrow bar indicates a slow rotation.
shorterlonger
shorterlonger And if the star
And if the star were to cease rotating all together,… shorterlonger
shorterlonger
shorterlonger …then the bar would reduce
…then the bar would reduce to one single spectral line. shorterlonger
shorterlonger …then the bar would reduce to one single spectral line.
shorterlonger …then the bar would reduce to one single spectral line.
shorterlonger …then the bar would reduce to one single spectral line.
shorterlonger
shorterlonger So the fact that the star’s spectral lines
shorterlonger So the fact that the star’s spectral lines are broad in the first place…
shorterlonger
shorterlonger …reveals that the star
shorterlonger …reveals that the star is spinning on its axis.
shorterlonger …reveals that the star is spinning on its axis.
shorterlonger shorterlonger …reveals that the star is spinning on its axis.
shorterlonger …reveals that the star is spinning on its axis.
shorterlonger spinning …reveals that the star is spinning on its axis.
shorterlonger
shorterlonger But it’s the amount of the spectral line’s
But it’s the amount of the spectral line’s red or blue shift,… shorterlonger
shorterlonger
…which reveals the speed shorterlonger
…which reveals the speed at which the star rotates. shorterlonger
…which reveals the speed at which the star rotates. shorterlonger
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger …which reveals the speed at which the star rotates. faster
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger …which reveals the speed at which the star rotates. slower
shorterlonger …which reveals the speed at which the star rotates.
shorterlonger
…which reveals the speed at which the star rotates. shorterlonger
shorterlonger
shorterlonger However, if the star rotated
However, if the star rotated while it also was approaching the Earth,… shorterlonger
shorterlonger
shorterlonger …then not only
…then not only would it’s bar be broad,… shorterlonger
shorterlonger …then not only would it’s bar be broad,…
shorterlonger …then not only would it’s bar be broad,…
shorterlonger …then not only would it’s bar be broad,…
shorterlonger …then not only would it’s bar be broad,…
shorterlonger
shorterlonger …but it would also be shifted
…but it would also be shifted towards the blue end of the spectrum. shorterlonger
shorterlonger …but it would also be shifted towards the blue end of the spectrum.
shorterlonger …but it would also be shifted towards the blue end of the spectrum.
shorterlonger
shorterlonger
But if the same star rotated shorterlonger
But if the same star rotated while it also was receding away from Earth,… shorterlonger
shorterlonger
shorterlonger …then not only
…then not only would it’s bar be broad,… shorterlonger
shorterlonger …then not only would it’s bar be broad,…
shorterlonger …then not only would it’s bar be broad,…
shorterlonger …then not only would it’s bar be broad,…
shorterlonger
shorterlonger …but it would also be shifted
…but it would also be shifted towards the red end of the spectrum. shorterlonger
shorterlonger …but it would also be shifted towards the red end of the spectrum.
shorterlonger …but it would also be shifted towards the red end of the spectrum.
shorterlonger
And the faster the star’s speed shorterlonger
And the faster the star’s speed either towards or away from Earth… shorterlonger
shorterlonger
…then the greater shorterlonger
…then the greater its red or blue shift would be. shorterlonger
shorterlonger
This would create an almost infinite shorterlonger
This would create an almost infinite number of combinations… shorterlonger
shorterlonger
shorterlonger …of possible bar broadnesses
…of possible bar broadnesses and red and blue shifts. shorterlonger
Review
shorterlonger
shorterlonger So not only can we determine
So not only can we determine that the star is rotating on its axis,… shorterlonger
shorterlonger
shorterlonger …but also thanks
…but also thanks to the Doppler Effect,… shorterlonger
shorterlonger
shorterlonger …we can also determine
…we can also determine how fast the star is rotating. shorterlonger
shorterlonger …we can also determine how fast the star is rotating.
shorterlonger …we can also determine how fast the star is rotating.
shorterlonger …we can also determine how fast the star is rotating.
shorterlonger
shorterlonger And not only can we tell a star’s motion
shorterlonger And not only can we tell a star’s motion either towards or away from Earth,…
shorterlonger And not only can we tell a star’s motion either towards or away from Earth,…
shorterlonger And not only can we tell a star’s motion either towards or away from Earth,…
shorterlonger And not only can we tell a star’s motion either towards or away from Earth,…
shorterlonger And not only can we tell a star’s motion either towards or away from Earth,…
shorterlonger And not only can we tell a star’s motion either towards or away from Earth,…
shorterlonger And not only can we tell a star’s motion either towards or away from Earth,…
shorterlonger
shorterlonger …but we can also determine
shorterlonger …but we can also determine the speed of that motion as well.
shorterlonger
And all of these motions shorterlonger
And all of these motions are detectable… shorterlonger
shorterlonger
…simply by using shorterlonger
…simply by using the Doppler Effect. shorterlonger
shorterlonger …simply by using the Doppler Effect.
shorterlonger …simply by using the Doppler Effect.
End of Part 4