In: Physics
Determining a Star’s Velocity
(1) For “moving away,” a red ray of light moved from the star to Earth. Then a spectrum appeared in the bottom half of the screen. Which statement about the spectrum on the bottom relative to the spectrum of the stationary star is correct?(A)The two spectra are exactly the same. (B)The dark lines in the bottom spectrum are shifted to the right. (C)The dark lines in the bottom spectrum are shifted to the left. (D)There are more dark lines in the bottom spectrum.
(2)For “moving toward,” a blue ray of light moved from the star to Earth. Then a spectrum appeared in the bottom half of the screen. Which statement about the spectrum on the bottom relative to the spectrum of the stationary star is correct? (A)The dark lines in the bottom spectrum are shifted to the left. (B)The two spectra are exactly the same. (C)The dark lines in the bottom spectrum are shifted to the right. (D) There are more dark lines in the bottom spectrum.
(3)For “moving perpendicular,” a white ray of light moved from the star to Earth. Then a spectrum appeared in the bottom half of the screen. Which statement about the spectrum on the bottom relative to the spectrum of the stationary star is correct? (A)The dark lines in the bottom spectrum are shifted to the right. (B)The dark lines in the bottom spectrum are shifted to the left. (C)The two spectra are exactly the same. (D)There are more dark lines in the bottom spectrum.
(4)Drag the gray arrow so that it is pointing midway between horizontal and vertical, heading upward and toward the left. Extend it as far as it will go. What do you notice about the speed of the star as compared to the speed of the star relative to Earth? (A)The speed of the star is the same as the speed of the star relative to Earth. (B)The speed of the star is much less than the speed of the star relative to Earth. (C)The speed of the star relative to Earth is zero. (D)The speed of the star is much greater than the speed of the star relative to Earth.
(5) Drag the gray arrow so that it is pointing midway between horizontal and vertical, heading downward and toward the right. Extend it as far as it will go. What do you notice about the speed of the star as compared to the speed of the star relative to Earth? (A)The speed of the star is much greater than the speed of the star relative to Earth. (B)The speed of the star is the same as the speed of the star relative to Earth. (C)The speed of the star relative to Earth is zero. (D)The speed of the star is much less than the speed of the star relative to Earth.
(6)Drag the gray arrow so that the star is moving directly to the right. What do you notice about the speed of the star as compared to the speed of the star relative to Earth? (A)The speed of the star is much greater than the speed of the star relative to Earth. (B)The speed of the star is much less than the speed of the star relative to Earth. (C)The speed of the star is the same as the speed of the star relative to Earth. (D)The speed of the star relative to Earth is zero.
The question is not clear in many ways. However, here are the concepts.
A star moving away from the observer (say on Earth) will have its emitted light red-shifted (move to lower frequency), i.e., the spectrum moving to left if we consider the intensity of light is plotted as a function of frequency with the frequency increasing from left to right.
A star moving towards the observer (say on Earth) will have its emitted light blue-shifted (move to higher frequency), i.e., the spectrum moving to the right if we consider the intensity of light is plotted as a function of frequency with the frequency increasing from left to right.
A star moving perpendicular to the observer (say on Earth) will have its emitted light will not change with respect to the spectrum of the stationary star.
These are due to the Doppler effect, the equation of frequency detected by the observer as
where , v the relative velocity of the moving source (the star here), fs is the frequency of light emitted by the source.
Please specify what the gray arrow represent in the question. It seems these are questions based on some computer software, so please specify what does moving the arrows do and on what are the arrows moved.