Cosmic Colors: Doppler Shift Explained Quiz

If the distance between a light source and an observer is changing over time, and if light behaves as a wave, then the waves will be compressed or stretched depending on the direction of that motion.

If a source moves toward an observer, the waves are compressed into shorter wavelengths; if blue light has shorter wavelengths than red light, then the shift must be toward the blue end (blueshift).

If light travels as a wave, then it has a measurable spatial period; if we measure from one crest to the next, then that specific measurement is the wavelength.

If sound is a mechanical wave requiring a medium and light is an electromagnetic wave that can travel through a vacuum, then the underlying wave type is different, even though the shift principle is similar.

If the Doppler effect is a velocity-dependent phenomenon, then higher speeds cause greater shifts; if the direction determines the wave compression or expansion, then toward-motion must be blue and away-motion must be red.

If modern spectrographs are highly sensitive, then they can detect even tiny shifts caused by objects moving at a few meters per second; therefore, a high fraction of light speed is not required for detection.

If "red" light is at the long-wavelength end of the visible spectrum, and if an object moving away stretches the light it emits, then a redshift indicates the waves have been elongated.

If a blueshift represents a decrease in wavelength, and if decreasing wavelengths result from the source catching up to its own emitted waves, then the source must be moving toward the observer.

If elements absorb light at specific, known wavelengths, and if we see those known patterns shifted from their "rest" positions, then we can calculate exactly how fast the star is moving.

If Doppler shift only measures "radial velocity" (motion toward or away), then any object with a component of motion along our line of sight will show a shift, while perfectly sideways or circular motion will not.

If the Doppler effect only measures how fast an object is moving toward or away from us (velocity), then it provides no direct information about how far away that object currently is (distance).

If we need to see the individual "markers" or absorption lines to measure their displacement, then we must use a device that disperses light into its component colors, which is a spectrograph.

If the magnitude of the Doppler shift is directly proportional to the radial velocity of the source, then a larger shift mathematically requires a higher speed of motion.

If the Doppler effect describes shifting toward the "ends" of the visible spectrum, and if those ends are defined by red (approx. 700 nm) and blue/violet (approx. 400 nm), then these are the relevant colors.

If the speed of light in a vacuum is a universal constant (c), then the speed of the source does not change the speed of the light; instead, it changes the frequency and wavelength of that light.

If scientific convention defines "recession" as moving away, and if moving away is represented as a positive radial velocity, then a redshift is associated with a positive velocity value.

If wavelength is the distance between peaks, and if we count how often those peaks arrive over time, then the resulting value is the frequency of the wave.

If an orbiting planet pulls on its star, and if that pull makes the star move toward and away from Earth in a cycle, then the resulting pattern of blueshifts and redshifts reveals the planet's presence.

If the Doppler effect applies to all electromagnetic radiation, and if radio, X-rays, infrared, and microwaves are all forms of light, then they all experience shifts, whereas sound is a different type of wave.

If the universe is expanding, and if expansion moves distant galaxies away from us in all directions, then the light from those galaxies must be stretched into longer wavelengths (redshifted).