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I have to research this topic for a school project and nothing is showing up other than redshifts and blueshifts and Doppler shifts.

Are these all under the spectral shift category? Is a spectral shift just when light from a galaxy shifts towards one or the other end of the light spectrum? Please help.

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    You might do better at the astronomy stack exchange – Organic Marble Jan 03 '24 at 20:34
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    You also may need to give more context about what the topic says. Is it just the words "spectral shift" and nothing else? – Darth Pseudonym Jan 03 '24 at 21:13
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    spectral shift is an ambiguous term and in this case without context, will be difficult to answer. Consider that one can make reference to visible spectrum and limit the answer to only those frequencies. The same applies to the various RF bands such as microwave radiation, x-rays, UHF, etc. The spectral shift of a radar band frequency after contacting the target is used to determine location and velocity. Narrow your question or re-phrase it to encompass as appropriate. – fred_dot_u Jan 03 '24 at 22:09
  • you could also consider including a quote or some material where you've seen the phrase "spectral shift" used. I think it's not a clearly defined expression at all. If I saw it I would continue reading to see exactly what they could be talking about. Was there an intense magnetic or electric field? Or a velocity? Or a gravity gradient? Autotune? Breathing helium? – uhoh Jan 05 '24 at 00:43

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Answer: Spectral shift is systematic displacement of the spectrum due to relative motion of the observer relative to the emitter.

A hot body (such as the sun) emits light over a broad range of frequencies. If this light is spread out into a continuous spectrum with a prism, the relative intensity of light in each colour is characteristic of the temperature of the emitting surface.

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Although the spectrum is a continuous “rainbow”, very specific “signpost” lines can appear where gas molecules have interacted with light at that exact frequency. The lines can be either dark (where the atom has absorbed light from passing light)

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or bright (where an excited atom has emitted light).

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But in either case, the position of the lines (and their relation with each other) are absolutely characteristic of the molecule, and independent of the distance between source and observer.

However, if the source and observer are moving towards each other, all the lines will be shifted towards higher frequency (“blue shifted”). If the source and observer are moving away from each other the lines will be shifted towards lower frequencies (“red shifted”).

This effect was first described by Christian Doppler in 1842 and is referred to as “Doppler shift”

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If the observer can identify the emitting molecule from the pattern of lines, the red (or blue) shift can reveal the relative velocity of source and observer as well as the chemical makeup of the emitter.

Illustrations from Wikipedia

Woody
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