Why are things blue shifted and not violet shifted?

  • Context: Undergrad 
  • Thread starter Thread starter Entropee
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Discussion Overview

The discussion revolves around the terminology used to describe the phenomenon of redshift and blueshift in relation to the motion of objects in space. Participants explore why objects moving towards an observer are referred to as blue shifted rather than violet shifted, touching on concepts of frequency and color perception.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that the terms "blue" and "red" are merely labels indicating shifts in frequency, not necessarily tied to the visible spectrum.
  • One participant notes that blue-shifted objects can emit wavelengths outside the visible spectrum, such as infrared.
  • Another participant expresses confusion about the relationship between color perception and the order of colors in the spectrum, specifically referencing the visible spectrum's arrangement.
  • There is a mention of the distinction between violet as a spectral color and purple as a perceptual color, highlighting a misunderstanding among participants.
  • Some participants question the implications of acceleration on wavelength, indicating a lack of clarity on the topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the terminology and its implications, with multiple competing views and some confusion remaining about the concepts discussed.

Contextual Notes

There are unresolved assumptions regarding the definitions of colors and their relationship to frequency shifts, as well as the impact of acceleration on wavelength.

Entropee
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If objects are moving away from us, they are known as red shifted, so why are objects moving towards us blue shifted and not violet shifted?
 
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Semantics. Blue-shifted objects are not necessarily blue: an object emitting at 5 um moving towards us is still blue shifted even though it is way outside the visible spectrum.
 
Entropee said:
If objects are moving away from us, they are known as red shifted, so why are objects moving towards us blue shifted and not violet shifted?

"blue" and "red" are just labels used to denote upshift or downshift in frequency.
 
Oh ok, yeah I just thought it was odd since most elemtary school students even know that purple comes after blue using roygbiv. Thanks :]
 
Entropee said:
If objects are moving away from us, they are known as red shifted, so why are objects moving towards us blue shifted and not violet shifted?

I didn't know that.

So acceleration of the object in relation to us alter wave length?

:eek:
 
Impagliazzo said:
I didn't know that.

So acceleration of the object in relation to us alter wave length?

:eek:

What? Entropee said nothing of the kind.
 
Entropee said:
Oh ok, yeah I just thought it was odd since most elemtary school students even know that purple comes after blue using roygbiv. Thanks :]
Actually, purple is not the same as violet. Violet is a spectral color consisting of wavelengths shorter than blue, but purple is a perceptual color seen only when both blue and red wavelengths are present.
 
Oh lol, my bad, I guess it's time for me to go back to Elementary school?
 
ideasrule said:
What? Entropee said nothing of the kind.

But what he said is right?

I want to know why!

Edit: Ok so I guess I just got pretty inventive with lack of clear information. LOL
 
Last edited:

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