Forgot about Blue Shift. I work as a paint color matcher and green is always considered the opposite of red. But it's interesting to note that red shift is not universal!Borg said:It is referred to as a Blue Shift. However, the shift would be minor.
The Andromeda Galaxy's blue shift due to its eventual collision with the Milky Way is one of the few. It is pretty minor compared to really distant objects when talking about red shift.Yolander said:Forgot about Blue Shift. I work as a paint color matcher and green is always considered the opposite of red. But it's interesting to note that red shift is not universal!
The galaxies in our local group are close enough to be held together by their mutual gravitational attraction and are not effected by the expansion of the universe. To put it another way, galaxies form clusters that hold together and it is these clusters that are moving apart from each other.Yolander said:Forgot about Blue Shift. I work as a paint color matcher and green is always considered the opposite of red. But it's interesting to note that red shift is not universal!
Yup I totally had a brain cramp knowing that compression of light wavelength moves toward ultra violet on the spectrum, sorry.mathman said:The use of the terms "red" and "blue" refer to the direction of the shift (red - lower frequency, blue - higher frequency). It has nothing to do with the colors as colors.
ebos said:Is there a reason they stop at blue?
I think it's just a convention that was arrived at because of the historical notion of 'primary colors', as used by artists.ebos said:I've always wondered why light that moves towards us isn't called 'violet-shifted' (or indigo or green etc.). Is there a reason they stop at blue?
ebos said:I've always wondered why light that moves towards us isn't called 'violet-shifted' (or indigo or green etc.). Is there a reason they stop at blue?
The original astronomers were only using optical telescopes and the limit of the distances they could observe was such that the detectable shifts were very much in the optical region (with some spillage over into IR, I guess) So the terms are based on history. But that goes for many of the phrases used in Science. I can be a waste of effort to worry too much about such things.rootone said:it wouldn't be illogical to refer to 'X-ray frequency shifted' or 'radio frequency shifted',
rootone said:it wouldn't be illogical to refer to 'X-ray frequency shifted' or 'radio frequency shifted',
This is the phenomenon on which red shift is actually measured in practice. Looking at the peak of the spectrum of a hot object is a hopelessly inaccurate way of assessing speed of recession. What is normally used is detailed spectral analysis of the light received and the line spectra of individual elements in the gases surrounding stars is used. Normally, I believe, they use the absorption spectrum of those gases -very narrow absorption lines due to Hydrogen etc atoms, through which the star's light is shining can be identified. The relative positions of the characteristic spectral lines can be seen (the fingerprint of the element) but all the lines will be shifted. The amount of that shift will give an accurate measure of the amount of red shiftrbelli1 said:Now what happens when a narrow spectrum high energy object gets red shifted into the purple? What do we call that?