Do receding galaxies LOOK redder than they really are?

Question

It seems to me that, within limits, a galaxy emits light through the entire visible spectrum (except where occur absorbtion bands). I would think that each color, in turn, would become invisible to us, but another wavelength would take it's place and the galaxy would have a normal appearance. In other words if something is emitting ultraviolet through infrared radiation is receding at the proper velocity ultraviolet would become violet, and orange would become red, and the others in between would "move one notch" so to speak, leaving the object looking normal to us. Wouldn't radio wavelengths eventually become visible if the velocity of recession was correct?

Answer 1

You could be right in some instances. If a galaxy was emitting equal amounts of light at different frequencies, it could look white to us. But when we looked at the white light with a spectragraph we can tell that it was ultraviolet when it was emitted from the spacing of the spectral lines.
Most galaxies emit mainly white light, so they do look red when Hubble spies on them.

Answer 2

Yes. The part of your question that you asked and nobody answered is that light is not given off equally by galaxies at all frequencies. If you look at the light from a star and separate the frequencies ( this is what spectroscopy is all about) you will notice that some frequencies appear and some don't. Since stars are mostly hydrogen the emission spectra of hydrogen gives us most of the information. When an electron in a hydrogen atom transitions from one state to the ground state, it emits a photon with a very specific frequency. When a star from a galaxy is moving away from us that very specific frequency is shifted. As long as the shift is relatively small so that we can guess which hydrogen emission line it belongs to, we can estimate the shift from where it would be if it were not moving and therefore compute the star's velocity.

Answer 3

That would be true, if every band of energy were equal, or nearly so. In actuallity, the light emitted in different bands is of greater or lesser magnitude than the ones around it. That doesn't mean that we'll see visibly a different color, but that the wavelenghts of emitted energy are shifted toward the red end of the spectrum enabling optical instruments to determine the degree to which the galaxy is travelling away from us.
The actual shift isn't really enough to see with the eye, but only with carefully calibrated instruments. Radio wavelengths wouldn't become visible because they are much lower in frequency than is light.

Answer 4

Because the quantity of light tails off at higher frequencies, there is no light sufficiently beyond the violet to move into violet once the recession speed reaches a certain level. So they must look redder.

Check out the curve for black body radiation and Wien's law.

Answer 5

The light does change color. You can only see it with instruments because your eye is not sensitive to color in dim light. Getting it down to radio wavelengths would require a lot of speed. The only galaxies moving fast enough are very far away.

Answer 6

Yes. You are correct. Receding galaxies appear more red than they really are. This is called the Doppler Effect. Hubble and others used the "red shift" to measure the distance and speed of the receding galaxies.

Answer 7

You're sort of right about the replacing of wavelengths. It wouldn't look exactly the same, though, because of differing intensities of different wavelengths.

In order for us to see radio wavelengths visibly, they would have to be highly blueshifted, not highly redshifted. They're already way longer than visible, blueshifting them by several orders of magnitude would make them fall into the visible spectrum.

Answer 8

No they would have to be coming TOWARDS us with quite a speed to move into the red spectrum.

Answer 9

measuably redder yes, but not noticable to the naked eye