Green Stretch

Why is there no green shift in space?

If the expansion of the universe makes the wavelength of light stretch (to appear red) why is it not sometimes green when it reaches Earth?

You mean are there wavelengths that weren’t green, but were shifted to become green?

Sure, that happens. You could have a wavelength of 450 nm (blue) that gets shifted to 500 nm (green). That’s a red-shift of 50 nm.

The names “red shift” and “blue shift” don’t refer to the color of the received electromagnetic energy. Much of the EM energy isn’t visible light at all. These terms just mean “shifted to longer wavelength” or “shifted to shorter wavelength”. Those are the only possible directions, longer or shorter.

So in my example, you have a wavelength shifted to become green, but it’s STILL a red shift. And you could have a wavelength of 600 nm shifted to 500 nm (green) and that’s a blue shift.

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