What does it mean when an emission line of helium from a galaxy is shifted towards red?
It means the source is moving AWAY from the observer.
When the emission line of helium from a galaxy is shifted towards the red end of the electromagnetic spectrum, it is known as a redshift. This phenomenon occurs because of the Doppler effect. The Doppler effect causes a shift in the wavelength of light emitted by an object that is moving away from the observer. In the case of a redshift, the object is moving away from the observer, resulting in a longer wavelength and a shift towards the red end of the spectrum.
In the context of galaxies, a redshift indicates that the galaxy is moving away from us. This phenomenon can be explained by the expansion of the universe. As the universe expands, galaxies move away from each other, causing their light to be redshifted. The degree of redshift can be used to estimate the velocity at which the galaxy is moving away from us, as well as calculate the galaxy's distance from our perspective.