How does the red shift work?

Question

While the spectral line of an element moves toward red, how do scientists know that they are looking at the same element, to conclude that it is moving away from the earth?

Answer 1

The way the red shift works is that an object moving away from you emits a photon farther away from the previous photon. It is like the pulses of sound coming from a train as it moves past you. Each pulse of sound is emitted further away from the previous pulse. Since frequency is the time between the peaks of a light wave and red has a lower frequency than other colors we can see, it is called the red shift. Each element has a specific pattern of wavelengths it emits so the scientists studying the wavelengths can tell that the same element is emitting light at a lower frequency.

Answer 2

"...how do scientists know that they are looking at the same element..."

Hundreds of years of laboratory research has well established the distinctive spectral pattern of all known elements. These same spectra can be observed from distant objects, only the distinctive patterns will be shifted left or right. From the direction and amount of shift the velocity of the distant object can be derived.

Answer 3

Elements have very distinct emission/absorbtion spectra patterns. If those lines appear somewhere other than the frequency at which you expect them, they aren't another element; it's hydrogen shifted.

There's a great image in the Wikipedia:
http://en.wikipedia.org/wiki/Emission_spectrum

Answer 4

Since more than 90% of all matter is hydrogen, the hydrogen lines are by far the easiest to detect and most prominent in any spectrogram. The most prominent single line in a galactic source is always hydrogen alpha, and that's what they measure.

Answer 5

It is something akin to the Doppler Effect. The light waves grow longer with the speed the object retreats from us.