So, how can Doppler Shifts help us know something about our universe?

Visible light, x-rays, radio waves and ultra-violet rays are all different forms of electromagnetic radiation, which also moves in waves. Scientists have learned that the electromagnetic radiation given off by a moving object exhibits Doppler Shifts, similar to changes in sound waves described above.

Electromagnetic waves moving toward an observer are squeezed together so their frequency appears to increase. Instead of the light getting higher in pitch as the frequency increases, the light is said to be “blue shifted.” This is because the blue end of the light spectrum is higher in frequency than the red end. If an object is moving away from an observer, light waves emitted by the object are stretched and the frequency decreases, causing a “red shift.”

Doppler shifts of radiation emitted by stars and other celestial objects have been very helpful in determining the movement of these objects with respect to our location in space. In the past, astronomers’ research involved the study of visible light, but today almost all parts of the electromagnetic spectrum are used to detect Doppler effects.

Astronomers can use red- and blue-shifts to calculate exactly how fast stars and other objects move away from and toward the Earth. An example of this involves the light emitted by hydrogen gas in distant galaxies. An important spectral line for hydrogen is found in laboratories here on Earth to have a wavelength of 21 centimeters. That means that the distance from one wave crest to the next is 21 centimeters, which is about the width of an ordinary piece of paper. If hydrogen from a distant galaxy is observed to have a wavelength of 21.1 centimeters, we would call this a red shift of 0.1 centimeter. Astronomers use mathematical equations to calculate that the galaxy is moving away from us at more than 1,400 kilometers per second.

In 1929, Edwin Hubble, an American astronomer, made one of more astounding discoveries in modern cosmology. He found that the entire universe is expanding. Hubble made measurements of galactic distances and used the Doppler Shifts to show that many of the galaxies were moving. In fact, they were speeding away from the Earth, as indicated by the red Doppler Shifts. Structures that are widely separated from each other, such as galactic clusters, are moving away from each other, increasing the distance between them with each passing moment of time.