Investigative Science – RED SHIFT BLUE SHIFT Friday January 20, 2017 Perry High School Notebook page: 11 Mr. Pomerantz______Page 1 of 2 Directions: Read, annotate and completely answer the prompt using 100 words or less. One Shift, Two Shift, Red shift, Blue shift. Adapted from: https://sciencedecrypted.wordpress.com/2014/03/22/oneshifttwoshiftredshiftblushift/

Red shift and blue shift are amazing physical phenomenon that are one of the greatest tools to astronomy. They allow us to study the stars and galaxies and unlock the secrets of the universe. What are redshift and blue shift? They are the increasing and decreasing of the wavelength of electromagnetic radiation. Now that probably doesn’t mean much of anything to you so let’s look at it piece by piece. Have you ever heard a train or ambulance passing by you and noticed how when it passes you the sound of its horn or siren immediately sounds different? This is what is known as the Doppler Effect. As the train is moving towards you the sound waves that are coming from it are compressed. Once the train passes you, it is moving away from you and now the sound waves are stretched out. This stretching and compressing of the sound waves causes the pitch to change as well, which is the reason for the two different sounds you hear when a train is moving towards and away from you.

Doppler Effect Electromagnetic radiation is a type of wave as well, albeit very different from sound waves, but the Doppler Effect still applies. The electromagnetic spectrum is the range of wavelengths that electromagnetic radiation can possess, and includes, radio waves, infrared, x-ray’s, and visible light, what kind of wave it is depends upon its wavelength.

Radio waves have the longest wavelengths, visible light is in the middle, and gamma rays have the shortest wavelengths. Now within the visible light spectrum are all the different wavelengths that you and I perceive as colors. Red is at the begging of the spectrum and has the longest wavelengths. Blue which is near the end of the spectrum and has shorter wavelengths.

Applying the Doppler Effect to visible light, say yellow for example. As a yellow object moved closer to you its wavelength would become compressed and become shorter, so it is said to be blue shifted. If the yellow object was moving away from you its wavelength would get stretched and its wavelength would become longer, so it is said to be red shifted. The speeds we deal with in everyday life aren’t fast enough to cause a noticeable effect on light, so a yellow car moving away from you would still be red shifted, but not nearly enough for the yellow light coming off it to turn red, so the car still appears yellow. However, in astronomy where scientists deal with much faster speeds, greater distances, and more precise measuring instruments than our eyes, you can see noticeable effects.

So how do astronomers observe redshift and blue shift? They look at Emission spectrums. When astronomers look at astronomical bodies like stars they look at the emission spectra’s. If the emissions are redshifted then the lines you see will be shifted towards the red end, and for blue shifted bodies well I think you get the picture.

So why are redshift and blue shift so important to astronomy? That’s because with red shift and blue shift astronomers can study many things about the universe. One of the earliest uses of red shift was in 1929 when a young astronomer named Edwin Hubble used redshift to make the discovery that the universe was expanding. This was a big revelation because at the time most physicists and astronomers (including Einstein) believed that the universe was static, that it was neither expanding nor contracting and that the universe was eternal, that it had always existed. Hubble’s discovery also gave a lot of credit to the Big Bang theory.

The discoveries that the universe is expanding and that that expansion is accelerating means that almost everything in the universe is redshifted.

Redshift allows us to measure the distance of stars and galaxies, how old they are and how fast they’re moving away from us. The amount of redshift an electromagnetic wave has is proportional to the distance it has traveled. This is known as Hubble’s law and using this law astronomers can use red shift to calculate the time it took the light to reach us, the distance of the object emitting the electromagnetic radiation, how fast it is moving away from us.

Redshift also has applications to us non-astronomers too. If you’ve ever gotten a speeding ticket before, you can thank redshift. When a police officer fires a radar gun at your car, he fires radio waves. When the radio waves hit your car, they are reflected to the radar gun. Using your car as the source of the radio waves the gun can detect the amount of redshift that has occurred in the waves from your cars movement and use that to determine your cars speed.

Using a similar technique, you can measure air current velocities in the atmosphere. This is what Weatherman and Meteorologists refer to as Doppler radar and it is a very useful tool for studying and predicting the weather. Investigative Science – RED SHIFT BLUE SHIFT Friday January 20, 2017 Perry High School Notebook page: 11 Mr. Pomerantz______Page 2 of 2 Prompt: The concepts of a red shift, blue shift and the Doppler effect can be complicated. In 100 words or less, explain how the author of the article One Shift, Two Shift, Red shift, Blue shift (above) discusses what red and blue shifts are and how they have been used by Edwin Hubble to prove that the universe is expanding. Use specific content from the article when possible and appropriate.