Epic of Evolution  
 

Redshift shows that the universe is expanding.

 

Looking at Rainbows to See the Universe Universe

Summary: When we look at rainbows, we are looking at white light split into its component colors, or spectrum. The study of light spectra is called spectroscopy. Looking at these rainbows of light can tell us about our evolving universe: what stars and galaxies are made of, how far away they are, and how fast they are moving. In this activity, we use diffraction glasses to observe how light is split into a rainbow of colors.

Age level: 7 to adult.

Time: 20 minutes.

Student Learning Outcomes:

  • Students will observe how light can be separated into various colors.
  • Students will learn how spectroscopy can be used to observe different elements
  • Students will learn how spectroscopy can be used to observe different elements from far off stars.
  • Students will learn that this characteristic of light helps us learn about the evolution of stars, galaxies, and the universe.

Introduction:

How old is the universe? What evidence is there for the Big Bang? What are stars and galaxies made of?

All these different questions can be answered by looking at rainbows.

A powerful tool for learning about the evolution of our universe is observing the the rainbows of light given off by stars and galaxies. The rainbow pattern formed by light of different sources is called a spectrum. Spectroscopy is the analysis of the light spectrum. Since stars and galaxies give off light, much can be learned about them through the study of spectroscopy.

Looking at the spectra of light that stars and galaxies give off, scientists have observed some interesting things.

Spectroscopy tells us what stars and galaxies are made of.

Since different kinds of materials have slightly different spectra, scientists can use a star's spectrum to figure out what it is made of.

Spectroscopy tells us about the position and movement of stars and galaxies.

Spectroscopy can also be used to tell us about the distance and movement of stars and galaxies. By observing the spectra of galaxies, scientists have discovered that some are moving away from us. Spectra from some galaxies appear to be redshifted. Red is a slower the frequency of light which has a longer wavelength. Objects moving away appear to have longer wavelenths, and hence have a redshift. The greater the redshift, the faster a galaxy is moving away from us. Furthermore, the faster a galaxy is moving away from us, the further away that galaxy is.

By observing redshifts, scientists are able to show that the universe is expanding, which is important evidence for the Great Radiance (a.k.a. Big Bang.) This redshift is the basis of Hubble's Law, which states that the degree of redshift in light is proportional to its distance from us. That is, the more red-shifted a galaxy is, the farther away it is.

 

Spectral lines of the sun (left) shift toward red in a supercluster of distant galaxies (right). The further away a galaxy is, the faster it moves away from us. This is detected as a redshift. Hence, in stars moving away from us, the spectral lines appear to shift in the direction of red.

 

Materials

Per Student:

  • Defraction grating glasses
  • Discarded CD's

Per Class:

  • Various light sources: neon light bulb, incandescent bulb,

Directions:

Look through glasses at various light sources. CAUTION! Do not look at any source of light that you would not look at without the glasses (ie sun).

  • Try looking at city lights
  • Traffic lights
  • Incandescent lights.

Spectra from Lights

Background:

Although we can see the spectrum of lights using diffraction glasses, we will not be able to see the redshift of galaxies using these glasses. To see the Red Shift of distant stars, scientists use more sensitive instruments to examine light spectra. Different elements absorb light in different frequencies, which causes dark bands to appear in the spectra. To the left is a picture with the spectra from various light sources.

Helium was discovered through spectroscopy. This element was not first discovered on Earth; it was first first discovered on the sun!

Resources:
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