1. Which color of visible light has the shortest wavelength?
(3) yellow
(2) green (4) red
(1) violet

2. Stars radiate electromagnetic energy.
We see this energy as light.
What happens to the light as the star moves?

3. “[A scientist] naturally and inevitably … mulls over the data and guesses at a solution...”

4. Distant objects are moving away quickly.
Their light waves “stretch out” and get longer. The colors SHIFT RED.
Some objects move toward us quickly “squeezing” color waves. They SHIFT BLUE.
Observer

5. Spectral lines of an element

6. Astronomers viewing light from distant galaxies observe a shift of spectral lines toward the red end of the visible spectrum. This shift provides evidence that
(1) orbital velocities of stars are decreasing
(2) Earth’s atmosphere is warming
(3) the Sun is cooling
(4) the universe is expanding