What is light? • Light is a form of electromagnetic radiation that travels in waves. • Most forms of EM radiation are invisible. • Light waves do not need a medium like water or air to travel through. Empty space is fine.
Electromagnetic Radiation • Every object in the universe emits some kind of radiation. • The wavelength of light determines the characteristics of each form of radiation.
If you listen to music on the radio = radio wave radiation. • If you use a microwave = microwave radiation 3. Military & police may use infrared goggles to see body heat in the dark = infrared radiation
4. Visible light lets us see color. 5. An example of Ultra-violet radiation is a sunburn. 6. If you have an x-ray taken = x-ray radiation. 7. Radioactive materials emit Gamma ray radiation.
Visible Light and the Prism • Visible white light is made up of various colors as seen in a rainbow. • When sunlight passes through a prism, the waves are refracted (bent) and a rainbow called a spectrum is produced.
Spectroscope • A tool astronomers use to separate starlight into a spectrum. • A prism is inserted into a telescope to split the light into its colors.
The spectroscope can tell astronomers... • What a star is composed of • How hot a star is • How fast a star or galaxy is moving • The direction a star or galaxy is moving
Continuous • An unbroken band of colors • The source emits light of all visible wavelengths
Unevenly spaced lines of different colors. The source emits light of certain wavelengths. (l) Every element has a unique emission spectrum. Emission
Absorption • A continuous spectrum crossed by dark lines. • Determines elements in cool gases.
Argon Helium Mercury Sodium Neon Each element has a unique spectrum. • By observing the spectra of distant stars we learned what elements make up the atmosphere of stars (and planets).
Sound • Think about the sound a train makes as it approaches you compared to when it moves away from you.
There is a change in the pitch of the sound. • High pitch sounds have a short wavelength • Low pitch sounds have a long wavelength.
What is the Doppler Effect? • The shift in the wavelength produced by a moving source. • The change in pitch as something approaches you and moves away from you.
Light • Light with a long wavelength will appear red. • Light with a short wavelength will appear blue.
Approaching light = blue • Leaving light = red
Red Shift Sun Galaxy • A star or galaxy moving away from the Earth will produce a shift in its spectrum towards the red end.
The Big Bang Theory • Red shifts are evidence supporting the Big Bang. • It’s the dominant scientific theory about the origin of the universe • The universe was created sometime ~ 10-20 billion years ago from a cosmic explosion that hurled matter in all directions.