1. The Electro-Magnetic Spectrum

2. Light Properties  Have properties of waves… Crests & troughsCrests & troughs Reflect & refract (bend)Reflect & refract (bend)  …and particles Can travel through spaceCan travel through space

3. EM Waves  The Speed of Light = c = 3 x 10 8 m/s (1.9 miles/second) = 3 x 10 8 m/s (1.9 miles/second)  Travels around the world about 8 times in one second c=  = frequency & = wavelength  Frequency = Hertz (Hz)=1/ second  Wavelength is a length – m to nm

4. EM Spectrum  Spectrum means “a range”  EM spectrum ranges from long wavelengths to short

5. Wavelength and Frequency  Wavelength is the distance between two peaks (or troughs)  Frequency is how frequently the waves occur  A longer wavelength means a lower frequency  A shorter wavelength means a higher frequency www.nasa.go v

6. Energy  As frequency decreases, energy increases  E = h h = 6.626 x 10 -34 Joules *secondh = 6.626 x 10 -34 Joules *second  Higher energy = high frequency = short wavelength!! Frequency Energ y

7. Light as a Particle  Light = photons  Photons are considered to be both particle and a wave  What does that mean? A photon is a “wave packet”A photon is a “wave packet” A photon is a “light particle”A photon is a “light particle”

9. The Visible Spectrum violet380-420 nm indigo420-450 nm blue450-495 nm green495-570 nm yellow570-590 nm orange590-620 nm red620-750 nm

10. Visible Light  Not all animals see the same wavelengths as humans  Some see shorter wavelengths (ultraviolet) HummingbirdsHummingbirds BeesBees  Others see longer wavelengths (infrared) BatsBats SnakesSnakes

11. Visible Light vs. UV Flower in visible light Flower in UV light

12. Visible Light vs. Infrared Bats in infrared light Bats in visible light

13. Full Visible Spectrum Red Orange Yellow Green Blue Violet (Indigo) (Indigo)

14. What does this have to do with Astronomy??

15. Two Girls in the IR Is this in “true color?” http://en.wikipedia.org/wiki/Infrared

17. How do we know what a star is made of??  By looking at its EM spectrum  The star’s “fingerprint” Hydrogen

18. How light or electromagnetic radiation is used in Astronomy Astronomers use spectroscopes separate starlight into its colors Identify star’s composition, temperature, luminosity Different wavelengths provide different information Temperature – Blackbody Radiation Composition – Absorption Spectrum Luminosity/Brightness

19. Emission Spectra Full spectrum Wavelengths: H

20. Models of a Hydrogen Atom  PhET's Model of a Hydrogen Atom PhET's Model of a Hydrogen Atom PhET's Model of a Hydrogen Atom