1. CHAPTER 3 (p. 62-68) Light

2. Only a very small range of wavelengths, 400nm to 700nm, are visible to humans. Wavelengths are very small so astronomers use nanometers 10 -9 m or angstroms 10 -10 m Electromagnetic Radiation

3. CRAB NEBULA OpticalUltra Violet X-RayRadio

4. Multiwavelength Universe

5. The transparency of a material depends on the wavelength of light. Earth’s atmosphere is relatively transparent to visible light and radio waves, which are referred to as “windows” through which we can view space from a ground-based telescope.

6. l l Gamma-rays more than 10 8 (K) accretion disks around black holes l l X-rays 10 6 -10 8 K gas in clusters of galaxies, supernova remnants; stellar corona l l Ultraviolet 10 4 -10 6 K supernova remnants; very hot stars l l Visible 10 3 -10 4 K planets, stars, some satellites l l Infrared 10-10 3 K cool clouds of dust and gas; planets l l Radio less than 10 K radio emission produced by electrons moving in magnetic fields Radiation TypeTemp. Source

7. Electromagnetic radiation Oscillations of electric and magnetic fields Inseparable – move in same direction Move through empty space at the speed light (c) c= 3.0 x 10 8 m/s

8. Models of Light Wave Model l l Behaves as a transverse wave l l Described by wavelength, frequency and amplitude l l Explains how light waves interfere with each other

9. The Doppler Effect Sources moving toward the observer squeeze light waves in front of them, causing them to be shorter. We call this a blueshift. Sources moving away from the observer stretch the light waves behind them, causing them to be longer. We call this a redshift.

10. Models of Light Particle Model l l Energy in light is contained in individual particles called photons l l Different colors have different energy l l No mass, just energy