1. Astronomy 1020-H Stellar Astronomy Spring_2016 Day-12

3. Course Announcements 1 st Quarter observing night: TONIGHT @ 7:30pm READ through the “Format for the Report” BEFORE you come. N5 Mean73.3 Std. Dev.14.2 Median79.2 Mode--- Min.56 Max.87.2 Curve---

4. The Origin and Nature of Light

5. Lab This Week The Spectrometer What you need to know: You get to visualize the spectra from various sources. Reading ahead in Chapter 5 will help.

6. Lab This Week The Spectrometer

7.  Almost all knowledge of the universe beyond Earth comes from light.  Light can tell us about objects in space: temperature, composition, speeds, and more.

8. What Light Can Tell Us. Photometry – Study of Brightness: Luminosity, Est. of Distance, Rough Temp. of Star Spectroscopy – Study of the EM Spectrum: Composition, Radial Velocity, Temp., Surface-gravity Mass for compact objects Astrometry – Study of Positions: Tangential Motion, Distance Polarimetry – Study of Polarization of Light: Magnetic Field

9. Spectrum of the Sun

11. But, what is light? Newton, Remember Newton? He did more than just calculus and mechanics. In the 17th Century, Isaac Newton argued that light was composed of little particles while Christian Huygens suggested that light travels in the form of waves. In the 19 th and 20 th Century Maxwell, Young, Einstein and others were able to show that Light behaves both like a particle and a wave depending on how you observe it.

12. Particle Nature

13. Thomas Young’s interference experiment Wave Nature

14. Accelerating charges (think electrons and protons) produce light – electromagnetic radiation! But, where does light actually come from?

15. Photons  Light also behaves as a particle.  Photon: particle of light.  Photons carry energy and can have different amounts of energy.  Photons with high energy = light with high frequency.  Photons with low energy = light with low frequency.  Atoms can absorb or emit photons.

16. Einstein (Nobel Prize) In 1905 Einstein calculated the energy of a particle of light (photon) and proposed the photoelectric effect. E photon = hc/  = h e- photon

17.  Light moves at 300,000 km/s in a vacuum.  First measured by Rømer when observing Jupiter’s moons.  Speed is slower in other materials, e.g., glass.

18.  Wavelength ( ): length between crests.  Amplitude: height.  Frequency (f): number of waves that pass by each second.  Period (P): time to complete one cycle.

19.  A long wavelength means low frequency.  A short wavelength means high frequency.  The speed of light, c, is constant.

20.  Light is a wave of combined electricity and magnetism, called an electromagnetic wave.  Changing electric and magnetic fields create a self-sustaining electromagnetic wave.

21. Maxwell – EM Field Theory Scottish physicist James Clerk Maxwell showed mathematically in the 1860s that light must be a combination of electric and magnetic fields.

22.  Knowing the speed of light and one other variable, either the wavelength or frequency of the light in question, you can find the remaining quantity.  Example: Find the wavelength of the light wave coming from a radio station broadcasting on 770 AM: MATH TOOLS 5.1

23. Like the flavors of Ice cream – they each provide us with different information. EM Spectrum But what do you get when you put all the flavors (light) together?