1. ASTR-1010 Planetary Astronomy Day - 16

2. Announcements Homework Chapter 3: Due Wednesday Feb. 24 Smartworks Chapters 4 & 5 are also posted Exam 2 will cover chapters 3, 4, & 5 Ranking Task (Gravity) due now. 1 st quarter observing night: Wednesday!!

3. Photograph of a Star Cluster

4. Spectra of a Star Cluster

5. ClassAction Stuff Hydrogen atom simulator Splash page warm up

6. 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.

7. Thomas Young’s interference experiment

8. Scottish physicist James Clerk Maxwell showed mathematically in the 1860s that light must be a combination of electric and magnetic fields.

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

10. But, where does light actually come from? Light comes from the acceleration of charged particles (such as electrons and protons)

11. electron Accelerating charges produce light – electromagnetic radiation! But, where does light actually come from?

12. The Electro-Magnetic (EM) Spectrum The EM spectrum covers the entire range of wavelengths. All waves travel at one speed (c, the speed of light).

13. Tutorial:– p.45 EM Spectrum of Light Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. Work with a partner! 5 minutes

14. An atom consists of a small, dense nucleus (containing protons and neutrons) surrounded by electrons - Model Proposed by Niels Bohr 1913

15. A nucleus is about 10 -15 m in size and the first electron orbits out at 10 -10 m from the center of the atom – The size of the electron orbit is 100,000 times greater than the size of the nucleus Atoms are mostly empty space

16. So if a nucleus the size of an orange (10 cm) was located at the center of the football field, where would the electron be? End Zone? Grandstands? On Campus? In Clarksville?

17. If the electron’s orbit is 100,000 times bigger than the nucleus then the electron would be 10,000 m or 6.21 miles away from the center of the Football Field! Still in Clarksville, but near exit 11.

18. The electron should be thought of as a distribution or cloud of probability around the nucleus that on- average behave like a point particle on a fixed circular path

19. Nucleus

20. Photons (light-waves) are emitted from an atom when an electron moves from a higher energy level to a lower energy level Nucleus

21. Photons (light-waves) can also be absorbed by an atom when an electron moves from a lower energy level to a higher energy level Nucleus

23. ClassAction Stuff Hydrogen atom simulator

24. Tutorial:– p.63 Light & Atoms Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. Work with a partner! 15 minutes