Intro to Galaxies Light and Atoms - I

Transcription

1 Astrophysics Study of Light Study of Atoms Intro to Galaxies Light and Atoms - I 1

2 Atomic Physics elements: substances which cannot be broken down into simpler substances atom : smallest unit of an element that displays the chemical properties of the element compounds: substances made up of two or more elements molecule: smallest unit of a compound that still has the chemical properties of the compound Intro to Galaxies Light and Atoms - I 2

3 Model of an Atom rapidly moving electron (low mass) dense nucleus of neutrons and protons (massive particles) proton: positively charged electron: negatively charged neutron: no charge Intro to Galaxies Light and Atoms - I 3

4 Hydrogen Atom most common element in the Universe! nucleus, size of a marble electron is 1 km away e - p + Intro to Galaxies Light and Atoms - I 4

5 Number of protons in an atom is what makes one element different from another Hydrogen - 1 protons Helium - 2 protons Carbon - 6 protons Electrons determine the chemical properties of atoms. Intro to Galaxies Light and Atoms - I 5

6 neutral atoms: electrons = protons isotopes: same element with different number of neutrons ions: electrons = protons e.g. an atom loses an electron - positively charged - called a positive ion Intro to Galaxies Light and Atoms - I 6

7 Light spectroscopy: art of breaking up light into its component colors spectrum: sequence of colors resulting from dispersing light through a prism, a grating or a raindrop R O Y G. B I V Intro to Galaxies Light and Atoms - I 7

8 continuous spectrum: broad bands of color with no breaks, no separations line spectrum: a bright sharp line (or lines) in a particular color a dark line where light is missing in a particular color Intro to Galaxies Light and Atoms - I 8

9 emission spectrum: bright line spectrum absorption spectrum: continuous spectrum with superimposed dark lines spectroscope: an instrument for observing details in a spectrum Intro to Galaxies Light and Atoms - I 9

10 Experiments neon sign bright emission lines in red mercury street light bright emission lines in yellow & green sodium street light bright emission lines in yellow salt in a colorless flame series of bright emission lines, a pair in yellow Intro to Galaxies Light and Atoms - I 10

11 Each chemical element displays a unique arrangement of bright lines when excited (i.e. heated) in a gaseous state. Intro to Galaxies Light and Atoms - I 11

12 Look at sunlight (not directly, but reflected) We see dark lines imposed on a continuous spectrum, specifically a pair in the yellow part of the spectrum. A match for the pair of bright yellow lines seen in a sodium flame! This tells us there is sodium present in the Sun! Intro to Galaxies Light and Atoms - I 12

13 Spectrum of the Sun Kaufmann & Comins 4/e Intro to Galaxies Light and Atoms - I 13

14 Zeilik 6/e Spectrum of the Sun Intro to Galaxies Light and Atoms - I 14

15 Solar Spectrum Zeilik 6/e Intro to Galaxies Light and Atoms - I 15

16 Spectrum of Star, Canopus Zeilik 6/e Intro to Galaxies Light and Atoms - I 16

17 Kirchhoff s Rules Rule #1: A hot opaque solid, liquid or highly compressed gas, emits a continuous spectrum. Kaufmann & Comin 4/e Intro to Galaxies Light and Atoms - I 17

18 Rule #2: Kaufmann & Comin 4/e A hot, transparent gas produces a spectrum of bright lines emission lines). The number and color of the lines depend on which elements are in the gas. Intro to Galaxies Light and Atoms - I 18

19 Rule #3: Kaufmann & Comin 4/e If a continuous spectrum (from a hot, opaque solid, liquid or gas) passes through a transparent (i.e. cooler) gas, the cooler gas causes the appearance of dark lines (absorption lines) in the continuous spectrum. The number of color of lines depend on which elements are present in the cooler gas. Intro to Galaxies Light and Atoms - I 19

20 Kaufmann & Comin 4/e Intro to Galaxies Light and Atoms - I 20

21 Energy energy: ability to do work conservation of energy: total energy of an isolated system remains constant regardless of what changes happen inside the system Intro to Galaxies Light and Atoms - I 21

22 kinetic energy: energy of motion KE = 1/2 m v 2 depends on mass and velocity potential energy: energy that is stored due to an applied force - potential to do work - fuels, batteries gravitational potential energy: energy of position radiative energy: energy carried by light Intro to Galaxies Light and Atoms - I 22

23 Conservation of Energy Energy cannot be created or destroyed; it may be transformed but the total does not change. Intro to Galaxies Light and Atoms - I 23

24 Light and Electromagnetic Radiation waves: undulations with a regular timing Intro to Galaxies Light and Atoms - I 24

25 frequency: number of waves per second wavelength: distance from one peak to another peak wavelength Intro to Galaxies Light and Atoms - I 25

26 velocity: how fast the wave is traveling and in what direction No matter moves with waves; wave carries energy but does not transport materials. Intro to Galaxies Light and Atoms - I 26

27 Fundamental Rule for Light f l = v f = frequency l = wavelength v = velocity The speed of light is called, c for light the rule is: f l = c c = 300,000 km/sec Intro to Galaxies Light and Atoms - I 27

28 f l = c Given that the speed of light is constant: change in frequency change in wavelength increase the frequency, wavelength decreases????? decrease the frequency, wavelength increases????? an inverse relationship Intro to Galaxies Light and Atoms - I 28

29 Electromagnetic Spectrum complete range of wavelengths of EM radiation gamma rays x-rays ultraviolet rays (UV) visible infrared (IR) microwave radio waves Intro to Galaxies Light and Atoms - I 29

30 The ElectroMagnetic Spectrum Kaufmann & Comin 4/e Intro to Galaxies Light and Atoms - I 30

31 Kaufmann & Comin 4/e Intro to Galaxies Light and Atoms - I 31

32 Ground-based vs Hubble Light Pollution Tucson 1959 vs 1980 Kaufmann & Comin 4/e Intro to Galaxies Light and Atoms - I 32

33 APOD USA at Night from Space Intro to Galaxies Light and Atoms - I 33

34 angstrom:, unit of measure for wavelength 1 = m hertz: unit of measure for frequency, number of cycles per second visible light - red 7000 violet 4000 Intro to Galaxies Light and Atoms - I 34

35 Why the pattern of light and dark lines?... stay tuned Intro to Galaxies Light and Atoms - I 35