Prepare your scantron: Use a pencil, not a pen! Fill in your name and fill the bubbles under your name. LAST NAME FIRST, First name second Put your 4-digit code instead of “IDENTIFICATION NUMBER”. --- (The last 4 digits of your OleMiss ID.) Question # 1: answer A Question # 2: answer C Question # 3: answer B Setup: Recall reading assignment: Chapter 5 (Light and matter): pp. 137 – 164 Please take a moment to mute your cell phone!

Photons Einstein’s  light comes in chunks (photons) discovery:  each photon has E=1240/l energy Red l = 720 nm, E = 1.7 eV Blue l = 420 nm, E = 3 eV UV l = 100 nm, E = 12 eV X-ray l = 1 nm, E = 1200 eV in electron-volts (eV) in nm’s Enough to destroy most atoms Destroys everything if strong

Phases The phases of matter  Solid  Liquid (only under pressure – rarely in astronomy)  Gas Phases Distinction looses sense under great pressure (inside stars or planets)  that matter is “mush” Hot matter: T > 1,000 - 2,000 K falls apart into atoms (gas or “mush”) T > 2,000 - 3,000 K atoms are ionized (plasma) Ultraviolet radiation will also ionize matter

Cosmic rays From Deep Space (??) The Solar Wind protons, electrons Earth’s atmosphere and magnetic field absorb them (dangerous for astronauts) very energetic protons & nuclei Break up into showers of many less energetic particles in the atmosphere. (always present: causes mutations)

Questions coming …

sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5 Question 4 What is ionization? A Molecules fall apart into atoms due to heat. Glowing gas is formed. B Nuclear processes in stars produce dangerous radiation. C Atomic nuclei fall apart into neutrons and protons. A neutron star results. D Atoms lose (some of) their electrons due to heat or UV radiation. The substance becomes plasma. Next question coming …

(Joseph von Fraunhofer, 1814) The device that resolves the colors of light: the spectroscope (Joseph von Fraunhofer, 1814) • Light from telescope enters slit (to block off stray light) • Prism (or grating) separates the colors • Produces spectrum on a screen/on a film (Put this device in a box and attach it to the telescope) The spectroscope Surprise: The spectrum of the Sun has black lines: Some colors are missing! (Fraunhofer-lines) Spectrum: each color is a “line”

The spectrum of the Sun Absorption lines (“Frauenhofer-lines”), (Color and b/w version of the same thing.) H H Absorption lines (“Frauenhofer-lines”), many in hydrogen wavelengths Here: colder gas takes out a few colors Solar atmosphere

the chemical composition Types of spectra Continuous spectrum (thermal glow & synchrotron radiation) Absorption spectrum (gas illuminated from behind) Emission spectrum (rarified gas: fluorescence) Each chemical element has its own spectral lines: A good way to tell the chemical composition of a star!

The spectra of stars – the effect of photospheric temperature

Questions coming …

sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5 Question 5 How do we know that the Sun is made mainly of hydrogen? A Its density equals the density of hydrogen. B Spaceships brought back a samples from the Sun. C Its spectrum contains hydrogen lines. D The gravity of the Sun can be explained only by hydrogen gas. E Only burning hydrogen (and no other gases) can produce enough heat to explain why the Sun is hot. Next question coming …

sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 6 Which one of the following types of spectra indicate the presence of cold gas located between a star and Earth? A Absorption spectra. B Emission spectra. C Continuous spectra. D Line spectra. E Band spectra.

sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 7 The spectrum of the Sun consists of A a few bright lines only. B dark lines over a bright continuum. C dark bands of light with bright centers, over a bright continuum. D a continuous bright spectrum like a rainbow. E a few bright bands with dark centers. Next question coming …