Stars: Intro & Classification Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Quotes & Cartoon of the Day “The wonder is, not that the field of stars of so vast, but that man has measured it.” — Anatole France, The Garden of Epicurus, 189 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Announcements • SS Homework posted, due 11/19 • Midterm — will debrief THURSDAY • Anybody see the…. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Last Class • Solar System Topics Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 This Class • Intro to Stars • Temperature, Color & Size • Stellar Classification • Intro to the HR Diagram • LT HR Diagram Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Stars, Temperature and Color Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Recall What a Star Is • A sphere of hot gas • mostly hydrogen & helium • Interior hot enough to undergo nuclear fusion • most commonly H —> He • above 107 K = 10 million K (18 million °F) • Held together by gravity Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Fundamental Properties of Stars • TEMPERATURE • color, spectral properties • LUMINOSITY • inherent brightness • amount of energy generated in the star and released as electromagnetic radiation • SIZE • Radius & Mass • DISTANCE • CHEMICAL COMPOSITION Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Luminosity • Luminosity is a measure of the rate at which a star puts out energy. • Larger luminosity — appears brighter • measured in J/s or “watts” • sometimes relative to the Sun, in “solar luminosities” L☉ • L stands for luminosity, ☉ stands for Sun • The Sun has a luminosity of 3.846×1026 W Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 HOW HOT IS THAT STAR? Recall: Why Stars Shine • Visible Sun is a hot layer of gas • about 5800 K (5525°C, 9980°F) • not as hot as the center! • Glows due to hot material • Other stars have similar structure, range of surface temperature Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Blackbody Radiation • white light spectrum is continuous • no gaps between colors • the hotter you heat something, the bluer it appears • Thermal (heat related) radiation from (relatively) hot bulk matter • This is called blackbody radiation Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Light diagnoses Temperature Colder feeling warm faint reddish glow brighter red glow bright orange very bright yellow extremely bright white http://i302.photobucket.com/albums/nn114/fiddlegirl89_photos/Dave/DSC00596-1.jpg bluish white Warmer Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Spectrum of the Sun • Stars emit light as blackbodies to a large extent. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Shape of Blackbody Spectrum Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Temperatue affects Color & Luminosity • Hotter = greater luminosity • appears brighter • peak of curve higher • technically greater luminosity per unit surface area • Hotter = bluer • peak of curve more to left • more blue mixed in with red light Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice A lump of lead is heated to a high temperature. Another lump of lead that is twice as large is heated to a lower temperature. Which lump of material appears bluer? A. The cooler lump appears bluer B. The hotter lump appears bluer C. Both lumps appear the same color D. Cannot tell which lump appears bluer Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 When something is “red hot”, it is hotter than something that is A. blue hot B. white hot C. neither of these D. both of these Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 SIZE, COLOR AND TEMPERATURE Recall http://www.skinnerscience.com/Year %2012,13/astrop3.jpg • Hotter -> Brighter • Hotter -> Bluer • Bigger is also brighter! • a star with a larger diameter has a greater luminosity Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Analogy • LED spotlight w/60 LEDs • Total output ~1000 lumens • comparable to 100-watt bulb • each LED 1/60 of 1000 lumens • ~16.7 lumens • surface T gives you “per-LED” luminosity not total for star Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Stephan-Boltzman Law is brighter than is brighter than is brighter than could be brighter than could be brighter than Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice Star Yoda is a small blue star and star Chewbacca is a large red star. Which is brighter? (in terms of light output, not intelligence...) A. Yoda B. Chewbacca C. They have the same brightness. D. It’s not possible to tell. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 70 Blackbody Radiation – Instructor’s Guide 2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B? a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above. 3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B c) Both stars peak emissions are at the same wavelength. d) None of the above are possible. 4) Use the graph at right to determine which of the two stars (A or D) gives off more green light? a) Star A b) Star D c) They both give off the same amount of green light. Use the graph at right to determine which of the two stars (A or C) has a higher luminosity? 5) Use the graph at right to determine which of the two stars (A or C) is at a higher temperature? a) Star A b) Star C c) The two stars have the same temperature. d) It is not possible to determine this. 6) Use the graph at right to determine how the size of Star A compares to the size of Star C. a) Star A is smaller than StarA. C.Star A b) Star A is larger than Star C. c) The stars are the same size.B. Star C d) It is not possible to determine this. C. The two stars have the same luminosity. D. It is not possible to determine this. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 © 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy Third Edition Use the graph at right to determine which of the 70 following bestBlackbody describes Radiation how Star – In Astructor’s would appear Guide as compared with Star B? 2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B? a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above. 3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B A. Star A would appear more red than Star B. c) Both stars peak emissions are at the same wavelength. d) None of the aboveB. areBoth possible. stars would appear the same color. C. Star A would appear more blue than Star B. 4) Use the graph at right to determine which of the two stars (A or D) gives off more green light? a) Star A Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 b) Star D c) They both give off the same amount of green light. 5) Use the graph at right to determine which of the two stars (A or C) is at a higher temperature? a) Star A b) Star C c) The two stars have the same temperature. d) It is not possible to determine this. 6) Use the graph at right to determine how the size of Star A compares to the size of Star C. a) Star A is smaller than Star C. b) Star A is larger than Star C. c) The stars are the same size. d) It is not possible to determine this. © 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy Third Edition Use the graph at right to determine which of the two 70 stars (A or BBlackbody) is at a higher Radiation temperature? – Instructor’s Guide 2) Use the graph at right to determine which of the following best describes how Star A would appear as compared with Star B? a) Star A would appear more red than Star B. b) Both stars would appear more red than blue. c) Both stars would appear more blue than red. d) Star A would appear more blue than Star B. e) None of the above. 3) Use the graph at right to determine which of the two stars (A or B) emits light with the longer peak wavelength? a) Star A b) Star B A. Star A is at a higher temperature than Star B. c) Both stars peak emissions are at the same wavelength. d) None of the aboveB. areBoth possible. stars have the same temperature. C. Star B is at a higher temperature than Star A. 4) Use the graph at right to determine which of the two stars (A or D) gives off more green light? a) Star A Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 b) Star D c) They both give off the same amount of green light.