4 th & 5 th lectures; Mon & Tues, July 7 & 8Crib notes 7/6/20087/6/2008. Sun and processes

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1 4 th & 5 th lectures; Mon & Tues, July 7 & 8Crib notes 7/6/20087/6/2008 Topics Sun and processes Chart of spectrum and features has been uploaded To blackboard and web Ask how many students have accessed the blackboard? Announce that this week, try to get through Ch20. I will tell them on Tuesday what chapters they will be responsible for on Thursday s exam. (given 2 nd half of class) Chapter 17 nature of stars Use mainly Evans Ch 11 Notes and Keywords source of continuous spectrum produces an absorption line spectrum. Sunspot cycle # 35 Sunspot number is no. of spots plus 10 time number of groups. Iclicker Ch 16 starts with equilibrium; then nuclear reactions; neutrinos vs electrons; convection, # 12 newch16: # 25 temperature of corona high temperature of corona; light is mostly in the ultraviolet, and in X rays Coronal holes are believed to be the source of the solar wind Electron, nuclei of hydrogen, helium and some heavier elements Need to show magnetic fields, # 38 coronal loops, CME # 42. space weather, effect of sun on earth Starts with parallax; use Evans Ch11 Some good animations Inverse square law relating apparent brightness and luminosity See Iclicker 17 # 8 Luminosity, L = 4 * pi * d 2 * brightness Apparent magnitude vs absolute magnitude m 2 m 1 = 2.5 log(b 1 / b 2 ) See iclicker Ch17 #10 Classification, OBAFGKMLT; emphasize based on temperature of photosphere Women at Harvard College Observatory, late 19 th century Binary stars ECP_3 Ch11 #30; Go through # 40, then change to Ch17 Go to Ch 17 nature of stars # 24, 25, 26 Hertzsprung Russell diagram Mass luminosity relations L ~ M 3.5

2 Chapter 18 birth of stars Syllabus says Monday, July 7; lecture # 4 Emission nebulae Reflection Nebulae Dark nebulae (Barnard Objects) Chapters 18 & 19 deal with stars from their birth to their death. Syllabus: Tues, July 8, review and catchup, Can spend more time on L/T pp (H R diagrams) Need to tell them what chapters will be on Thursday s exam Ch 19 Stellar evolution on and after the main sequence Syllabus says Wed, July 9 Radius of stars; use L = 4* π R 2 *σ*t 4 Betelguese is 60,000 more luminous than the sun & has a surface temperature of 3,500 K, what is its radius. Sun s radius is 6.96* 10 5 km; get B s radius is 4.7* 10 8 km (Mars distance is 2,28* 10 8 km # 41 is H R diagram showing RED Giants Emphasize that Main Sequence are hydrogen burning stars H R are in L/T pp Iclicker Ch 17 Main sequence questions; ECP3_11 # 60 to 72 Mainly, this chapter deals with birth of stars through contraction from large molecular clouds Birth of stars Ch18 Star clusters # 16 Types of nebulae Emission nebula emit their own light, near O and B stars Also called H II ionized hydrogen atoms, light is formed from recombination Protostars form in cold, dark nebulae Called Barnard objects except small spherical dark nebulae are called Bok globules Iclicker 18 Evolution of stars after exhaustion of their core hydrogen. A star s lifetime is proportional to its mass cubed; Lifetime ~ M 2.5 Note that luminosity L ~ M 3.5 When core hydrogen is consumed, the star starts to burn helium in its core,

3 Stellar Evolution and the Death of stars This is chapter 20 of text Do Thursday before exam Note that this is treated in Ch22a of viewgraphs and hydrogen in an expanding shell. Stellar evolution depends very critically on the mass of the star. Ch19 # 15 shows H R diagram for sun over time # 17,18,19, etc. evolution of stars in star clusters Go to ECP3_11, # 53 with more massive stars exhausting their hydrogen much more quickly. Then go to pulsating stars, Cepheid variables Binaries, Roche lobe, mass transfer. Iclicker ch 19 Note that =.064 Goes to helium burning, horizontal branch Ch22a viewgraphs Good viewgraph # 7 AGB branch Degeneracy, ECP12 # 30 White dwarfs Ch22a # 18 Supernovae process; Start with # 21 Also Type 1a supernovae, # 32 Iclicker # 20

4 1. The Sun's source of energy at the present time is thought to be A) thermonuclear fusion (combining) of hydrogen atoms. B) thermonuclear fission (splitting) of heavy elements into hydrogen. C) chemical burning of hydrogen gas with oxygen. D) gravitational contraction. Nuclear fusion is A) the combining of electrons with nuclei to produce atoms and release energy. B) the combining of hydrogen atoms to produce hydrogen molecules, H 2, and energy. C) the process of fusing together light nuclei (e.g., hydrogen) to produce heavier nuclei (e.g., helium) and energy. D) the splitting of heavier nuclei to produce lighter nuclei and energy. Hydrogen "burning" by fusion reactions occurs only in the deep interior of the Sun (and other stars), because this is the only place in the Sun where A) there is sufficient hydrogen. B) the density is sufficiently low for the high temperature atoms to build up enough energy to collide and undergo fusion. C) the temperature is low enough and the density is high enough to allow hydrogen atoms to collide with each other often enough for fusion to occur. D) the requisite conditions of high temperature and high density occur. How much longer can the Sun continue to generate energy by nuclear reactions in its core? A) about 500,000 years C) about 5 billion years B) about 50 billion years D) about 5 million years The phrase "hydrostatic equilibrium" in the Sun refers to A) the balance of gas pressure outward and magnetic forces inward. B) the creation of one helium nucleus for the "destruction" of every four hydrogen nuclei. C) the balance of gas pressure inward and heat outward. D) the balance of gravity inward and gas pressure outward. The neutrino is A) a tiny particle that interacts very weakly with matter, with extremely low or zero mass and no charge. B) another name for the neutron, a component of almost all atomic nuclei, with a mass close to the proton and no charge. C) another name for a photon of very high energy, i.e., short wavelength electromagnetic radiation, with great penetrating power. D) a massive but very elusive nuclear particle that carries most of the energy generated in the core of the Sun to the surface, but that then decays to release electromagnetic radiation (i.e., light).

5 What is the photosphere of the Sun? A) the core of the Sun, where nuclear energy is generated B) the region of convecting gases below the visible surface of the Sun C) the middle layer of the Sun's atmosphere D) the visible "surface" of the Sun If granulation on the Sun's surface is a result of convective motion below it, and material is upwelling at the centers of granular cells and returning in the regions between cells, what is the expected temperature distribution across a granular cell? A) The center of a cell will be cooler than the edges. B) Alternate cell centers will be hot and cold, with the edges at an intermediate temperature. C) Temperature will be uniform across the cell. D) The center of a cell will be hotter than the edges. The appearance of the visible spectrum of the Sun, when its light is separated in its component colors, is A) a uniform continuous spectrum with no structure. B) a spectrum containing many dark absorption and many bright emission lines on a continuous background. C) a continuous bright spectrum, crossed by thousands of dark absorption lines. D) a spectrum consisting only of a few bright emission lines. The approximate temperature of the visible surface of the Sun is In order from lowest to highest, what are the names of the three layers in the Sun's atmosphere? A. photosphere, chromosphere, corona B. corona, chromosphere, photosphere C. photosphere, corona, chromosphere D. chromosphere, corona, photosphere Where is the chromosphere on the Sun? A) It is the visible surface of the Sun. B) It is the layer above the visible surface of the Sun. C) It is the outermost part of the Sun's atmosphere. D) It is the layer below the visible surface of the Sun.

6 The corona of the Sun has a temperature A) of about 10 K, because it merges with cold interstellar space. B) about the same as the photosphere about 6000 K. C) noticeably less than the photosphere about 1000 to 2000 K. D) of 1 to 2 million K. Observations of the spectrum of the solar corona reveal emission lines that come from atoms from which many electrons have been stripped. What conclusion can be drawn from this result? A) The solar rotation speed at coronal height reduces the ability of atoms to retain electrons. B) The pressure of the gas is sufficient to squeeze the electrons from the atoms. C) The magnetic field intensity is high enough to drag electrons from the atoms. D) The atomic collision energies and hence the gas temperatures are extremely high. What is the source of the X rays emitted by the solar corona? A) radioactivity in the coronal gases B) X rays from the solar photosphere scattered from ions in the corona C) the high temperature gas of the corona D) high-energy charged particles spiraling along the coronal magnetic fields What is the solar wind? A) the storm of waves and vortices on the Sun's surface generated by a solar flare B) the constant flux of photons from the Sun's visible surface C) the circulation of gases between the equator and the poles of the Sun D) the Sun's outer atmosphere streaming out into space What is the source of the solar wind? A) gas flung out from solar flares B) gas escaping from X-ray-bright regions of the solar corona C) gas flung out from the Sun's equatorial region by the centrifugal force due to the Sun's rotation D) gas escaping through coronal holes The rotation of the Sun is A) fastest at the equator, slowest at mid-latitudes, rising to intermediate speeds near the poles. B) fastest at mid-latitudes, slower at the equator, and slowest near the poles. C) fastest at the equator, slower at mid-latitudes, and slowest near the poles. D) slowest at the equator, faster at mid-latitudes, and fastest near the poles.

7 What is the average length of time from one maximum in the number of sunspots on the Sun to the next maximum? A) about 2 months B) 7 years C) 11 years D) 22 years Sunspots are cooler than the rest of the Sun's surface, sometimes by as much as 1500 K. What would be the peak wavelength of the radiation from the sunspot, when compared to that from the rest of the Sun? A) It would be at a shorter wavelength. B) It would be at a longer wavelength. C) It could be at a shorter or longer wavelength, depending on the position of the spot. D) It would be the same, because the light still originates from the hydrogen gas of the Sun. What is the name of a large loop of bright gas extending outward from the edge of the Sun (often seen during total solar eclipses)? What name is given to a dark line or streak often seen in hydrogen light photographs of the solar chromosphere, and often observed in association with sunspots? Solar flares, the violent eruptive events on the Sun, occur most frequently A. over single, isolated, but large sunspots. B. in or above complex sunspot groups. C. within solar coronal holes, from which the solar wind originates. D. along the solar equator at positions aligned with Jupiter's position, caused by tidal disturbance on the Sun. What are the most energetic eruptive events to occur on the Sun? A) thermonuclear explosions C) coronal mass ejections B) erupting prominences D) solar flares

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