REMINDERS • Exam II next Thursday, April 14! • Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer • Review session (Q & A only) Tuesday, April 12 @ 7 pm Location: normal lecture hall in Physics REMINDERS • Exam II next Thursday, April 14! • Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer • Review session (Q & A only) Tuesday, April 12 @ 7 pm Location: normal lecture hall in Physics REMINDERS • Exam II next Thursday, April 14! • Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer • Review session (Q & A only) Tuesday, April 12 @ 7 pm Location: normal lecture hall in Physics Discussion REVIEW plan • 1 Chapters covered • 2 Main equations to know • 3 Brief overview & summary • 4 Sample discussion questions • 5 Sample multiple choice Material Covered • Chapter 5 – Light, interaction with matter, telescopes • Chapter 10 – The Sun • Chapter 11 – Stars – overview / properties • Chapter 12 – Stellar evolution • Chapter 13 – Deaths of stars • Textbook, lecture notes, discussion section activities! Important Relations L~M 3 E photon = hc / λ = h * frequency T ~ 1 / λ peak distance = 1 / parallax 4 2 4 2 L=4πr σ T ~ r T Brightness or Flux ~ 1 / (distance) 2 Key things to Memorize: • • • • • • • • Equations already mentioned EM spectrum HR diagram (most time on main sequence) Life cycle of a low & high mass stars Stellar Cutoffs – 8 M, 2 M, 1.4 M, 3 M Types of spectra & how they are formed Structure of our SUN What makes the sun shine? Evidence for nuclear fusion in the core. • H fusion – (4 H → 1 He + energy + neutrinos) • Spectral Sequence, luminosity class - OBAFGKM Key Concepts: • Longer wavelength photon → lower E • Shorter wavelength photon → higher E • Hydrostatic Equilibrium – Radiation pressure, degeneracy pressure (electron and neutron) vs. gravity • Doppler Effect • Distance determination – distance modulus, parallax Key Concepts (continued): • Bohr atomic model – explaining absorption/emission through electron transitions • Telescopes improve with collecting area and angular resolution • Positive nuclei repel, so high T required in stellar cores for fusion of heavier and heavier elements • Solar thermostat • Main sequence is a sequence of MASS Essay topics may include: • Describe the evolution of a low mass/high mass star • Draw and label an HR diagram • Emission/Absorption/Continuous spectra – Describe how each is produced • Newton’s form of Kepler’s 3rd law – calculating stellar masses • Binary star systems Essay topics may include: • Inverse square law (Flux vs. Luminosity) • Doppler shift • Describe Heliocentric Parallax and discuss the limits of this method • Why do we put telescopes into space? • Why does the sun shine? • What is the sun’s structure? Other stuff to emphasize: Know GENERAL idea ONLY: Concept Overview & Summary The electromagnetic spectrum Figure 3.5 Identify the following portions of the Electromagnetic spectrum: A B C D E The electromagnetic spectrum Figure 3.5 Which end of the spectrum is more energetic, A or B? Why? A B Gamma rays X-rays Ultraviolet Visible Infrared Microwaves Radio SHORT Wavelength ( λ ) LONG Wavelength ( λ ) HI Frequency ( ν or f ) LOW Frequency ( ν or f ) These two pictures describe what? “photon” & wave Light has a DUAL NATURE! “photon” & wave Energy of photon = (Planck’s constant) x (frequency) or (c / λ) If the Hydrogen gas cloud is moving towards Earth, the absorption line marked will shift in which direction? An absorption line of Hydrogen measured at rest A B How do light and matter interact? KNOW THESE DEFINITIONS! • • • • Emission Absorption Transmission Reflection or Scattering Electromagnetic radiation What does this diagram illustrate? Figure 3.8 What types of light spectra can we observe? 1. Continuous spectra 2. Absorption spectra 3. Emission spectra Which is the absorption spectra? Which is the continuous spectra? Which is the emission spectra? Which spectrum is coming from the coolest object? BLUE Yellow RED BLACK At what wavelength does the peak of the yellow spectrum lie? What type of star might this be? BLUE Yellow RED BLACK Is the star producing the yellow or red spectrum hotter? Why? BLUE Yellow RED BLACK Which spectrum is coming from the hottest object? BLUE Yellow RED BLACK Which star is more luminous? T = 15,000 K Radius = 1 unit T = 15,000 K Radius = 2 units Which star is more luminous? T = 3,000 K Radius = 1 unit T = 15,000 K Radius = 1 unit Which star is more luminous? T = 3,000 K Radius = 7 units T = 12,000 K Radius = 1 unit REMEMBER! Luminosity of a star is intrinsic. Depends on Temperature & Radius. L~R 2 4 T For which stars would we observe a Doppler Shift? A B C Doppler shift Figure 3.18 Doppler Effect Summary Motion toward or away from an observer causes a shift in the observed wavelength of light: • blueshift (shorter wavelength) motion _______ you • redshift (longer wavelength) motion AWAY from you • greater shift greater speed Doppler Effect Summary Motion toward or away from an observer causes a shift in the observed wavelength of light: • blueshift (shorter wavelength) motion toward you • redshift (longer wavelength) motion ______ from you • greater shift greater speed How do telescopes help us learn about the universe? • Telescopes collect more light than our eyes light-collecting area • Telescopes can see more detail than our eyes angular resolution • Telescopes/instruments can detect light that is invisible to our eyes (e.g., infrared, ultraviolet) Angular Resolution • The minimum angular separation that the telescope can distinguish. What is this diagram illustrating? Why can parallax only be used for nearby stars? Are the emission lines located in the UV part of the spectrum or the IR part of the spectrum? Which is the correct explanation for the sun’s shining? Is it on FIRE? Is it powered by NUCLEAR ENERGY? Is it CONTRACTING? E= ? mc - Einstein, 1905 In Einstein’s famous equation, what should the exponent be? This means that a ‘lil bit of mass can be converted to a LOT of energy The balance of the inward force of gravity with the outward force of pressure due to radiation is referred to as ? Solar wind A) Corona B) Chromosphere C) Photosphere D) Core Give the approximate Temperatures of each Of these layers. What enables nuclei to overcome repulsion and get close enough to fuse in the core of a star? ? Sun releases energy by fusing four hydrogen nuclei into what? IN 4 protons OUT 4He nucleus 2 positrons 2 gamma rays 2 _______???? What else results besides a He nucleus? Total mass is 0.7% lower Solar Thermostat Temperature Decreases Fusion Rate (Increases or Decreases)? Core (compresses or expands)? Temperature Restored How does the energy from fusion get out of the Sun? Why do sunspots appear dark on the surface of the sun? Number of sunspots rises and falls in cycle of ________ years. A difference between an ultraviolet photon and a radio photon is that • A. the energy of the radio photon is greater • B. only the radio photon is an electromagnetic wave • C. only the ultraviolet photon is an electromagnetic wave • D. the energy of the ultraviolet photon is greater • E. none of the answers are correct A difference between an ultraviolet photon and a radio photon is that • A. the energy of the radio photon is greater • B. only the radio photon is an electromagnetic wave • C. only the ultraviolet photon is an electromagnetic wave • D. the energy of the ultraviolet photon is greater • E. none of the answers are correct The speed of a radio wave is • • • • • A. B. C. D. E. the speed of sound slower than the speed of light slower than the speed of sound the speed of light none of the above The speed of a radio wave is • • • • • A. B. C. D. E. the speed of sound slower than the speed of light slower than the speed of sound the speed of light none of the above The sun • A. is composed of ionized gas that is mostly neon • B. is composed of molecular gas that is mostly neon • C. is composed of ionized gas that is mostly hydrogen • D. is composed of molecular gas that is mostly hydrogen The sun • A. is composed of ionized gas that is mostly neon • B. is composed of molecular gas that is mostly neon • C. is composed of ionized gas that is mostly hydrogen • D. is composed of molecular gas that is mostly hydrogen The energy source for the sun is • A. combustion of hydrocarbons • B. solar flares • C. nuclear fission, the splitting of two hydrogen atoms • D. nuclear fusion, the joining of two hydrogen atoms • E. combustion of hydrogen The energy source for the sun is • A. combustion of hydrocarbons • B. solar flares • C. nuclear fission, the splitting of two hydrogen atoms • D. nuclear fusion, the joining of two hydrogen atoms • E. combustion of hydrogen The layer of the sun that emits most of the light we see is • • • • A. the corona B. the chromosphere C. the photosphere D. none of the answers are correct The layer of the sun that emits most of the light we see is • • • • A. the corona B. the chromosphere C. the photosphere D. none of the answers are correct Electromagnetic radiation from astronomical objects can be studied from the surface of the Earth in which part of the spectrum? • A. gamma-rays • B. x-rays • C. radio Electromagnetic radiation from astronomical objects can be studied from the surface of the Earth in which part of the spectrum? • A. gamma-rays • B. x-rays • C. radio The hotter an object • A. the brighter it appears at all wavelengths, • B. • C. • D. • E. and the longer the wavelength at which it appears brightest the shorter the wavelength at which it appears brightest The brighter it appears at all wavelengths, and the shorter the wavelength at which it appears brightest the longer the wavelength at which it appears brightest the brighter it appears at all wavelengths The hotter an object • A. the brighter it appears at all wavelengths, • B. • C. • D. • E. and the longer the wavelength at which it appears brightest the shorter the wavelength at which it appears brightest The brighter it appears at all wavelengths, and the shorter the wavelength at which it appears brightest the longer the wavelength at which it appears brightest the brighter it appears at all wavelengths Heat affects wavelength Figure 3.6 An object emits an emission line spectrum. If the object moves towards an observer, • A. the observed emission lines shift to shorter wavelengths • B. the observed emission lines shift to longer wavelengths • C. the emission line spectrum shifts to a continuous spectrum • D. the emission line spectrum shifts to an absorption line spectrum An object emits an emission line spectrum. If the object moves towards an observer, • A. the observed emission lines shift to shorter wavelengths • B. the observed emission lines shift to longer wavelengths • C. the emission line spectrum shifts to a continuous spectrum • D. the emission line spectrum shifts to an absorption line spectrum The hottest part of the solar atmosphere • • • • A. B. C. D. found in sunspots is the photosphere is the corona is the chromosphere The hottest part of the solar atmosphere • • • • A. B. C. D. found in sunspots is the photosphere is the corona is the chromosphere Which of the following is ordered by increasing wavelength? • • • • A. B. C. D. infrared, visible, radio, gamma-ray visible, infrared, radio, gamma-ray gamma-ray, visible, infrared, radio radio, visible, infrared, gamma-ray Which of the following is ordered by increasing wavelength? • • • • A. B. C. D. infrared, visible, radio, gamma-ray visible, infrared, radio, gamma-ray gamma-ray, visible, infrared, radio radio, visible, infrared, gamma-ray An atom is ionized if • • • • A. B. C. D. it has lost a proton it has lost an electron it has lost a neutron it has absorbed a photon An atom is ionized if • • • • A. B. C. D. it has lost a proton it has lost an electron it has lost a neutron it has absorbed a photon Sunspots appear darker than the surrounding photosphere because • A. they have a carbonaceous composition • B. they have an icy composition • C. they are cooler than their surroundings • D. they are shadowed from coronal radiation Sunspots appear darker than the surrounding photosphere because • A. they have a carbonaceous composition • B. they have an icy composition • C. they are cooler than their surroundings • D. they are shadowed from coronal radiation High mass stars have shorter lifetimes than low mass stars because high mass stars • A. have luminosities that are far larger than low mass stars • B. have less hydrogen than low mass stars • C. have less helium than low mass stars • D. release less energy per nuclear reaction than low mass stars High mass stars have shorter lifetimes than low mass stars because high mass stars • A. have luminosities that are far larger than low mass stars • B. have less hydrogen than low mass stars • C. have less helium than low mass stars • D. release less energy per nuclear reaction than low mass stars If the Sun were replaced by a black hole of the same mass, • A. a great sucking sound would be heard • B. the Earth would continue to orbit pretty much as it does now • C. the Earth would fall directly towards the black hole • D. the Earth would spiral into the black hole over the next 1000 years If the Sun were replaced by a black hole of the same mass, • A. a great sucking sound would be heard • B. the Earth would continue to orbit pretty much as it does now • C. the Earth would fall directly towards the black hole • D. the Earth would spiral into the black hole over the next 1000 years The most common stars are • • • • • A. B. C. D. E. lower main sequence stars supergiants giants upper main sequence stars neutron stars The most common stars are • • • • • A. B. C. D. E. lower main sequence stars supergiants giants upper main sequence stars neutron stars Main sequence stars • A. are stars which have no hydrogen or helium • B. have nuclear fusion of hydrogen occurring in their cores • C. are stars which are mostly made of hydrogen • D. are stars found in spiral arms Main sequence stars • A. are stars which have no hydrogen or helium • B. have nuclear fusion of hydrogen occurring in their cores • C. are stars which are mostly made of hydrogen • D. are stars found in spiral arms A planetary nebula is • A. produced by a supernova explosion • B. a nebula within which planets are forming • C. the expelled outer envelope of a medium mass star • D. a cloud of hot gas surrounding a planet A planetary nebula is • A. produced by a supernova explosion • B. a nebula within which planets are forming • C. the expelled outer envelope of a medium mass star • D. a cloud of hot gas surrounding a planet The density of a __________ is greater than the density of a ___________. • • • • • A. B. C. D. E. neutron star, black hole pulsar, neutron star pulsar, white dwarf white dwarf, pulsar white dwarf, black hole The density of a __________ is greater than the density of a ___________. • • • • • A. B. C. D. E. neutron star, black hole pulsar, neutron star pulsar, white dwarf white dwarf, pulsar white dwarf, black hole