Visions of the Universe
Visions of the Universe ISP 205
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Visions of the Universe Final Exam Review Chapter 1 Earth 150 million km from the sun Milky Way galaxy has 100 billion stars and is 100000 light years in diameter Universe 0 Milky Way Galaxy is one of 100 billion galaxies o 1022 stars Observable Universe 14 billion light years Cosmic history All of recorded human history 30 seconds 1 month 12 billion years Almost everything in the universe rotates and orbits counter clockwise Solar System is 28000 light years from center of galaxy Galaxies move with the expansion of the universe 0 Almost all galaxies appear to be moving away from us 0 The farther away they are the faster they are moving away 0 Every point is receding from every other point no center poin Measuring the rate of expansion of the universe gives the age of the universe Chapter 2 Constellation region of the sky The stars appear to lie on a celestial sphere even though they are really at different distances The Celestial Sphere is divided into 88 Constellations The Milky Way in our night sky is actually our view into the disk of the milky way galaxy North Celestial Pole 9 above north pole Celestial equator 9 above equator South Celestial Pole 9 above south pole Objects position in sky is given by altitude and direction Latitude position north or south of equator Longitude position east or west of prime meridian Circumpolar stars never set Stars and everything rise in the east and set in the west Earth is closest to sun in January Earths orbit is nearly circular ellipse distance not cause of seasons Solstice Time when difference between directness of sunlight between north and south is greatest Equinox Time when directness of sunlight in north and south are equal Winter Solstice December 21 Spring Equinox April 21 Summer Solstice June 21 Fall Equinox September 21 Season changes are more extreme at high latitudes Precession causes Earth s rotation axis to trace a circle in space over the course of about 26000 years because of this Earth s position in orbit on a particular date slowly shifts El Gordo cluster of galaxies We see different phases of the moon because our View of the side of the moon lit by the sun changes as the moon orbits earth goes through one cycle of phases about 295 days 1 month Moon Phases 0 New 0 Waxing Crescent 0 First Quarter 0 Waxing Gibbous 0 Full 0 Waning Gibbous 0 Third Quarter 0 Waning Crescent How to solve moon problem 1 Locate the sun earth moon as viewed from above the north pole 2 Which way does the earth turn 3 Locate yourself for the appropriate action and gure what time it is What causes eclipses A solar eclipse happens when the moon block our view of the sun Solar Eclipse Moon shadow on Earth Lunar Eclipse Earth s shadow on Moon Moons angular size in sky is almost identical to Sun s angular size a cause of eclipse Eclipses occur when moon is new or full near the nodes Umbra the sun is completely block Penumbra partial solar eclipse Annual Solar eclipse can occur when the moon is too far for the umbra to reach earth Totality when complete solar eclipse occurs Apparent Retrograde Motion planet will appear to drift from east to west on the celestial sphere occurs when Earth s orbit carries it past another planet Parallax apparent shift in position of a nearby object as our point of view changes Chapter 3 Ancient Accomplishments o Timekeeping and standards 0 Navigation 0 Predicting Season 0 Predicting Eclipses Our mathematical and scientific heritage originated with the civilizations of the Middle East Greeks first to make models of nature Greeks thought of geocentric universe Eratosthenes accurately measured earth Ptolemy Geocentric Model used 1500 years Copernicus proposed in 1543 that the sun not the earth was of the center of the solar system Tycho Brahe best nakedeye observer Kepler used Tycho data for elliptical orbits Keplers 3 Laws of Planetary Motion 1 Every orbit is an ellipse where the sun is at a foci 2 When a planet is close moves faster when far away moves slowly but sweeps out equal area in equal time 3 P2 a3 the more distant the planet the slower average speed Galileo using his telescope proved moon was not a perfect sphere also saw 4 moons orbiting Jupiter proving everything doesn t orbit earth saw Venus goes through phases proving it orbits sun not earth Science vs Non Science 0 Scienti c Method 0 Observations o Sorting and classifying and then identify patterns Hallmarks of Science 1 Modern Science seeks explanations for observed phenomena that rely solely on natural causes 2 Science progresses through the creation and testing of models of nature that explain the observations as simply as possible 3 Modern science makes testable prediction scienti c results can be repeated reproduced and veri ed Scienti c Theory supported by a large compelling body of evidence and must be falsi able Chapter 4 Speed distance in a given time Velocity speed and direction Acceleration change in velocity in a given time Gravity 98 ms392 Momentum mass X velocity the only way to change an objects momentum is to apply a force Mass total amount of matter Weight the force that gravity puts on an object Newtons Three Law 1 Object moves at constant velocity unless a force acts upon it 2 F ma 3 For any force there is an equal and opposite force Conservation of Momentum o In any interaction the total amount of momentum doesn t change 0 Forces merely transfer momentum from one object to another Gravity constantly exerts forces between planets and sun keep the planets in orbit Angular momentum mass X velocity X radius Conservation of Angular Momentum o In any interaction of total amount of angular momentum does not change 0 As radius decreases spin velocity increases Kinetic Energy energy of motion Potential Energy stored energy Radiative Energy energy of light Temperature Kelvins temperature unit T in kelvin is directly proportional to the random Kinetic Energy of the gas particles 273K0degC0K273 C0 The force of gravity between two objects depends on the product of their masses and the square of the distance between them Flg G X M1M2d2 Escape Velocity specifies the speed needed to escape an objects surface The shape of an orbit depends on the total amount of energy Kepelers Third Law is how we measure a mass P21M1M2 x213 Planets weigh much less than stars Planets mass is too tiny to change its orbit Chapter 5 A spectrum is a plot of light intensity vs wavelength 1 Light as a wave 9quot DP0 Wavelength distance between peaks Frequency the number of times per second the wave bops up and down l Hertz 1 cycle per second Light interacts with magnetic and electric charges C 300000 kmsec speed of light Wavelength X Frequency C Remember order of Electromagnetic Spectrum 2 Light as a particle a b Photons particles of light The higher the frequency higher the energy Elements and Atomic Structure 0 Elements are made of atoms 0 Atom charge O O O O O Protons and neutrons 0 Nucleus Atomic of protons Atomic mass protons neutrons Isotope same atomic different mass Ion charged atom How do matter and light interact 1 Emission 2 Absorption 3 Transmission 4 Re ection or scattering Transparent vs Opaque 0 Transparent transmits light 0 Opaque blocks absorbs or re ects light What is color An object re ects some wavelengths of light and absorbs transmits and emits others what we see depends on our eyes and brain 3 basic types of Spectra 1 Continuous Spectrum Thermal Radiation 2 Absorption line spectrum 3 Emission line spectrum How does light tell us what things are made out of Electrons and light 0 Only photons whose energies match the change in electron energy levels are emitted or absorbed 0 With enough energy electron can escape atom completely 0 Only speci c electron energies allowed 0 Absorption or emission happens at very speci c energies Every atom ion and molecule has its own unique spectral ngerprint How does light tell us what temperature things are Thermal Radiation o All everyday objects emit it 0 Only transparent objects don t emit it 0 Spectrum depends on temperature Light per are peaks shorter wavelength as energy increases Two Properties of Thermal Radiation l Hotter objects emit more light at all frequencies per unit area 2 Hotter objects emit photons with a higher average energy Temperature Average Kinetic Energy Thermal Energy total Kinetic Energy How does light tell us the speed of an object The Doppler Effect Red Shift 0 Moving away longer wavelengths Blue Shift 0 Moving towards shorter wavelengths No moving or moving across no shift Measuring red shift is measuring velocity Telescopes Advantages of over eyes 0 Bigger 0 Can add cameras 0 Can see more of the electromagnetic spectrum Bigger is Better 1 Larger light collecting area Area is proportional to d2 2 Better angular resolution a Clarity acuity b Units of angles the small the angle the better acuity Quantifying better 0 Resolution scales like ld 0 Collecting Area scales like d2 Telescope Design 0 Re ecting mirrors 0 Refracting lenses Adaptive optics xes turbulence Chapter 6 In orbit we learn the sum of the mass the bigger of the two in the attraction tells a measurement of the more massive object Solar System is 98 H Order of Solar System Mercury lla hot rockquot Venus quotCloudy Planet also a rock Earth llWater planet has a very large moon Mars llfrozen planet a rock Asteroid belt lots of rocks Jupiter gaseous planet H and He biggest planet orbited by o Europa Ganymede and Callisto 4 moons Saturn giant and gaseous like Jupiter rings are made of ice chunks Uranus tilted planet giantgaseous on 90 degree tilt Neptune almost twin of Uranus without tilt Pluto ball of ice Terrestrial Planets Four rock planets Jovian Planets Gas Planets Virtually all rotational motion is in the same direction Asteroid belt between Mars and Jupiter cy Comets Kuiper belt vicinity of Neptune OortCloud beyond Pluto Nebular Theory Our Solar System formed from cloud of gas 0 Gravity forced cloud inwards and rotation speed increased due to conservation of angular momentum 0 Solar System formation is a stage of galactic recycling What Causes orderly patterns of motion 0 Angular Momentum 0 Conservation of Energy What s the cause of inner rock planets and outer rock planets 0 Conservation of Energy Frost line outside cold enough to form ices inside too hot Accretion gravity draws planetesimals together Asteroids Come from o Leftover planetesimals Existence of moon caused by collisions and impacts Nebular Theory Figure 624 Measuring elements in meteorites indicate age of solar system 46 billion years radioactive decay Planet is 1 million to 1 billion times fainter than star We detect planets around other stars by looking for wobble of the star We measure the wobble using the Doppler shift in the star s spectrum Doppler shift of wavelength measures velocity quotnowquot change in Doppler shift change in velocity acceleration The size of the velocity variation with time tells us the planets mass Higher velocity difference bigger planets mass Period in years of the wobble tells us the radius of the planets orbit through Newton s version of Kepler s third Law P2 agMwslemMsun Detect planets if they eclipse their star Fraction of starlight blocked tells us planets size Kepler Mission 0 Monitoring 100000 stars for eclipses to search for Earthsized planets for 4 years o 001 variation 0 Two Earthsized planets Over 687 known extrasolar planets Most are gas giants more massive than Jupiter and closer to their star than sun to earth 0 Stars and planets do form from interstellar gas clouds o The clouds do collapse under their own weight and form disks No interactions planets don t migrate Chapter 7 How do we predict climate change 0 Computer models 0 Extrapolate trends on Earth 0 Study more worlds under extreme conditions 0 Wait and see what happens Planets as homes for life Mars once had flowing water 0 Mars appear to have ancient riverbeds o Eroded Craters patterns of water 0 Lowlying regions may have had ocean What determines surface temperature 0 The energy emitted by a planet in infrared light equals the amount of sunlight energy it absorbs Conservation of energy 0 Daily variations in temperature depend on a planets rotation rate 0 The intensity of sunlight on a planet depends on its distance from the sun Planets Reflectivity affect temperature what energy is not reflected is absorbed Greenhouse effect 0 Earth s atmosphere absorbs light at most wavelengths 0 Figure 715 molecules let visible light through but absorb infrared photons 0 Certain molecules let sunlight through but trap escaping infrared photons Mars once had a thicker CO2 atmosphere dramatic climate change 3 billion years ago Mars interior cooled off lost its magnetic field atmosphere lost to stripping by early solarwind Venus 0 Thick C02 clouds Earth s C02 is in plants rocks and ocean CO2 dissolves in ocean and gets locked into rocks A runaway greenhouse effect would occur if Earth was at Venus distance from sun Earths Climate changes C02 content of Earth s atmosphere is steadily increasing The rate of increase and the C02 level are both higher now than at any time in the last 400000 years Increased C02 is causing global warming causation established by comparing the model predictions to data The excess carbon is from humans 0 Rate we produce CO2 is greater than ocean can absorb Even if we make changes today the effects are not felt by the climate for a long time delay because C02 sticks around lRunaway Greenhouse Effect occurs when a planet absorbs more energy from the sun than it can radiate back to space Under these circumstances the hotter the surface temperature gets the faster it warms up Scientists detect the signature of a runaway greenhouse when planetary heat loss begins to drop as surface temperature rises Read Chapter 93 Chapter 9 What do asteroids look like 0 The streaks are curved because of parallax caused by Earths orbit 0 Not round have craters Meteroid chunk of rocks Meteor bright tail Meteorite rock from space on earth Meteor shower happens when we pass through dust tails left by comets A comet tails forms as sunlight melts the ice releasing gas particles OortCloud extending 50000 Au random orbit Kuiper Belt orderly orbits 30100 Au in disk of solar system Jovian planets determine where asteroids and comets are today Early bombardment by comets may have supplied most of Earth s water Exam 3 Study Guide Newton s version of Kepler s 3 Law What determines the average orbit speed of a star orbiting the center of the galaxy Answer The mass included inside the star s orbit Super massive black holes Seen by infrared radiation Center of Milky Way Stars indicates a black hole stars orbit this center The more massive the black hole the faster the orbital speed A black hole is any object whose gravity is powerful enough light cannot escape it Event horizon marks the boundary between observable universe and inside the black hole Schwarzschild radius the size of the event horizon Fg m1m2r2 White Dwarf vs Neutron Star Nova White Dwarf and X ray burster explosions Neutron Star on surfaces Doesn t occur in isolated systems energy comes from other star White Dwarf Supernova must reach 14 Solar masses to explode needs mass transfer from binary Massive star supernova is an iron core collapse and result from a high mass star Accretion disk in white dwarf binary system o Occurs when mass spills over from companion to white dwarf and has some orbital velocity and law of conservation of angular momentum dictates clump orbits faster as gets closer to dwarfs surface The inwardspiraling gas in the accretion disk becomes hot as energy is converted into thermal energy Accretion disk in Neutron star in binary system 0 Gas over owing from a companion star can create a hot swirling accretion disk around the neutron star The much stronger gravity of the neutron star makes its accretion disk much hotter and denser than in white dwarf The high temperatures make it radiate X rays Electron Degeneracy Pressure White Dwarf 0 Supported against the crush of gravity Neutron Degeneracy Pressure Neutron Star 0 Neutrons rather than electrons that are closely packed so is called neutron degeneracy pressure Galaxies Spiral all age stars Spheoidal component bulge and halo 0 Disk has organized orbit 0 Halo stars orbit in any direction Elliptical Galaxies 0 Mostly low mass stars 0 Has no star formation Star Gas Star Cycle recycles gas from old stars into new star system Halo Stars 00202 heavy elements very old stars Disk Stars 2 heavy elements stars of all ages Star formation needs cold molecular gas Smaller the parallax angle the farther the star In sphere divide luminosity by area to get brightness Hubble s Law velocity H0 x distance redshift required Standard Candles tells us distance Faster expanding Universe younger universe HR Diagram A stars mass and age determine its other properties Know stellar evolution stories for low and high mass stars High mass star gt 8 solar masses Low lt 8 Solar masses Brown Dwarfs Electron Degeneracy pressure During red giant phase and double shell red giant star is increasing in size Big Bang produced H and He Star production produced everything else Supemovas 7 everything heavier than iron Fe has lowest mass per nuclear particle Early Universe must have been very hot and dense as universe expands collisions become coolerless energy Know ERAS Four Fundamental Forces unify as one at high enough energy 1 Strong 2 Electromagnetic 3 Weak 4 Gravity HeliumHydrogen ratio and Cosmic background evidence for Big Bang The final is cumulative review your midterm results at least once Look particularly hard at the questions you got wrong and at the questions you guessed rig ht a lucky guess may not be so lucky on the final Questions from each midterm will be repeated on the final either verbatim or in a very slightly different form be sure to read the questions carefully Don39t assume they are exactly the same Use the exam reviews on Mastering Astronomy to review practice exam questions The clicker questions are often inspirations for exam questions lectures identify the important ideas Note that answers to the quotquick quizquot questions at the end of the chapter are available in the Mastering Astronomy exam reviews There will be no more than 70 multiple choice question on the final About 10 15 questions will come from Chapters 16 and the rest will be from Chapters 1 15 and Chapter 17 excluding Chapter 8 There will be one optional essay question It will be graded if your computed Course Grade lies on the border between two grades For example if your course grade after the final exam is 895 the decision as to whether you get a 40 or a 35 lies in how well you wrote your optional essay If it shows me you deserve a 40 your grade gets rounded up Otherwise it remains a 35 You have to take the final exam and write an essay to have this opportunity All students who opt not to take the final should expect to get whatever their Interim Grade was which I will compute and post on April 27 For example an 897 will be a 35 in that situation If you want an opportunity to improve the interim grade take the final FINAL EXAM review questions for Ch 16 Relevant review questions for the final Ch 16 End of chapter questions 1 3 5 8 10 36 Ch 17 The topic of deuterium abundance and normal matter will appear on the final exam it wasn39t covered on Exam 3 The cosmic calculation 141 orbital velocity law p 391 is relevant to understanding the evidence for dark matter If the math was on a previous exam example luminosity brightness distance relation it may be required on the final exam The cosmic context figures eg Figure 1617 175 should be extremely useful in identifying and summarizing the major ideas from these chapters Work through the Visual Skills Check p 469 and 497 The answers are in the back of the book Figure 1712 covered in the Visual Skills Check for Ch 17 is challenging but if you succeed in figuring out what it is trying to tell you you will understand how the deuterium to hydrogen ratio measurements limit the amount of normal matter there can possibly be in the universe Here is the chapter 16 slides that will be important for the final I believe 10 questions from this chapter section4 quot asnid5512lSP205002937765EL32381 will be on the 39 39mm 4 I