exam #2 study guide
exam #2 study guide ASTR 121
Popular in ASTR 121 The Solar System
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This 16 page Study Guide was uploaded by Anisa sudra on Wednesday May 20, 2015. The Study Guide belongs to ASTR 121 at University of Oregon taught by Scott Fisher in Spring 2015. Since its upload, it has received 126 views. For similar materials see ASTR 121 The Solar System in Astronomy at University of Oregon.
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Date Created: 05/20/15
Photo of the day Moon la luna moon ower 0 Infrared and ultraviolet picture of encleadus observed by cassini o The ultraviolet is what highlights the texture and ridges 0 photo of encelaudus to scale in reality everything is various sizes They just show similar sizes in photos 0 Major Moons around the system of Sol within the solar system 0 Finding life best case europa and enceladus Moon phases 0 28 days for the moon to go around the earth 1 month if you keep constant track of the moon you see more and more of the moon as the month progresses Moon goes thru a cycle once a month in which we can predict for years Why do we see phases of the moon I Lunar phases are a consequence of the moon s 273 day orbit around earth a As the moon orbits we can see more and more of the side that is lit by the sun a Moon 15quot away from earth on quotgrapefruit scalequot a From earth to the moon 25 million miles 0 Sun is 400x further away than the moon Why do we see phases of the moon a Half of the moon is illuminated by the sun re ected sunlight and half is dark It makes no light itself a We see a changing combo of the bright and dark faces as the moon orbits earth a New moon up during the day and we can see it bc the sun is so bright it makes the sky brighter and bc we are looking at the side of the moon that is not illuminated a Full moon when we can see the illuminated side a Quarter moon quarter of the moon is illuminated etc Phases are just different parts of the moon we can see that are being illuminated we only see one side of the moon a synchronous rotation the moon rotates exactly once with each revolution around the earth 0 This is why only one side is visible form earth 0 The earth and the moon are tidally locked the back side of the moon photo which was taken behind the moon as the spacecraft ew around it this shows the side of the moon that never faces the earth due to synchronous rotation n this quotdark sidequot isn t darkjust the other side 22 the reason for seasons 0 the real reason for seasons is the tilt of the earth s axis 0 The altitude of the sun changes with seasons 0 O 0 Sun 5 position a noon in the summer higher altitude means more direct sunlight The shape of the path of the sun analemma Sun 5 position at noon in the Winter lower altitude means less direct sunlight 0 look at image in book for graphic Seasons depend on how earth s axis affects the directness of sunlight How does the orientation of earth39s axis change with time o The axis precesses over about 26000 years Which means Polaris wont always be the north star 0 PRECESSION o The 2 systems of constellations are no longer aligned 0 Reason why astrology does not work 0 The stars move over time therefore the stars when you were born are not in the same place they are now WEDNESDAY 42915 Video driving on the moon Reading assignment Read ch 3 esp 34 Read ch 5 esp 53 Extra credit Hw 4 o Astro blog 34 the Nature of Science 0 goals 0 how can we distinguish science from nonscience Or more importantly a psedoscience o What is a scienti c theory Science vs non science 0 The word comes from the latin scientia meaning knowledge 0 Not all knowledge comes from science The idealized scienti c method 0 Based on proposing and testing hypotheses o Hypothesis educated guess 0 Add notes from slides FRIDAY 5115 Hallmarks of science 1 Modern science seeks explanation for observed phenomena that rely soley on natural causes 0 A scienti c model cant include Hallmarks of science 2 Hallmarks of science 3 A scienti c model must made testable predictions about natural phenomena that would force us to revise of abandon the model if these predictions do not agree You must start over THEORY has different meaning in science than in everyday life o in science a theory is no the same as a hypothesis A scienti c theory must 0 Explain a wide variety of observations with a few simple principles 0 Be supported by a large compelling body of EVIDENCE NOT have failed any crucial test of its validity HCW distinguish science from non science HCW Chapter 53 TELESCOPES Extra credit observatory extra credit kiosk in eug due may 15 CHAPTER 53 Photo of the day gibraldi Mauna kea is no longer the biggest 0 They collect more light than our eyes light collecting area 0 See more detail than our eyes angular resolution 0 They can detect types of light like infrared or x rays that are visible to our eyes better wavelength coverage bigger more light collecting area and better angular resolution the bowl shape in all telescopes focus light we have to have different types of telescopes to observe different parts of the spectrum w radio telescopes you can take multiple dishes and link them up as if they were one single telescope Basic telescope design Lenses Makeup pupil eyepiece focus objective lens incoming light Older type Mirrors bigger mirror more detail all research telescopes today are re ecting Newer Hi b Subaru name of the constellation pleadies in Japanese GTC gran telescopio canarias 104 segmented mirror 0 computers can only take care of these mirrors I 0 light pollution 0 there is too much on the earth too bright to see anything 0 turbulence causes twinkling angular resolution 0 blurs images 0 based on earth v based in space 0 the atmosphere absorbs most of EM spectrum including all UV and X ray and most infrared O Web projects 59 or 60 or 61 o 12 pages about the observatory Include an image or 2 0 Include citations Globeatnightorg 0 Worldwide project that measures how much light pollution there is 0 Air is opaque to mose wavelengths of radiation There are only a few windows where radiation like sunlight can make it to the surface of the earth 0 The visible window is where our eyes operate 0 Location in space overcomes the problems of light pollution and turbulence Nothing short of going to space can solve the problem of atmospheric absorption of light 0 The big problem is that they are very is expensive 1 hubble 20 gemini telescopes A secondary issue is with 39adaptive optics AO systems big telescopes like Geminikecktmt will rival space conditions 0 Rapid changes in mirror shape compensate for atmospheric turbulence This technique allows two it more small telescopes to work together to obtain the angular resolution of a larger telescope 52 learning from light goals gt 0 how does light tell us what things are made of A thin or low density cloud of gas emits light only at speci c wavelengths that depend on its composition and temperature producing a spectrum with bright emission lines o A cloud of gas between us and a light bulb can absorb light of speci c wavelengths leaving dark absorption lines in the spectrum Each type of atom has a unique spectral line EXAM 2 FRIDAY MAY 22 101 A closer look at the sun GOALS Why does the sun shine What is the sun s structure WHY DOES THE SUN SHINE the amount of energy that the sun gives off each second Is the sun on re No If it were Chemical energy contentluminosity 10000 years Is the sun contracting No If it were Gravitational potential energyluminosity 25 million years The sun is powered by nuclear energy Nuclear potential energy coreluminosity 10 billion years 0 only nuclear reactions can provide energy for long enough a ow of charged particles from the surface of the sun There is a wind of these particles coming off of the sun this is what protects us from the solar wind Without the magnetic eld we would have MUCH stronger effects from the sun on Earth outermost layer of solar atmosphere 0 1 million K no one knows why it is this temp visible surface of the sun 0 600 K o the surface of the sun appears and is granular where energy is generated by nuclear fusion 0 15 million K 103 The SunEarth Connection GOALS What causes solar activity What causes solar activity 0 Magnetic eld of the sun Solar activity is like weather on Earth Sunspots Solar ares Solar prominences Areas on the photosphere that are cooler than other parts of the sun s surface 400 K 0 These regions have strong magnetic elds 0 Loops of bright gas often connect sunspot pairs Caused by magnetic activity that sends bursts of x rays and charged particles into space 0 Magnetic activity send bursts of energetic charged particles out through the solar system a 1112 year cycle that has something to do with the winding and twisting of the sun s magnetic eld 0 Where activity rises and falls Chapter 13 o All of the elements on the periodic table except for H He Li is star stuff Once Hydrogen fusion slows down it ends with a pulse that ejects the H and He into space 0 The core led behind becomes a white dwarf o The White Dwarf illuminates the material causing it to glow as a planetary nebula White Dwarfs o The exposed Carbon core of a dead lowmass star that shed its outer layers in a planetary nebula 0 Electron degeneracy pressure supports a white dwarf against gravity 0 Sirius is also known as the Dog Star 0 The exposed Carbon core of a dead lowmass star that shed its outer layers in a planetary nebula 0 Electron degeneracy pressure supports a white dwarf against gravity 0 A white dwarf is about the same size as Earththey are VERY dense o 05 14 MSun packed into a sphere the size of the Ea h 0 300000 Earth masses in the same volume 0 a teaspoon of white dwarf maaer would weigh several tons on Earth pressure force per unit area on container When you remove the heat source gas cools down pressure drops gas gets more dense Pressure provided by electrons due to the effects of quantum mechanics A white dwarf that is supported by electron degeneracy is at almost the minimum volume that an amount of mass can be compressed into all the electrons are quotalmost touchingquot All available energy levels below a certain value are full so many highenergy quothotquot electrons cannot cool down lose energy 0 l they stay quothotquot even if there is no heat source Those quothotquot electrons provide the pressure that supports White Dwarf Quantum mechanics says that electrons that are very close to each other cannot have the same energy that means electrons can only get so close to each other and no closer Adding mass to a white dwarf increases its gravity forcing electrons and nuclei into a smaller and smaller space Is there a limit to how much you can shrink a white dwarf YES The Chandrasekhar Limit is when a white dwarf has a mass of 14 mes the mass of the Sun 14 Msun At this point the inward pull of gravity overwhelms outward pressure of electron degeneracy and the white dwarf collapses and goes supernova Collapse raises WD core temperature rapidly above 600 million K runaway carbon fusion begins and WD explodes Such an exploding WD called a white dwarf supernova A WD supernova attains a luminosity of 10 billion Suns lComplete explosion of WD nothing led behind 132 JUPITER AND FRIENDS Messier 35 0 Open star cluster about 2800 light years away 0 1500 stars these stars are orbiting around each other 0 in a disk of the milky way 0 2nCI cluster is NCG 2158 globular cluster 0 bigger star cluster Jupiter 0 About 38 light minutes away OUR COSMIC 39HOOD Most stars we see are 10500 light years away 0 Most nebulae and open clusters are 100020000 light years away 0 Milky way is 100000 light years in diameter LIFE OF A HIGH MASS STAR 0 Have a majority of the stuff that we re made out of THRE AER 2 TYPES OF DEGENERATE OBJECTS 0 White dwarf 0 Supported by electron degeneracy pressure you can only pressure electrons so far this is what keeps the white dwarfs from being crushed This is the leftover core of low mass star like the sun these will always have a mass of lt 14M sun Neuron star 0 O O 0 Is the ball of neutrons left behind by a massivestar supernova Supported by neutron degeneracy pressure The leftover core of a high mass star with a mass between 14M sunlt M lt 3M sun A neutron star is about the same size as a small city How were these stars discovered Pulsars n Jocelyn bell accidentally discovered the radio source in vupecua n A sharp pulse recurred every 13 seconds a Determined to be 1000 light years away and called it a pulsar n this was discovered in the heart of the crab nebula and it also pulses in visual light a They are the lighthouses of our galaxy Anything heavier than 3M sun becomes a black hole 0 Black hole object whose gravity is so powerful that not even light can escape it 0 O O O The gravity is so strong it distorts the space around it Event horizon spherical surface of the black hole that is the radius at which the escape velocity equals the speed of light Schwarzschild radius the radius of the event hodzon According to einstein s general theory of relativity gravity is really the warping of space time about an object w a mass This means that even light is affected by gravity bc light travels thru time Spacetime is warped by bigger objects WHAT RE NEUTRON STARS MADE OF NEUTRONS Incredible heat and energy of collapsing core forces electrons to combine with protonstorn apart iron nuclei making neutrons and neutrinos O THERE ARE 2 TYPES OF SUPERNOVA 0 White dwarf supernova type 1 0 Carbon fusion suddenly begins when a white dwarf in a close binary system exceeds chandreasekhar limit causing rapid collapse and explosion Massive star supernova Type 2 o For masses gt the neutron star limit 3Msun no known force can resist the crush of gravity 0 As far as we know gravity crushes all the matter into a single point known as a singularity
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