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Phys 183 – The Milky Way Inside and Out.docx

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Department
Physics
Course Code
PHYS 183
Professor
Tracy Webb

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Phys 183 – The Milky Way Inside and Out o Not a Milky Way, cluster of Andromeda) stars, • Weightlessness: Our Solar System: few Dwarf because due to constant 1. Sun galaxies these state of free fall 2. Mercury • Seasons are due would be o The 3. Venus to the Earth tilt grouping forward 4. Earth of stars velocity and the in 3D, of space 5. Mars orientation to the consolati 6. Jupiter sun, which as it ons are station is 7. Saturn rotates points in equal to 8. Uranus a different grouping the fall of 9. Neptune orientation to the of stars the 10. Pluto + Eris sun in 2D station, (Dwarf planets) • Nebula: a cloud which • Globular of interstellar keeps clusters are gas and dust (i.e missing FACTS: thought to be the • Sun to Earth: 8 oldest objects in Orion) Earth, light minutes the universe o New thus o Sun is orbits. not a first • What is a gen star Scientific Theory? • Earth to closest star (Alpha o Explains centurion): 4 a wide light years stars are variety of • Earth to closest We always see objects formed observati galaxy in the past, the time at from (Andromeda): 2 which light travels (i.e Nursery million light when looking at the sun interstell years we see it as it were 8 ar or • Visible universe minutes in the past) Nebula is 14 billion light from this How galaxies move “dust” years (time light with the expansion of made up has been travelling to us, the Universe: of still things • The further apart fundame on with further but has two galaxies, the ntal few yet to reach faster they are elements simple Earth) receding from • Interstellar principle each other medium: space s • Earth orbits sun o Supporte at 100,00 km/hr • As the visible between the stars d by • Earth has a 23.5° universe • Interstellar off the axis expands, Cloud: denser compelli • Sun rotates the galaxies do too. area (on ng average) on the evidence galaxy once per interstellar o Does not 230 million medium where fail any years at 800,000 crucial km/hr the stars are held test • Local Group: Definitions: together by their Milky Way + • Consolations: own • Thermal Grouping of gravitational pull Energy: Andromeda stars (i.e Orion) thus creating collective kinetic galaxies with a galaxies (i.e energy of many particles (related formed at the • This is because Earth rotates faster than Mars, to temp, but is same time, out thus as we rotate to catch up to Mars it appears not) of the same gas as if Mars moves EW but as we pass Mars it o Depende cloud (but has appears as if it moves WE. nt of fragmented out) temperat  large cluster Ptolemy’s Model (150AD) ure and (farther apart • Epicycles:As the planets rotated around Earth, density stars) older stars they had smaller orbits that they rotated every • Temperature: (due to observable once in a while (W  E) average kinetic • But that still didn’t solve it completely; they had energy of many universe to have epicycles upon epicycles… particles in a expanding) substance • Power: rate of energy flow Joules/Sec • Isotopes: differ in # of neutrons • Ionization: stripping electrons • Evaporation: breaking flexible bonds • Star Cluster: bound group of stars which Determining the circumference of the Earth (240BC): The shadow was 7° from the Zenith and 0° from Syrene. The distance between Zenith and Syrene is 5000 stadia. It can be concluded that: 7°/360° x Earth Circum = 5000 stadia Earth Circum = 250, 000 Stadia Greek Model of the Universe: • Earth is at center of universe (Geocentric Model) • Heavens are perfect (Spherical objects) • Evidence that support this theory: o Sun and stars appear to move around the Earth o No perceptible movement of earth • Philosophy: o Insisted on Mathematical perfection (i.e whole #s, perfect spheres) o But they had evidence that did not follow their model Retrograde motion: Planets usually appear to move E  W but occasionally reverse direction • This observation had a hard time explaining the geocentric model • They had to offset Earth from the center to allow 1. for this model. Copernican Revolution 1. Nicolas Copernicus: a. Reintroduced the helicocentric model i. Sun is at the center of universe ii. Still insisted on spherical orbits b. Huge paradigm shift called the Copernican Principle 2. Thyco Brahe a. First to gather data about the heavens b. Build first astronomical observatory c. Did not observe stellar parallax: concluded earth must be stationary 3. Kepler: Objects moves with a constant velocity unless a net a. FIRST LAW: Planets rotate in ellipses force acts upon it 2. Force = ma, the amount of acceleration depends on an object’s mass and force exerted upon it 3. For any force, there is an equal force in the opposite direction a. This is the reason why rockets can move, as the fuel coming out pushes on Earth, an equal force pushes on the rocket. b. We exert an equal force that earth does on b. SECOND LAW: Planets sweep equal us (but Earth is so massive) areas in equal time c. THIRD LAW: More distant planets to Conservation of momentum explains why Earth keeps rotating around the Sun Sun, the 2lower the orbit o Angular momentum: M x V x R i. P (unit: yr, rotate around sun, Gravitational potential energy: Earth = 1) = a (unit:AU, distance to sun, Earth = 1) o Depends on object’s mass, strength of gravity 4. Galileo and distance between the two objects a. 1 to observe heavens with a telescope o Collapsing cloud: Mass stays constant but the distance b. Pointed 3 main objection to the Copernican View: i. Earth cannot be moving because objects in the air would be left behind a. He showed objects in motions stay in motions unless stopped by external force b. Reason why we don’t fall decreases thus the gravitational pull increases behind as Earth rotates causing the cloud to heat up  ii. Heavens are not perfect o Only way to decrease disk size of galaxies is to  increase kinetic energy thus decreases the  a. Saw craters and mountains on Moon potential (orbit size) b. Sun Spots Mass Energy: 2 iii. If Earth rotates the Sun, we o E = MC should detect stellar parallax o Small amount of mass can have lots of energy Kepler + Newton: Newton’s Law of Motion: missing bands tell you the elemental composition of the sun. Escape Velocity: o El o Enough velocity to escape Earth’s gravitational ect pull ro o Earth escape velocity is 11km/s nic Earth’s Tides: o Full Moon/ New Moon both moon and sun pull together on Earth and since water moves easily large tides are created o Quarter moons do not act with the sun and thus smaller tides are created Why objects fall at same rate energy levels contain rotational (very small in energy different) and vibrational energy o Objects change colour depending on the thermal energy within the object Things to remember about light: o Absorption/emission o Transmission/reflection o Wave and particle o Wavelengths o Frequency o Speed o Magnetic and electric waves that are orthogonal 3 Types of Spectra: 1. Emission lines: wavelength energy that is emitted from an object a. Downward transition, potential energy of Thermal Radiation electrons is released o Any objects above absolute zero emit radiation 2. Continuous spectra: spectrum of light bulb spans o Thermal radiation is ONLY DEPENDENT on all wavelength of visible light TEMPERATURE 3. Absorption lines: wavelength energy that is o Hotter objects emit more energy; Brighter absorbed from an object o Hotter objects emit photons with higher average a. Upward transition, potential energy of kinetic energy (smaller frequency) electrons increased The Doppler Effect: Each atom has a unique set of energy levels; each o Used to measure velocity transition corresponds to a unique frequency, wavelength and energy o Ashift in frequency of a wave due to motion of the object Thus depending on the emission spectra one gathers from an object, one can determine the composition of it. Sun solar spectrum: o It creates a full continuous spectrum in the core, as light travels to the outside layers it interacts with the different elements present. These elements can absorbed certain wavelengths, thus the emission solar spectrum is not fully continuous and is missing a few bands. The o An object moving toward the observer, a with a temperature when it escapes - which is the shift toward smaller wavelength will be observed temperature we see It takes thousands of years for one photon to escape the detected o An object moving away from the sun’s corona observer, a shift toward larger wavelength will be detected Solar Neutrinos: o An object moving at an angle from the o Rarely react with other matter o You need 1 light year of lead to stop 1 neutrino observer will only detect the component that is moving toward or away o Neutrinos pass through the layers of the sun as if o Depending on the shift, one can determined the it were empty space direction and velocity of the object. o Early detection of neutrinos could o This same phenomena occurs for rotating objects only account for 1/3 of the predicted solar neutrinos o One can determine which way it rotates 37 because as it rotates away from you the o 100,000 gallon tank of Cl in a mine spectra will be shifted toward a redder would react with neutrino to give Ar wavelength and vice versa. o Amount ofArgon was then counted Gravitational Equilibrium: o There are 3 kinds of neutrinos o Gravitational Equilibrium keeps the sun’s core o Electron hot and dense enough to maintain nuclear fusion o Muon reactions o Tau o Core is about 15 million K, photosphere is o Sun produces electron neutrinos 6000K, chromosphere is 10,000K and corona is o Of these 2/3 change into muon and tau 1 million K  neutrinos before reaching earth o Sun is mostly made up of hydrogen and helium Properties of telescopes Fusion & Fission: 1. Light Collecting are o Fusion is 4 hydrogen atom collide to make 1 a. Larger the collecting area can gather helium atom greater amount of light in a shorter time o Large kinetic energy is needed to surpass (can see fainter objects) the electromagnetic repulsion of the two b. This depends on the area of the dishA= nuclei pi*r2 o This releases energy which accounts for c. Largest optical telescopes are 8-10 meters the mass difference between 4 hydrogen in diameter to 1 helium atom 2. Angular Resolution: o Occurs trough the Proton-Proton Chain a. Having the ability to discriminate  First 2 protons collide to form a between two very close 2D objects deuterium nucleus, H 2+ b. θ = 1.22λ/diameter c. We can mimic a large  2 deuterium collide to form helium-3 telescope through  2 helium-3 collide release two telescope arrays Deuterium and forming one Atmospheric Turbulence Helium • Turbulence in the atmosphere (dust particle) distorts the image and  Each collision releases energy in gamma rays and neutrinos causes image to blur and stars to twinkle o Fission is the breaking of 1 helium atom into 2 • The limit resolution is thus limited to 1arcsecond hydrogen atoms from the ground • Advantageous to have telescopes: Nuclear fusion occur at the core, the gamma rays then o High in altitude make its way to the outer layer in a drunken walk o Dry area (random pattern) o Best to have them in space (removes all As the photon travels out, it collides with other particles turbulence) and dissipates some of its energy, the photon ends up • Radio and optical light pass in generous amount through the atmosphere Information from telescopes: emission is closer to the infrared spectrum (even • Images: what you would see with powerful eyes, though the core is hotter) • This keeps occurring (when He runs out, heavier different colours using different filters. Can use different wavelength (radio, x-ray) and get elements start to fuse), at one point the outer different pictures layers are just blown off the star (and the star • Spectroscopy: gather light and pass it through a looses a lot of mass) and moves down from the prism to separate the different emitted main sequence to become dwarfs (run out of wavelengths and determine what is present fuel) • Timing Information: the relative brightness an object changes over time (as it rotates) or move Determining age of star from HR away from one diagram: • Stars on the The Hertzsprung-Russell Diagram main sequence have a certain • This chart (1/Temperature vs. Luminosity) allows us to classify stars lifetime (top left • One can observe that most stars fall within the corner, lifetime is main sequence, which is the relationship between short) sizes of stars, their temperature, and thus their • One can determine the age of stars off luminosity; is linear. the main sequence • However Giant stars and dwarfs do not fall within this main sequence by determining the • Axis based on our Sun (luminosity = 1 and temp age of the star that = 6000K) is still present on the main sequence but is part of the stellar clock. • Our sun falls within the main sequence • Since these starts were created at the same time, • The main sequence implies that these stars are their age is the same even though the rate of undergoing Hydrogen Fusion • Luminosity is proportional to Mass 4 hydrogen fusion is different. o Smaller stars: cooler and fainter longer Stellar Evolution lifetimes 1. Where do stars form? o Higher mass stars: hotter and brighter a. Interstellar Medium: The gas and dust shorter lifetime between starts • Lifetime is based on how much hydrogen is b. The more the image is black the more being fused per time dust there is which blocks the light • Luminosity – Radius – Temperature relationship: c. Newborn starts are found in very bright L=4πR T 2 4 area of the interstellar medium • Giants/SuperGiants stars are large but cooler Interstellar Dust: • Dwarfs are small but much hotter • Tiny solid particle Giants/SuperGiants/Dwarfs • 1 micron in size (Carbon, Silicon, Iron, Oxygen) • Hydrogen matter has run out (no hydrogen • Blocks light • Infrared light observation can reveal the new star fusion) • Only higher mass matter is present (greater within (because the GMC is very cold) gravitational force), the core contracts and heats up (allowing the next heavier element (He) to Within the interstellar medium the Giant Molecular start fusing) and the outer layer puffs out (star Cloud (GMC) is where exactly the star will form • Most matter is Hydrogen and CO gets larger) • This then becomes giants/supergiants stars • Temperature is extremely cold (10-30K) because the luminosity/temperature that is • Small density (300 molecules per cubic cm) observed is that of the outer layers, since these layers are further out from the core the matter Glowing Dust Grain: consisting of the outer layer are cooler and the • Dust grain can absorb energy from GMC (very M M1 2 cold, long wavelength) and emit wavelength in o Remember: F g 2 , the denser r the infrared (the smaller r) the greater the gravitational pull 2. Why do stars form? • Random motion of matter in the GMC begin, Stages of Star Birth this creates heterogeneous density within the 1. Contraction cloud. • Dense area of GMC have a hard time to • Areas of high densities will begin to exert a allow emitted energy (radio/infrared) to strong gravitational pull between the escape (as soon as it is emitted it is absorbed molecules by another molecule) • In the gravitational force is greater than the • This therefore maintains the thermal pressure pressure force (outwards) then the cloud will of the cloud to match gravitational force and collapse getting smaller and denser (warming contraction of the GMC is halted  this object up) is known as a • Each dense area has the ability to create a protostar new star  this leads to fragmentation of the • The GMC will denser cloud area continue to grow o Dense fragments have the ability to as it gather new form new stars material form its o GMC can form thousands of stars surroundings. 2. Rotation Gravity Vs. Pressure: • All GMC have some small overall rotation • Gravity brings molecules together (angular momentum) • Pressure forces the molecules apart • Newton’s 1 law: Conservation of momentum (first law) is applied, but as the o When stars begin to form, this pressure is known as Thermal Pressure cloud contracts or shrinks in diameter the • If gravity wins, particles will begin to exert object gains angular momentum: greater kinetic energy and the gas will heat up ρ=mx v x r • Energy can be release from the rotational o Gravity usually wins because as the axis of the rotated GMC density of the particle increases, the particles begin to have greater kinetic 3. Nuclear fusion energy and thus absorption of energy • Before hydrogen fusion occurs, the object occurs. will move around the HR diagram as they o Molecules that are excited soon go back change size/temp (surface) • As hydrogen fusion kicks in the young star it down to their ground state simultaneously emitting energy in the form of moves into the main sequence wavelength (because the cloud is in the • Depending on the mass of the star, the life- early stage of star formation, the cloud is tracks will vary cold thus the wavelengths are in the • Massive stars are rare, many more stars infrared spectrum) which are at lower mass (all in respect to our o The release of this thermal energy own sun) (pressure) allows gravity to be greater • Requires temp of 10 K for H-fusion than the pressure allowing the GMC to collapse even further and for this process to repeat itself Electron Degeneracy Pressure (EDP) • Quantum mechanics say that 2 electrons cannot o As these steps are repeated the average
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