Final Exam Study Guide
Final Exam Study Guide AST 101 - M001
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AST 101 - M001
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This 20 page Study Guide was uploaded by Mitchell Jones on Tuesday December 8, 2015. The Study Guide belongs to AST 101 - M001 at Syracuse University taught by C. Armendariz-Picon in Fall 2015. Since its upload, it has received 858 views. For similar materials see Our Corner of the Universe in Astronomy at Syracuse University.
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Date Created: 12/08/15
1 AST 101 Final Study Guide Celestial Sphere Stars are so far away, to naked eye seem same distance Imaginary “sphere” on which stars lie “Star Theater” Stars are projector that shine through screen (celestial sphere) to people Constellations Patterns of stars on celestial sphere Represent regions of sky or celestial sphere (like counties or states of sky) Cannot see stars on celestial sphere below the horizon (where ground meets the sky) Horizon in boundary of celestial sphere because the difference between a person’s perspective and the horizon are negligibly small compared to the size of celestial sphere Motion of the Night Sky: Latitude: measured as North/South; lines go east/west Distance from equator Determines climate Altitude (angle between celestial pole and horizon) of Polaris is equal to your latitude Longitude: measured as East/west; lines go North/south Distance from prime meridian (Greenwich, England) Stars move counterclockwise around Polaris (as seen from earth) Stars rise in east and set in the west Circumpolar—stars that are always visible; never rise or set 2 Motion of the Sun The earth spins; celestial sphere is imaginary—it does not spin (stars in fixed position and earth rotates underneath) Earth spins counterclockwise Sun: Is also represented by celestial sphere Rises in the east, sets in the west as earth spins counterclockwise Noon: sun is at highest position in the sky, directly south As year progresses, the sun travels counterclockwise along the celestial sphere Path the sun takes along the celestial sphere is known as the ecliptic Zodiacal constellations—constellations ecliptic travels through Difference between the ecliptic and the celestial equator 23.5 degrees The Motion of the Night Sky (Continued) Celestial sphere rotates once/day Sun moves along ecliptic once/year Sumer solstice—June 21; longest day of the year; sun highest in the sky Autumnal/fall equinox—September 21; 12 hours da, 12 hours night Winter solstice—December 21; shortest day of the year; sun lowest in the sky Vernal/spring equinox—March 22; 12 hours day, 12 hours night In reality, the orbit of the sun on the ecliptic is because of the orbit of the earth around the sun The difference between the ecliptic and the celestial equator is due to earth’s titled axis Earth revolves counterclockwise around the sun Two simultaneous motions: 3 Earth spins counterclockwise on axis, making the celestial sphere appear to spin counterclockwise Earth orbits sun counterclockwise, sun moves counterclockwise around celestial sphere Motion of the Planets Sidereal day: Time it takes stars to complete one full cycle through the sky Time it takes the planet to rotate 360 degrees 23 hours 56 minutes on earth Solar day: Time it takes the sun to return to the highest position in the sky 24 hours on earth Longer than sidereal day because earth has to rotate an extra amount to return to face the sun (earth is orbiting as it rotates) Wanderers: Planets or “wanderers” rise in the east and set in the west, but also seem to move across celestial sphere like the sun “Planet” comes from Greek “planan”—to wander Retrograde motion—when a planet appear to travel backwards across celestial sphere; observed over weeks/months “retro”—to go back reveals illegitimacy of the celestial sphere Early explanations for retrograde motion: Ptolomaeic Model: Earth centered (geocentric) Epicycle—the planet does loops while rotating around the earth Inaccurate—doesn’t explain the phases of venus Sun centered model (heliocentric): Innerplanets orbit fast than outerplanets 4 Retrograde motion occurs because earth passes the other planets in orbit, making them appear to travel backwards as earth gets closer, then back again as it passes The Seasons Origin of the seasons: Due to tilt of earth’s axis Winter—northern hemisphere points away, summer towards Reversed for southern hemisphere (Winter in northern is summer in southern) Spring and fall—perpendicular to sun Distance between sun and earth has no relation to seasons In December, sun is closer to earth, summer sun is further—no correlation Phases of the moon: Moon is a natural staelite of earth Orbits about once a month Rises in east, sets west Due to earth’s rotation Phases: Waxing: illumination getting bigger until full Waning: illumination gets smaller until new moon Crescent: illumination small Gibbous: illumination bigger Position of moon relative to sun and earth responsible for moon’s phases New moon: dark moon (can’t see from earth) 5 Moon orbits earth counterclockwise First quarter moon (first half after the new moon): right side illuminated Full moon Third quarter (first half moon after full moon): left side illuminated Moon’s orbit tilted Moon’s light moves clockwise—picture a cap covering the moon, it must be moved clockwise to simulate the shadows Moon rises and sets in twelve hours (highest six hours after rising) Rises on average 50 minutes later each day because the earth has to rotate a little bit more each day to bring it back to see the moon in its orbit Phase Rise Highest Point Set New 6 a.m. Noon 6 p.m. First Crescent 9 a.m. 3 p.m. 9 p.m. First Quarter 12 Noon 6 p.m. Midnight First Gibbous 3 p.m. 9 p.m. 3 a.m. Full 6 p.m. 12 Midnight 6 a.m. Last Gibbous 9 p.m. 3 a.m. 9 a.m. Last Quarter Midnight 6 a.m. Noon Last Crescent 3 a.m. 9 a.m. 3 p.m. Eclipses: Lunar eclipse: earth casts a shadow on the moon Must be a full moon Total lunar eclipse: moon is entirely in shadow Partial lunar eclipse: part of moon in shadow Penumbral lunar eclipse: moon passes through the penumbra (secondary shadow) 6 Solar eclipse: moon casts shadow on earth; can’t see the sun Total: in umbra (main shadow) Partial: occurs in penumbra Annular: if moon’s shadow does not reach earth, an annular eclipse occurs in small central region on earth Doesn’t occur all over earth, only in specific region Predicting eclipses proves that our model of the solar system is accurate Force of Gravity: Describing motion: Position: location of object Velocity: speed with respect to direction and how position changes Acceleration: speed that velocity changes and in what direction Planets accelerate as they orbit because they constantly change direction (going in an ellipse) but remain at constant speed Newton’s Laws of Motion 1.) In the absence of a net force, an object will move with a constant velocity 2.) Acceleration experienced by an object is proportional to the force acting on it (F=ma) 3.) For every action, there is an equal and opposite reaction Gravity: Force responsible for keeping celestial bodies in orbit Keeps us on surface of the earth Explains evolution of whole universe Laws of nature are universal Universal law of gravitation: Tells us the strength of gravity between two objects (Fg=G[(M1M2)/d^2] D=distance between two objects M=mass of objects 1 and 2 G=gravity constant 7 Greater distance, smaller gravitational force Force Gravity II Newton’s 2 law: F=ma Universal Law of Gravitation: F=(GMm)/d^2 Falling: ma=(GMm)/d^2 a=(GM)/d^2 Powers of 10: 10^n=10*ntimes 10^(n)=1/10^n 10^n*10^m=10^(n+m) 10^n/10^m=10^(nm) (10^n)^m=10^(nm) 10^3=kilo—k 10^(3)=milli—m 10^6=mega—M 10^(6)=micro—µ 10^9=giga—G 10^(9)=nano—n 10^12=tera—T 10^(12)=pico—p 1 mile=1.6 km Parallax Stellar parallax: star appear to change position Earth rotates around sun, so you see stars from different locations in orbit Parallax angle (p): measure of distance to nearby star Angle you have to adjust telescope between its greatest periods is 2p (6 months apart) 8 Larger distance, less parallax Angles: 1 degree=60’ (arc minutes) 1’= 60” (arc seconds) Stellar Parallax and Distance: d(parsec)=1/p(arc sec) 1 parsec= 2*10^13 miles Solar System All planets orbit counterclockwise Elliptical orbits, but practically a circle Nearly all planets rotate counterclockwise, expect Venus Terrestrial Planets—Mercury, Venus, Earth, Mars Small in mass and size Made of rock and metal No rings, few moons Jovian Planets—Jupiter, Saturn, Uranus, Neptune Large mass and size Mostly H and He Rings and many moons Asteroids Small rocky bodies orbit sun Mostly found in asteroid belt between Mars and Jupiter Comets Small icy bodies Found in Kuiper Belt 9 Pluto—does not fit characteristics, dwarf planet Terrestrial Planets Metal core, mantle, rocky crust Earth: Geological Activity Seismic waves caused by earthquakes help us determine internal structure Core is part liquid and hot Planets heated when formed Radioactive decay also heat up interior Cool down over time—smaller planets cool faster Hot interior main driver for geological activity Volcanoes and plate tectonics and earthquakes (pwaves) Pwaves—longitudinal waves travel through core Swaves—stopped by core Volcanoes: Molten rock from earth’s interior reaches surface Release lava, water vapor, CO2, N—outgassing Atmosphere is a product of outgassing Plate Tectonics: Lithosphere divided in tectonic plates that float on mantle Convection causes tectonic plates to shift—creates mountains, valleys, seas Magnetic Field: Charged particles moving in molten, electrically charged metal core creates mag. Field Protects us from wind of charged particles coming from the sun Some get trapped close to poles—cause auroras Protects atmosphere from being stripped away 10 Atmosphere: Protects from solar radiation Captures part of energy coming from sun and warms planet Visible light reaches earth, UV and Xrays are absorbed Greenhouse gases capture heat and warm planet Moon: No atmosphere No signs of present geo. Activity Too small—cooled too fast Density less than earth Probably resulted from big impact with a MarsEarth sized object Craters: Impact mark left by asteroid/comet hitting surface Believed responsible for dinosaur extinction Geo. Activity erases craters on earth Shaping Planet’s Surface: Impact of craters Volcano eruptions Disruption of planet’s surface by tectonic plates Erosion by winds, water, ice Mercury: Smallest planet Similar to earth’s moon No atmosphere No volcanic activity but signs of pat geo activity—cooled fast Venus: Earth sized Rotates clockwise 11 Thick atmosphere—strong greenhouse effect Day and night extremely hot Air pressure same as .5 miles below earth’s ocean Mars: About half size of earth Very thin atmosphere Temp below freezing (58 degrees F) Most similar to earth Evidence of water flows in past and present Jovian Planets Jupiter, Saturn, Uranus, Neptune Jupiter Structure: Under pressure of the material above it in its makeup (atmosphere down to core), H changes phases as you get closer to core Under increasing high pressure H heats up Layers of Jupiter (from top to core): cloudy atmosphere, H gas, H liquid, metallic H, core Metallic H is liquid and conducts electrical charges Jupiter under Pressure: Like stacking pillows—adding more will increase height but will eventually condense and increase density Jupiter’s Magnetic field: Strongest of planets in solar system Auroras can be seen at the poles Jupiter’s Atmosphere: At least 3 distinct layers Ammonia (yellowish), ammonium sulfate (redorange), water vapor 12 Gives Jupiter its color Jupiter Storms Fast rotation (9 hour days) cause winds that reach 250 mph Numerous storms can be seen on Jupiter Great red spot—storm twice size of earth, has lasted for centuries Jupiter moons: more than 60 Europa: large amount of iced water Signs of geological activity and tidal heating suggest huge oceans below surface Io: elliptical orbit causes continual changes in strength and direction of tidal force from Jupiter Flex Io’s interior and cause tidal heating Saturn: Rings: small water ice particles Each particle orbits like moon Ring formation: Likely originate from small moons orbiting Saturn New particles released from collisions between moonlets and other objects Saturn’s gravitational force prevents moons from forming larger bodies Formation of Solar System Important clues: Patterns of Motion Circular planetary orbits on same plane Planets orbit sun in same direction Most planets rotate in same direction as orbit Tilts generally small 2 types of planets 13 Terrestrial: rocky and metal surface Small and dense Jovian: large and less dense Mostly H and He Asteroids and comets Asteroids: small rocky bodies mostly found in asteroid belt Comets: small icy bodies found mostly in Kuiper belt and Oort’s Cloud Nebular theory: solar system formed from gravitational collapse of gas cloud Nebula: gas cloud produced from explosion from dead previous star Diffuse and cold cloud of gas (mainly H and He but some heavier elements) Star Dust: origins of Universe H and He only elements manufactured in early universe Heavier elements produced by previous generations of stars We are all star dust Collapse: Gravity causes cloud to collapse under own weight As it collapses: temp increases (energy conversion)—hottest at center, coldest at boundary Rotate rate increases (angular momentum conservation) It flattened Sun and planets formed in this spinning disk Flattens because it’s easier than collapsing inward (ball on spinning plate example) Pressure very large at center—increase temp (H and He will fuse and form star) When planets form they follow motion of spinning disk Why Planets Form: Condensation Sun formed at center of cloud—increase temp ignites nuclear fusion Planets developed from planetary seeds formed by condensation 14 Temp of disk determined materials able to condense and develop into planets (highest temps needed to produce metals, then rocks, H compounds, H and He gas) Frost line Heavier H rich planets able to form beyond frost line Small, metal rich planets formed within frost line Explains terrestrial and Jovian planets Accretion Encounters between condensed seeds led to larger objects “accretion” Some of these planetesimals eventually grew into planets Clean up Radiation from sun and solar wind cleaned up remaining gas not bound to planets in nebula Asteroid belt is made from leftovers of planetary formation within frost line Jupiter too large for planet to form there (too large gravitational force) Kuiper belt and Oort Cloud contain leftovers from beyond frost line Light Light is electromagnetic radiation: wave of electric and magnet fields Light produced by moving electric charges (electrons) Light changes motion of electric charges Related to electric and magnetic fields Light can be thought of as both wave and particle Light as a wave: Wavelength: distance between adjacent crests/troughs 15 Frequency: # of troughs/crests that pass through a point each second (measured in Hertz [Hz]=1/sec) Speed: how fast a crest moves forward (measured in m/s) Speed of wave=wavelength*frequency Speed of light: c=3*10^8 m/s Longer wavelength means lower frequency (inverse relationship) Light as particle: Can also think of light as a beam of particles (photons) Each photon has welldefined energy Energy (E) of each photon is proportional to its frequency (v) E=hv (h is constant) Proposed by Albert Einstein Colors of light: Mix of different colors (frequencies) Sorting out colors creates a spectrum—uses a prism Matter and Spectra Matter: made of atoms Suggested by Greek philosopher Demoritus (460370 BCE) Individual, indivisible atoms Atoms known to be divisible now Atoms: all matter we are familiar with Nucleus: contains the protons and neutrons Cloud of electrons 16 Losing atoms causes ionization Quantum mechanics: cannot tell where electron is in cloud—they travel too fast and create cloud Isotopes: same atoms, different number of neutrons and atomic mass; same # of protons Light and Matter: Light moves straight until it hits something Reflects: specific direction change; comes off at same angle (like a mirror) Scatters: random direction; all different angles (like snow) Snow scatters all wavelengths Colored items (green tree) reflect only that color (green) All other wavelengths absorbed Light transmitted through window 3 types of spectra: Continuous: produced by hot and dense body From the form of spectrum we can infer the temperature of hot body All wavelengths represented (all colors) Emission: produced by hot and dilute gas From emission lines we can infer chemical composition of the gas Absorption: cold and dilute gas in front of hot and dense body Can infer the chemical composition of dilute gas and temp of hot body Understanding Spectra: Continuous (Thermal) Spectrum (Blackbody spectrum) Like an iron firepoker—as it gets hotter it gets redder and glows Hotter objects emit more radiation per unit surface area at every wavelength Peak further closer to violet is hotter on graph (shorter wavelength=increased E) 17 Understanding Emission and Absorption Spectra: Atoms: energy “slots” Energy for atom can only have specific values # of protons determines element Pattern of energy levels is exclusive of each element Energy always conserved Electrons jumping to lower energy level (excited state) gives off light Absorption of photon causes electron to jump to higher energy level Photon needs enough energy to equal higher energy level or it will pass through atom The Sun Radius: 108x earth’s Know this due to angular size (parallax) Mass: 333,000x earth rd Know this due to Newton’s version of Keplar’s 3 law Composition: all gases Know because of sun’s spectrum 98% H and He, 2% other elements Surface temp: 10,000 F Know because of spectrum Sunspots darker because they are cooler than their surroundings (spectra) 18 Age: about 5 billion years Know because we know the age of solar system by dating meteorites using radioactive element Life expectancy: about 10 billion years (calculations) Structure: Energy source is at its core Photosphere: sun’s visible surface Convection zone below photosphere Keeping Balance: In order to shine steadily, outward pressure in sun must balance inward pull of gravity To keep pressure steady, temp must be constant To keep core temp constant, must be source of energy at core that replenishes energy lost by the sun Nuclear fusion: source of energy for sun; occurs in core H smashes together to form He+energy 4HHe (atomic mass=4) + Energy At higher temp, atoms are ionized H nuclei have enough speed to avoid electrical repulsion Collide and fuse into heavier nuclei Life of the Sun sun made of plasma (ionized gas) Solar Activity: Sunspots—colder than surroundings Magnetic fields prevent the surrounding hot plasma from entering sunspot region Solar flares—magnetic fields “snap” and reconnect, releasing huge amounts of energy Released energy leads to dramatic solar storms 19 Include xrays, gamma rays, and highly energetic electrons and protons Around earth, solar flares may: Damage satellites Interfere with communications Knock out power grid temporarily Hazard to astronauts Solar Patterns: Number of sunspots on sun rises and falls Cycle of 11 years Some suggestions of a connection between solar activity and weather on earth Nuclear Fusion: Electric charge conserved—four protons mash to produce He (2 protons and 2 neutrons) neutrons, releasing two positrons and neutrinos Mass Density: Mass of proton is 938 MeV Positron= 0.5 MeV Neutrino negligible Helium nucleus 3728 MeV Final mass is less than initial mass During nuclear fusion, mass is converted into energy, carried away by photons (light) and neutrinos Mass and energy are two manifestations of the same thing—can be converted into each other (E=mc^2) Charge conservation: a proton is converted into a neutron, a positron (and a neutrino) Energy conservation: mass is converted into light (gamma rays) Sun’s life expectancy= about 10 billion years Life of the Sun: 1.) Sun began its life fusing H into He 2.) After 10 billion years, H at the sun’s core will be exhausted 20 Core of sun is now made of inert helium 3.) The pressure at the core diminishes—core contracts by the crush of gravity 4.) The temperature increases again and fusion begins at a H shell surrounding the He core 5.) The additional pressure causes the outer shell of the star to expand into a red giant Radius is 100 times the solar radius 6.) As more H gets converted into He, the pressure at the core increases 7.) He fusion begins into carbon 8.) When the core He is depleted, the sun will expand even more due to He burning in a shell surrounding the carbon core 9.) The sun will eject its outer layers, leaving behind an inert C core 10.) The outer layers will form a planetary nebula
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