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Astronomy & Astrophysics
Clifford Orwin

Lecture 1 Chapter 1 1 AU (astronomical unite): average distance between Earth and sun 150 mil km Mercury: 0.4 AU Jupiter: 5 AU Neptune: 30 AU Distance light travels in a year: 300 000 kms 1 light year = 63 000 AU or 10 trillion km Earth -> Sun = 8 light minutes Nearest star = 4 light years Galaxy: island of stars (billions) in space held together by gravity nearest galaxy: Andromeda = 2.5 mil light years away Universe: sumtotal of all matter and energy, that is, everything within and between galaxies Star: glowing ball of gas, generates heat and light through nuclear fusion Planet: orbits a star, shines by reflecting light rocky, icey, gaseous Moons: orbits a planet Comet: small, icy object that orbits a star has a tail Solar system: star and all material orbiting around it Nebula: interstellar cloud of gas or dust Galaxy: large island of stars held together by gravity, orbit around a common centre Equator: 1670 kmh rotating speed Tropics: 1275 kmh Spin axis tilted by 23.5 degrees (pointing to polaris) -tilted in direction it orbits (counter clockwise) -1 AU (150 mil km) Sun moves relative to other stars speeds of 70 000 kmh -stars take 230 mil years to orbit galaxy 1658: Bishop James Ussher Sunday, October 23, 4004 BC -Bible = not literal -radioactivity discovered in 1900 -1920: Earth thought to be 4 billion years old Hubble: -universe expanding, galaxies moving away fromus -farther away something is, faster away it moves v=Hsub0d -13.7 bil years old amount of hydrogen burned by oldest stars -Hubble telescope observe galaxies 12.5 bil light years away = what they looked like 12.5 bil years ago -> can see what universe looked like when it was 1 bil years old observable universe: portion of the entire universe we can potentially observe 14 billion light years away Big Bang produces H, He heavy elements in stars create starsplanets -atoms made in stars, only simple atoms were in Big Bang, complex atoms created in stars -stars die, expelled to formnew starsplanets nuclear fusion: process in which lightweight atomic nuclei smash together and stick to make heavier nuclei Lecture 2 Chapter 4 ,8L.3,9:70412,9907OO9KL3J8,702,0:541,9428OL99O05,79L.O089K,924;0,74:3L350709:,O motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into 430,349K07 Feynman Solid: atomsmolecules are held tightly in place Liquid: atomsmolecules remain together but move relatively easily Gas: atomsmolecules move unconstrained Plasma: free electrons move among positively charged ions atoms become increasingly ionized -elegance, simplicity = beauty in science (explaining many things with one basic idea) -beautiful things are not necessarily true -total amount of energy was created at the moment of the creation of the Universe changes in Universe are just energy changing into another form (First Law of Thermodynamics). -energy can be converted into kinetic, potential, thermal, nuclear, geothermal, wind, sound, solar energy PERFECTLY www.notesolution.com -energy measured in joules -three basic types of energy: kinetic (motion), potential (stored), radiative (light) -thermal energy: total kinetic energy of many particles (depends on temperature and density) Law of Conservation of Energy: energy cannot be created or destroyed, only transformitself fromone form into another total energy in universe remains constant Gravitational Potential Energy: how far a mass can fall as a result of gravity (as h decreases, vincreases) -temperature is a measure of the average kinetic energy of the particles L1,OO5,79L.O08Z0LJK9K08,20L98 M:89,20,8:70419K0,;07,J085009K07024;L3J -the more atoms there are (even if two things are the same temperature), the more heat there is -atoms are divisible (e.g., plasma) Lecture 3 Chapter 4 speed=distancetime (how far an object will travel in certain time) velocity=speed with an associated direction acceleration: how velocity changes over time -if speed is constant but direction of velocity changes, acceleration changes momentum=mass x velocity -momentumcan only be changed when a force is applied to an object (where force=mass x acceleration) mass=total amount of matter weight=mass times acceleration of gravity (force on the scale) Law of inertia: everything in the universe wants to move in a straight line at a constant velocity -velocity of zero means that if something is stopped ,it wants to stay stopped -when you see a changing velocity, something is being acted on by a force Angular momentum: present when object rotates or moves on curved path -force that changes angular momentum= torque -acceleraction by gravity: for each second an object falls (ignore air resistance) it increases in speed by 9.81ms If gravity is so weak, why does it seemto control the Universe? Because gravity only pulls, and never pushes. So as you add more stuff, you get more gravity. It never cancels out. .05O078O,Z8 5O,309824;0L30OOL59L.,O47-L98 2489.4209824;0L35,7,-4OL.47-L98 2. They sweep out equal areas in equal times 3. Period squared is distance cubed -when you are nearer to the sun, you move more quickly -the more stuff there is, the more gravity there is (fromthe stuff) -further away you are from stuff, the less gravity you feel -the smaller something is, the less gravity it has, and the farther away from the sun you are, the less gravity there is and things rotate more slowly -weightlessness is due to falling and not hitting anything still subjected to gravity, still have mass Newton: brought together the heavens and earth, saying physical laws that applied on earth also apply in space = astrophysics 0Z9438,Z84149L43 1. Objects move at a constant velocity or stay at rest until an outside force is acted upon the object 2. Force = mass x acceleration 3. For any force, there is always an equal and opposite force Law of Conservation of Momentum: total momentum of a systemdoes not change unless an eternal force is applied to one of the objects in the system Law of Conservation of Angular Momentum: in the absence of external torque, the total angular momentumof a system must remain constant -angular momentum= mass x velocity x radius fromsun Rotational Angular Momentum: as r decreases, the v must increase to compensate -earth loses some r.a.m. because tides create friction which slow orbit ABSOLUTELY NO ORBIT IS CIRCULAR, THEY ARE ALL ELIPTICAL! -0OOL5808,7043O147-4:347-L98 ,347-L9ZK070,34-M0.9.L7.O08,349K077050,90O4;079L20 www.notesolution.com&3-4:347-L98 a path 9K,9-7L3J8,34-M0.9.O48094,349K0743O43.014OO4Z,5,7,-4OL.47 hyperbolic route -objects orbit their Common Centre of Mass (the point at which both two objects would balance of connected) -sun: its mass is so large that this point still lies within the star itself -:8L3J0Z9438078L4341.0O50789KL7O,ZZ0.,320,8:709K02,8841,5O,309L1L947-L98, significantly larger object this is the primary method we use to calculate the mass of other planets Orbital Energy = Gravitation Pot. Energy + Kinetic Energy -orbits cannot change spontaneously through Gravitational Encounters where one object passes closely to another and thus can feel each others gravitational effects -gravitational encounters can be used to speed up satellites as they travel through space, as it gains orbital energy from the planet which it passes -atmospheric drag only affects low orbit satellites around earth (few hundred Km in altitude) -transforms its Orbital Energy into Thermal Energy which is evidenced by satellites burning up as they plummet towards the earth during reentry 8.,500O4.L9%K0;0O4.L9706:L7094O0,;047-L941,5O,30901L30-9K014OO4ZL3J -M0.982,88 does not affect Vescape) 2 G m K V escape 490,79K80N2 8 40,000 Kmhr) r Universal Law of Gravitation: -force is directionally proportional to the mass of both objects -strength of force decreases by square of the distance -if one would double the distance between two objects, force decreases by a factor of four (2^2=4) Lecture 4 Chapter 2.1-2.2 Constellations: a region of the sky with well-defined borders, not just patterns of stars (we use the stars to find the constellations) -88 constellations set by International Astronomical Union in 1928 The Celestial Sphere: ancient Greeks believed that all stars were the same distance from earth and lied on a .0O089L,O85K070 not true, we lack depth perceptions bc stars are so far away so they appear to be close together north celestial pole: point directly over ,79K8479K!4O0 84:9K.0O089L,O54O054L39L70.9O4;07,79K8$4:9K!4O0 .0O089L,O06:,947574M0.9L4341,79K806:,947L39485,.0 2,N08,.425O090.L7.O0,74:3 celestial sphere ecliptic: path the Sun follows as it appears to circle around celestial sphere once each year .748808.0O089L,O06:,947,9 0J700,3JO0- .9K,9L8,79K89LO9 Milky Way: circles around celestial sphere so you can only see part of it at a time -formed by interstellar gas and dust of the Milky Way Galaxy (we are halfway fromthe center so we can see it) -dark lanes appear in it when strong clouds block the light of the stars behind it -kept much of the galaxy hidden until technology conqured it The Local Sky: the half of the celestial sphere you can see at a time (other half hidden by ground) -meridian: imaginary half circle stretching fromhorizon due south through zenith to the horizon due north -can pinpoint position of object in local sky by knowing direction along horizon (azimuth degrees clockwise from due north) and altitude above horizon Angular Sizes and Distances: we cannot judge true sizes of objects we see, only angular sizes angular size of an object: the angle it appears to span in your field of view does not tell by itself 4-M0.98true size because it also depends on distance angular distance between a pair of objects: angle that appears to separate them 1 degree = 60 arcminutes 1 arcminute=60 arcseconds www.notesolution.com
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