Astronomy 115 - Study Guide for midterm 1
Astronomy 115 - Study Guide for midterm 1 ASTR 115
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This 8 page Study Guide was uploaded by Eva Malek on Saturday February 21, 2015. The Study Guide belongs to ASTR 115 at San Francisco State University taught by Julio Magalhaes in Spring2015. Since its upload, it has received 885 views. For similar materials see Intro to Astronomy in Astronomy at San Francisco State University.
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Date Created: 02/21/15
ASTR 115 Introduction to Astronomy Study Guide for first midterm Chapter 1 2 and 3 1 OUR PLACE IN THE UNIVERSE Our Astronomical Address Sol 3 Earth solar system Milky Way Galaxy Local Group of Galaxies Local Supercluster Universe Stars glowing balls of gas that generate heat and light Asteroid small rocky orbits stars Comet small icy orbits stars Solar system a star and all the objects that orbit it Galaxy great islands of stars held together by gravity and orbiting a common center Nebula Interstellar cloud of gas and dust Seven wondering objects Sun Moon Mars Iupiter Venus Saturn names of the 7 days of the week Daily Motion apparent motion of starts around earth Constellation groups of Stars specific areas in the sky 2 THE SCALE OF THE UNIVERSE l Planetary Size Scales l Earth Diameter 13000 Km Iupiter 11 Earths 143000 Km l Stellar Size Scales our Sun l Sun s Diameter 10 Iupiters 110 Earths l The Astronomical Unit AU l Interplanetary distance Average distance between earth and sun 1 AU 150 million km 150 x 106 Km Light Travel Time a distance unit l Speed oflight 300000 kmsecond Light travel 1AU in 8 minutes Light from Pluto takes 5 hours to arrive to earth 5 light years distance Light year 95 x 1012 Km l Distance between Stars l Alpha Centauri the closest star distance 42 light years l Size of Milky Way Galaxy l 100000 light years across Sun is 1 of 100 billion stars l Distance Between Galaxies l 100 billion galaxies Andromeda Galaxy closets galaxy 22 million light years Furthest edge of the Universe 14 billion light years 3 THE COSMIC CALENDAR 9 14 billion years of history of the universe compressed into 1 year Most important events The big Ban Universe begins to expand Formation of Milky Way Formation of Solar System and Earth Origin of Life around September Diversification of Life Human Understanding of the Cosmos 4 SPACESHIP EARTH Rotation Spinning around an axis Speed depends on latitude Revolution Motion around another object 9 Earth revolves around Sun in 1 year at 107000 km hour Expansion Galaxies are moving away from each other with time THE CELESTIAL SPHERE A mental and physical device for representing constellations The Earth is on the center and stars are all quotpaintedquot in the celestial sphere North Celestial Pole Horizon Zemth Altitude Angle South Celestial Pole Constellation o A region in the sky 0 88 fill our entire sky 0 Stars are at different distances and not related 0 Circumpolar Stars constellations above the horizon Zenith The point directly overhead Horizon All points 90 degrees away from Zenith Meridian Line passing through Zenith and connecting N and S points Angles in Local Sky 0 Fist10 degrees 0 Finger1 degree Angle Size physical size X 360 degrees 2pi X distance Angular Measurements 1 degree 60 arcminutes 1 60quot arcseconds Earth rotates west to east 9 appear to circle from 5 Determining Your Latitude From the Nigh Sky Latitude Horizontal lines Longitude Vertical lines When North Celestial Pole NCP is at your Zenith o Altitude 90 degrees 0 You only see stars from northern hemisphere of CP 0 Stars neither rise nor set The altitude angle of NCP at you location your latitude SUN 0 Drifts eastward with respect to stars Ecliptic sun paths on celestial sphere 0 Seasonal drift of Sunquot drifts Eastward 1 degree per day due to the Earth s orbital motion around the sun 0 o Sidereal day time it takes Earth to rotate 360923h 56 min 0 Solar Day time it takes from high noonquot to high noonquot924h o Rotates 1 degree every 4 minutes 6 Cause of the seasons 9 Earths Axial Tilt Rotation axis is tilted by 235 degrees with respect to axis of Earth s orbit Changing angle to ground spreads or concentrates sunlight hitting ground In northern Hemisphere 0 Spring Equinox Mar 21 sun is directly north crossing celestial equator heading north 0 Summer Solstice June 2 1 sun riches highest point in sky during the year 0 Fall Equinox Sep 21 Sun crosses equator heading south 0 Winter Solstice Dec 2 1 Sun reaches lowest point on sky at noon 9 Dates reversed for Southern Hemisphere 7 Slowly Changing Direction of Earth s Spin axis Precession 9Low drift of direction of Earth s spin axis 9 Produced by moon and sun exerting a gravitational pull on earth s midriff bulgequot 9 Period 26000 years 9 Does not affect axial tilt of earth 9 Slightly shifts location of seasons Milankovitch Cycle 9Gravitational tugs on earth 9Produces small changes in earth s climate orbit tilt ice ages interglacial periods 2 The Moon Drifts eastward moon orbit is elliptical Lunar Phases First quarter new moon third quarter full 9Caused by changing angle between earth sun and moon Crescent Moon less than half Gibbous Moon more the half less than full moon Waxing growing Waning decreasing First quarter Waxing gibbous Waxing crescent Waning crescent Waning gibbous Third quarter 3 Eclipses Causes Sun and moon have same angular size 05 degrees They travel across celestial sphere on nearby paths Nodes Where Moon s orbit crosses the ecliptic Lunar Eclipse When full moon occurs near a node of moon s orbit Moon enters Earth s shadows Solar Eclipse When new moon occurs at node of Moons orbit Earth is in Moon s shadow 8 The Science of Astronomy Modern Science Traces its roots to ancient Greece 0 First people known to make models of nature 0 Sought to explain patterns in nature without resorting the myth or the supernatural Key principles of Modern Science Understanding of natural phenomena gt Gather evidence observation data gt Develop ideas of how nature works models hypothesis gt Test the ideas gt Apply principles of logical thinking The Scientific Method Question Hypothesis Prediction Testing hypothesis by gathering more data If hypothesis survives extend testing Theory Must be falsifiable Puzzling Motion of the wondering stars planets 9planets known in Ancient Times 0 Mercury always close to the sun in the sky 0 Venus very bright when visible morning or evening star 0 Iupiter very bright top of the sky 0 Saturn Modernly bright above Mars in sky Westward daily motion of celestial sky l Prograde Motion 9Sun and moon 9Eastward motion relative to the stars l Apparent Retrograde Motion l 9Planets relative to the stars 9Planets usually go right eastward Prograde But sometimes they go westward Retrograde THE GEOCENTRIC MODEL early explorations of planetary motion 0 Earth the center of the universe 0 Orbits are perfect circles o Epicycles circles upon circles to explain retrograde motion Strengths of this model Explained phases of the moon Predicts position of sun and moon OK job prediction of Mars Jupiter and Saturn position Weaknesses ofthis model Does not explain retrograde motion correctly Didn t explain why Venus and Mars stay close to the Sun Didn t explain why planets are brighter when they are opposite to the sun The Heliocentric Model Revolutionary idea Sun is at the center not earth Earth and planets revolve around the run Figures out order of planets distances Retrograde motion occurs when we pass by a planet in its orbit OOOOO Strengths of the model Explains phases of the moon Predicts positions of sun and moon OK job prediction position of planets Easily explains apparent retrograde motion Allows layout of solar system to be understood Conceptually simpler Weaknesses ofthe model Not that accurate predicting planetary position because it still used perfect circles No stellar parallax observed 9 angular shift of an object in foreground when viewing from different location Refinement of Heliocentric Model Kepler s Three Laws of Planetary Motion Better measurement by Tycho Brahe Better data Complied most accurate naked eye measurements of planetary position Hired man who discovered truth about planetary orbits and motions Johannes Kepler 9Finds that elliptic orbits match the data much better l Law 1 The Law of Ellipses l Planets orbits are ellipses with the sun at on focus l Law 2 Law of Equal Areas l The area swept out by a planet in a given time is always equal l Law 3 The Law of Periods and Distance The orbit periods squared are proportional to the cubes of the semi major areas
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