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01 Celestial Sphere  Mc Neely 2010
 

01 Celestial Sphere Mc Neely 2010

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    01 Celestial Sphere  Mc Neely 2010 01 Celestial Sphere Mc Neely 2010 Presentation Transcript

    • Understanding the Starry Sky Ch. 01
    • Celestial Sphere
      • A model of the universe
      • We picture the sky as a hollow globe surrounding earth
      • All stars are positioned inside the globe facing earth
    • Celestial Sphere http://www.astro.columbia.edu/~archung/labs/fall2001/lec02_fall01.html
    • Celestial Sphere Animation
      • Animation 1.1: Celestial Sphere
    • Celestial Sphere Features
      • “ Sphere” appears to revolve around earth each day
      • Earth’s equator extended becomes celestial equator, earth’s poles (N&S) become celestial poles
      • Ecliptic is the path of the sun around the celestial sphere, requires one year for a revolution
    • Ecliptic & Celestial Sphere http://www.utm.utoronto.ca/services/gallery/img/ecliptic.gif
    • Constellations
      • 88 official
      • Many ancient, 48 Greek constellations
      • Types
        • Seasonal
        • Zodiac
        • Circumpolar
    • In order to more easily locate objects in the sky, we divide the sky into regions named after familiar patterns of stars called constellations . Ancient constellations were imaginary pictures outlined by familiar patterns of stars (stick figures). Modern astronomers divide the sky into 88 official constellations or regions of space, many of which contain the ancient star patterns.
    • Sphere image of Constellation Boundaries
    • Zodiac
      • 12 Constellations (traditional) along the ecliptic
      • Pisces, Aries, etc.
    • Circumpolar Constellations
      • North and South
      • Never setting (N), or never rising (S)
      • In north, appear to wheel eternally about Polaris, the North Star
      • Ex: Ursa Major (Big Dipper)
    • Circumpolar Stars http://www.nmm.ac.uk/upload/img/circumpolar.jpg
    • “ Star Trails”
    • N & S Circumpolar Stars http://www.mhhe.com/physsci/astronomy/fix/student/images/01f19.jpg
    • Star Maps
      • Star Maps represent portions of the celestial sphere
      • Seasonal star maps provided in your textbook (appendix)
    • Horizon Star Map http://www.drypen.net/Star_Map_3.jpg
    • Equatorial Star map http://www.starlight-theatre.ca/images/MAP-C.GIF
    • Bright Star Names
      • About 50 of the brightest stars
      • Ex : Aldebaran, Sirius
      • Mostly Arabic, some Greek & Latin
      • Bayer (1600), Greek letter names of stars
        • Ex : Alpha (  ) Tauri means brightest star in constellation Taurus
      • 26 Brightest Stars
      http://www.astro.wisc.edu/~dolan/constellations/extra/brightest.html
    • Star Magnitude (Brightness)
      • Apparent Magnitude : Brightness of a star as seen from earth
      • Traditional : Greek Hipparchus, assigned 6 categories with 1 being the brightest (first magnitude)
      • About 100x brightness difference between 1 and 6
      • To calculate magnitude differences:
      • 2.5199 (m2-m1)
    • Apparent Magnitude Scale
    • Terrestrial Coordinates http://www2.shastacollege.edu/dscollon/images/Figures,%20Diagrams%20and%20Maps.htm
    • Celestial Coordinates
      • Celestial Equator : Extension of earth’s equatorial plane into space along the celestial sphere
      • N & S Celestial Poles
      • Vernal Equinox-Sky’s “prime meridian”
      • Coordinates:
        • Declination (Dec)
        • Right Ascension (RA)
    • Celestial Globe http://www.onr.navy.mil/focus/spacesciences/observingsky/sphere1.htm
    • RA & Dec http://abyss.uoregon.edu/~js/ast122/lectures/lec02.html
    • Summary Earth Globe Celestial Sphere North Pole North Celestial Pole South Pole South Celestial Pole Equator Celestial Equator Prime Meridian Vernal Equinox Latitude Declination Longitude Right Ascension
    • Horizon System
      • Coordinate system based upon an observer’s horizon, not the celestial equator
      • Guidelines
        • Horizon-”Straight ahead”, line where earth and sky appear to meet
        • Zenith-point straight up
        • Meridian-Line “due south”, passes from north horizon through zenith to south horizon
        • Nadir-point straight down
      • Coordinates
        • Altitude
        • Azimuth
    • Horizon System Diagram http://www.yorku.ca/phall/P1070W05/L04/bea02-05.jpg
    • Altitude & Azimuth http://www.nmm.ac.uk/upload/img/altaz-star2.jpg
    • Degrees in the Sky
      • Angular Measure
        • Based on degrees of a circle = 360 º
        • Finger tip = 1 º
        • Fist = 10º
        • Outstretched hand = 20º
      • From horizon to zenith = 90 º
      • The moon and sun = 1/2 º, your finger tip will cover them (try this with the moon only)
    • Angular Measure http://www.physics.capcollege.bc.ca/stan/Angular_measure.jpg
    • Polaris & Latitude
      • The height of Polaris (North Star) in degrees above the horizon is equal to an observer’s latitude (distance above the equator)
      • Our latitude  42-degrees
      • Polaris will be about four fist-lengths above horizon
      • Useful for navigation
    • Geometric Explanation p = Location x ° = Latitude a° = Altitude of Polaris x° = a° http://homepage.mac.com/kvmagruder/images/polarislat.gif
    • Earth’s Motions
      • Rotation
      • Revolution
      • Precession
    • Earth’s Motions: Rotation, Revolution
    • Revolution
    • Earth’s Seasons
      • Sun’s Apparent Yearly Motion
        • Sun travels around ecliptic
        • About 1° per day
          • 360°/365 days  1° per day
        • Sun high in summer, low in winter
    • Seasonal Heights of Sun
    • Seasonal Sun Paths http://www.madison.k12.wi.us/planetarium/sunpath.gif
    • Seasonal Constellations SEPTEMBER MARCH
    • Earth’s Seasons http://www.learn.londonmet.ac.uk/packages/clear/visual/daylight/sun_sky/images/seasons.png
    • Earth’s Seasons
    • Seasons Animation
      • Animation 1.2: The Seasons
    • Seasons & Celestial Sphere
    • Rotation: Solar and Sidereal Day http://www.nmm.ac.uk/upload/img/sidereal-mean-day_20030415143827.gif
    • Sidereal Day  
    • Precession
      • Earth’s other motion
      • One wobble takes 26,000 years
      • Axis points in new directions during this time
      • Result, the “North Star” changes over time
        • Thuban, 3000 BC
        • Polaris, Present
        • Vega, 14,000 AD
    • Precession http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch_2a_low.html
    • Earth’s Precession http://apollo.lsc.vsc.edu/classes/met130/notes/chapter18/graphics/precession.psd.gif
    • Inconstant North Star 14,000 AD Present + North Ecliptic Pole + Ancient Egyptian polestar “ But I am as constant as the North Star…” -Shakespeare, Julius Caesar
    • http://abyss.uoregon.edu/~js/images/bz990323.gif