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Celestial sphere lrg

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Celestial sphere lrg

  1. 1. Grunt Productions 2007 Simple AstronomicalSimple Astronomical PrinciplesPrinciples (Introduction - The Celestial(Introduction - The Celestial Sphere)Sphere) A brief by Lance GrindleyA brief by Lance Grindley
  2. 2. Grunt Productions 2007 CoveringCovering  Principles of the CelestialPrinciples of the Celestial SphereSphere  Movement of HeavenlyMovement of Heavenly BodiesBodies  Simple astronomicalSimple astronomical definitionsdefinitions  Combined co-ordinateCombined co-ordinate systemsystem
  3. 3. Grunt Productions 2007 Celestial SphereCelestial Sphere  Viewed from Earth, the sky appearsViewed from Earth, the sky appears as an inverted bowl.as an inverted bowl.  The stars and other heavenlyThe stars and other heavenly bodies appear to lie on this sphere,bodies appear to lie on this sphere, irrespective of their actual distance.irrespective of their actual distance.  Radius of celestial sphere is infiniteRadius of celestial sphere is infinite so position is always described inso position is always described in angular terms.angular terms.
  4. 4. Grunt Productions 2007 Relative Motion of theRelative Motion of the Celestial SphereCelestial Sphere  Earth rotates eastwards at one revolutionEarth rotates eastwards at one revolution with respect to the sun every solar day.with respect to the sun every solar day.  Heavenly bodies appear to move westwardsHeavenly bodies appear to move westwards rising in the east and setting in the west.rising in the east and setting in the west.  Rate of rotation and apparent movement isRate of rotation and apparent movement is 360360oo divided by 24 hours = 15divided by 24 hours = 15oo per hourper hour  Angular east/west movement is measured onAngular east/west movement is measured on the equator and calledthe equator and called “hour angle”.“hour angle”.
  5. 5. Grunt Productions 2007 Southern HemisphereSouthern Hemisphere South Celestial Equator 90o - latitude
  6. 6. Grunt Productions 2007 Northern HemisphereNorthern Hemisphere North Pole Star (Polaris) latitude
  7. 7. Grunt Productions 2007 Celestial SphereCelestial Sphere North Celestial Pole South Celestial Pole Celestial Equator Parallel of Declination Celestial Meridian Celestial Meridian Hour Angle Hour Angle
  8. 8. Grunt Productions 2007 Positions onPositions on Earth/Celestial SphereEarth/Celestial Sphere  Positions are related toPositions are related to Equator and GreenwichEquator and Greenwich MeridianMeridian  Latitude and Longitude usedLatitude and Longitude used on Earth’s surfaceon Earth’s surface  Declination and GreenwichDeclination and Greenwich Hour Angle (GHA) used onHour Angle (GHA) used on Celestial SphereCelestial Sphere
  9. 9. Grunt Productions 2007 Describing PositionsDescribing Positions GHA Dec Lat Longitude
  10. 10. Grunt Productions 2007 Earth’s Solar OrbitEarth’s Solar Orbit  Earth’s axis remains stationary inEarth’s axis remains stationary in spatial terms but is notspatial terms but is not perpendicular to the plane of theperpendicular to the plane of the orbit.orbit.  Inclined axis causes the position ofInclined axis causes the position of the sun to move in relation to thethe sun to move in relation to the equator.equator.  Changing angle (declination)Changing angle (declination) creates the seasons in temperatecreates the seasons in temperate
  11. 11. Grunt Productions 2007 EclipticEcliptic First Point of Aries Ecliptic
  12. 12. Grunt Productions 2007 SeasonsSeasons Winter Solstice 22 Dec Summer Solstice 21 Jun Spring Equinox 21 Mar Autumnal Equinox 23 Sep
  13. 13. Grunt Productions 2007 Northerly DeclinationNortherly Declination N S E W P
  14. 14. Grunt Productions 2007 Southerly DeclinationSoutherly Declination N S E W P
  15. 15. Grunt Productions 2007 ConclusionsConclusions  Concept of Celestial Sphere allows usConcept of Celestial Sphere allows us to use spherical trigonometry toto use spherical trigonometry to measure relative positions and solvemeasure relative positions and solve problems.problems.  A precise time is required to predict theA precise time is required to predict the relative position of an astronomicalrelative position of an astronomical body.body.  The changing declination of the sunThe changing declination of the sun creates the seasons and changes timescreates the seasons and changes times of rise and set.of rise and set.

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