Geometric Geodesy Finals

• Astronomy


  The scientific study of the universe beyond the earth especially the observation, calculation, and theoretical interpretation of the positions, dimensions, Distribution, motion, composition, and evolution of celestial bodies and phenomena
• Prior to 1609, when the telescope was invented, the naked eye was used for measurements
• Astronomical geodesy


  A technique that uses the sun, moon, stars, and other natural objects as beacons; takes the celestial horizon coordinates of such objects as observations; and finally determines the geographical position of the station and the azimuth of one direction

  
• Celestial Sphere


  • An imaginary sphere on which are projected objects in space
  • Used to locate the positions of real and imaginary celestial objects

  
• Components of the Celestial Sphere


  • Zenith (Z)
  • Nadir (Z')
  • North Celestial Pole (P)
  • South Celestial Pole (P')
  • Polar Axis
  • Observer's Vertical
  • Observer's Meridian Circle
  • Observer's Horizon
  • Vertical Circle
  • Celestial Equator
  • Hour Circle

  
• Polaris


  The star in the center of the star field that shows essentially no movement because Earth's axis points almost directly to it

  
• The east to west daily motions of stars, planets, the Moon, and the Sun are caused by the rotation of the Earth on its axis

  
• Constellations with respect to the North Pole

  • Polaris is the last star in the tail of the constellation Ursa Minor and is located by finding the constellation of Ursa Major first
  • The two outermost stars in the cup of the "dipper" (Merak and Dubhe) are called the "pointers" because they describe a straight line that points to the North Star
  • The constellation of Cassiopeia, which looks like a big "W", is always opposite Ursa Major
  • Polaris rotates in a counter clockwise direction and makes a complete revolution in approximately every 24 hours
• Horizon System


  • Uses the observer's local horizon as the fundamental plane to define two angles: altitude and azimuth

  Primary Reference: THE HORIZON

  Secondary Reference: VERTICAL CIRCLES

  
  

  ALTITUDE – angle from the horizon to star

  AZIMUTH – the angular distance measured along the horizon

  from the observer’s meridian to the vertical circle through the

  body.

  
• Equatorial System


  • Uses two measurements: right ascension and declination Right ascension (abbreviated RA) is similar to longitude and is measured in hours, minutes and seconds eastward along the celestial equator.
  • References: Equator, Hour circles
  • parameter: Declination - angle from the equator to the star; Right Ascension - The angle taken counter clockwise along the celestial equator from the first point of Aries to the hour circle of the star.

  
• Equinox


  • Vernal Equinox: Two moments in the year when the Sun is exactly above the Equator and day and night are of equal length
  • Autumnal Equinox: Two moments in the year when the Sun is exactly above the Equator and day and night are of equal length
• Solstice


  • Summer Solstice: Two moments during the year when the path of the Sun in the sky is farthest north in the Northern Hemisphere (June 20 or 21) or farthest south in the Southern Hemisphere (December 21 or 22)
  • Winter Solstice: Two moments during the year when the path of the Sun in the sky is farthest south in the Northern Hemisphere (December 21 or 22) and farthest north in the Southern Hemisphere (June 20 or 21)
• the imaginary point that is directly above an observe

  Zenith
• the point on the celestial sphere directly below an observer

  Nadir
• the point in the sky about which all the stars seen from the

  Northern Hemisphere rotate

  North Celestial Pole
• he point in the sky about which all the stars seen from the

  Southern Hemisphere rotate

  South Celestial Pole
• an imaginary line that extends through the north and

  south geographic poles

  Polar axis
• A vertical line at the position of the observer coincides with the

  plumb line and is normal to the observer's horizon plane

  Observer’s Vertical
• a great circle on the celestial sphere that passes through the north and south points of the horizon as well as through the zenith of the observer.

  Observer’s Meridian Circle
• any great circle (similar to longitude) on the celestial sphere that passes through the celestial poles that is perpendicular to the plane of celestial equator

  Hour Circle
• great circle of celestial sphere where plane, perpendicular to the plumb line(observer's vertical) at the place of observation and passing through the center of the earth

  observer's horizon
• a circle perpendicular to the polar axis, which is the extension of the earth's equator

  celestial equator
• circle which is perpendicular to the observer's horizon and passes through the observer's zenith and any celestial body.

  vertical circle
• orbit sequence of the Polaris

  upper culmination, eastern elongation, lower culmination, western elongation. The middle is the celestial north pole
• the position of the celestial body is based on the location of the observer

  Hour Angle System
• Hour Angle system

  • LOCAL HOUR ANGLE (LHA)-The angle measured clockwise from the upper branch of the meridian of observation to the meridian of the celestial body.
  • SIDEREAL HOUR ANGLE (SHA)-The angle measured clockwise from the meridian of the First Point of Aries to the meridian of the body.
  • GREENWICH HOUR ANGLE (GHA)-The angle measured clockwise from the Greenwich meridian to meridian of the celestial body