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Sky coordination systems & celestial sphere

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Celestial Sphere,
Sky Coordination Systems

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Sky coordination systems & celestial sphere

  1. 1. Astronomy & Space Science Association in University of Kelaniya Astro Night 2014 Lecture 2 Coordination Systems in the Sky & Celestial Sphere Eranga Jayashantha Hon. mentd Dip in Astronomy & Astrophysics ( IOAA – China ) National Representative at Space Generation Advisory Council ( UN ) Sri Lanka national Astrophysics Olympiad Team Trainer at Institute of Physics Sri Lanka
  2. 2. Latitude and Longitude  Latitude (f) meas from equator  Longitude (l) point of reference – Greenwich UK  Units of measure:  Deg, arcmin, arcsec  O ‘ “
  3. 3. Two types of Coordination Systems are used to describe the position of an object in the Sky 1) Horizon System 2) Equator System
  4. 4. The Horizon System  Altitude (h) – angle measured from the horizon to Zenith (Z)  Azimuth – the angle measured from NE along horizon  Problem as a celestial system?
  5. 5. What is an Equator System? Based on Right Ascension & Declination
  6. 6. Celestial Sphere  Imaginary sphere where stars reside  Extension of Earth’s equator, poles  Celestial Equator  Celestial poles  Zenith & Nadir
  7. 7. • Celestial equator divides the sky into northern and southern hemispheres •Celestial poles are where the Earth’s axis of rotation would intersect the celestial sphere • Polaris is less than 1° away from the north celestial pole, which is why it is called the North Star or the Pole Star. •Point in the sky directly overhead an observer anywhere on Earth is called that observer’s zenith. – Nadir is directly opposite the zenith
  8. 8. Declination & Right Ascension  Declination = Latitude  Celestial Equator d = 0  Latitude, NCP elevation  Units: deg, arcmin, ‘’  The Celestial Meridian  Great circle going through zenith & NCP  Right Ascension = Longitude  Units: hh:mm:ss  360o = 24 hr (1 hr = 15o)  Where to start RA?
  9. 9. How the Equatorial Coordinates are changed over a long time?  Due to two main reasons 1) Precision of Equinoxes 2) Lunar orbit is getting far from Earth by ~3cm per year ( Earth’s rotational angle is getting changed )
  10. 10. Thank you

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