Coordinates in Astronomy

Coordinates in Astronomy

1. The positions of stars are measured by angles seen from earth

   • The sky appears to turn as the earth spins - so astronomers picked two fixed positions to measure from
     • THE POLE STAR: A star that doesnt seem to move because its almost directly above the North Pole
     • THE CELESTIAL EQUATOR: An imaginary plane running across the sky extending out from the earths equator
   • There are two angles used to measure positions in the sky
     • Declination - Celestial latitude measured in degrees
     • Right ascension: Celestial longitude measured in degrees or time

2. Retrograde Motion

   • All planets in the solar system orbit the sun but at different speeds, the closer to the sun the quicker the orbit
   • Often a planet seems to change direction and go the other way for a but in relation to fixed stars, making a loop in its rtack befoere carrying on as normal: THIS ONLY HAPPENS WITH OUTER PLANTS -> Mars - neptune
   • This happens because both the planet and earth are moving around the sun so we are seeing the motion relative to earth: this is when earth overtakes a planet but then earth stars to move down while mars moves horizontally making it look like its moving normally again