1. Celestial Navigation Celestial Motion 1

2. General Organization Original “celestial sphere” model devised by the Greeks is still used –Greeks saw the Earth as the center of the universe Normal longitude and latitude lines are projected outward on to the celestial sphere

3. General Organization Two systems of positioning exist Altitude/Azimuth (Alt/Az) –Known as Horizonal System –Position dependent –Position of an object will change depending on position on Earth Declination/Right Ascension (Dec/RA) –Known as Equatorial System –Universal –Coordinates of object does not change with location on Earth

4. Horizonal System The simpler to use but less scientific system Altitude is determined by degrees off of the horizon (0 o -90 o ) Azimuth is a compass direction (0 o -359 o ) Coordinates will be different depending upon vantage point (hence less scientific) –Very useful when using standard star charts

5. Horizonal System Using the Altitude/Azimuth system, a star’s coordinates is determined by measuring the height in the sky along with a normal compass direction.

6. Equatorial System Latitude denotes distance above or below the equator –Declination denotes distance from north or south celestial pole Longitude denotes distance from prime meridian –Right Ascension denotes distance from celestial “meridian” Celestial “prime meridian” is drawn through the intersection point of the celestial equator and the ecliptic

7. Equatorial System Dec/RA system takes into account the 23.5 o tilt of the planet and makes the celestial equator in line with the planet’s (as opposed to horizon) By setting the celestial sky in line with the planet’s, a non-changing set of coordinates can be devised

8. Equatorial System Declination (Dec.) –Measured the same as latitude –Degrees, minutes, seconds north or south of the celestial equator –If declination is south of the celestial equator, (-) declination is shown Example:Polaris +89 o (Ursa Minor) –Polaris is located at the celestial North Pole Example:Rigel -8 o 15'(Orion)

9. Equatorial System Right Ascension (RA) –Celestial equivalent of longitude –Is not measured in degree, etc. Measured in hours, minutes, seconds Measured eastward –Uses 24 hour system 24 hr = 365 o 12 hr = 180 o –Each hour of ascension = 15 o –Examples Polaris:1hr, 49 min.(Ursa Minor) Rigel:5 hr, 12 min.(Orion)

10. Equatorial System

12. Observing the Night Sky Earth rotates from West to East (counter clockwise in northern hemisphere) Apparent movement of stars are different depending upon latitude on Earth Entire sky rotates around Polaris –If at the equator, a viewer can see ALL stars in the sky –If at the poles, starfield never changes

13. Observing the Night Sky Earth lies in a plane of the solar system with all of the other planets –Called the ecliptic Defined as the apparent path of the sun Since the sun, moon and planets all travel along this path, the zodiac constellations can be seen here –If a few zodiac constellations can be identified, confirmation of planet sightings can be reached

14. Observing the Night Sky The celestial sphere with Ecliptic indicated for comparison. The apparent discrepancy between the tilt of the Earth with respect to the plane of the solar system is what makes constellations rise and set.