Measuring Positions of Celestial Objects

1. Measuring Positions of Celestial Objects

3. Your Horizon

4. Horizon: plane touching the observer and perpendicular to the Zenith line. • Zenith: line running the observer straight up to the sky reaching the celestial sphere. • Celestial meridian: plan that runs from the North Pole to the South Pole passing through the Zenith.

5. The Angular Separation • Used to measure how far apart objects in the sky are • The angle between the lines originating from the eye of the observer toward two objects

7. When Objects are Too Close To Each Other 1 degree 1 arcminute = 1/60 of a degree 1 arcsecond = 1/60 of an arcminute

8. The Altitude and The Azimuth • Altitude - angle between the nearest part of the horizon and a star • Azimuth - • describes where around the 360° horizon you can find the point to look up from • angle from the north point on the horizon to the foot of the vertical circle that goes through the star.

9. The altitude is a number, between 0 and 90, representing the height of the star above the Horizon The azimuth is measured clockwise from a north base line

10. Equatorial Coordinate System • Declination (celestial latitude) • Angle N or S of celestial equator • Measured in degrees • Right ascension (celestial longitude) • Angle measured E from vernal equinox • Measured in units of time • 24 hr around the circle

11. Sun crosses the celestial equator

12. The Ecliptic The apparent path that the Sun takes among the stars.

13. Measuring Distance • Astronomical unit • 1 AU = average distance between Earth and Sun • 1 AU = 149,597,871 km • Light year • Distance light travels in 1 year • 1 light year ~ 9.6 x 1012 km • Parsec (pc) • 1 pc ~ 3.26 light years • length of the adjacent side of an imaginary right triangle in space.

14. Parsec Note: Refer to Parallax later