1. A scientific model

2.  Why do we use the model of the celestial sphere when studying the night sky, even though it does not accurately represent three-dimensional space?  How can you locate constellations and other sky objects using the coordinate system of the celestial sphere?  Why are different constellations visible in the sky at different times of the year or from different places on Earth?

3.  An imaginary sphere used to help locate celestial objects.  The Earth is at the center and the celestial bodies (stars, planets, galaxies, etc) are “painted on” the surface of the sphere  It is considered a scientific model

4.  Horizon – the visual boundary between Earth and the sky (with cardinal points N, S, E, and W)  Zenith - Point on the celestial sphere directly overhead  Nadir -Point on the celestial sphere directly underneath the observer’s feet  Celestial equator - a projection of Earth’s equator onto the celestial sphere, always crosses the horizon directly East and West  Celestial Poles projection of Earth’s north and south poles onto the celestial sphere

5. From geographic latitude l you will see the celestial north pole ( l) degrees above the Northern horizon l Locating the Celestial North Pole and Celestial Equator in your sky zenith

6. The Celestial South Pole isn’t visible from the Northern Hemisphere. Celestial Equator is visible in the sky 90 o south of the CNP Horizon Looking North Celestial North Pole 40.7 0 Example: New York City: l ≈ 40.7º Polaris Zenith (90 o above horizon) Same as latitude ( l )

7.  Latitude: (parallels) marks locations north and south of the equator  Longitude: (meridians) marks locations east and west of the Prime Meridian

8.  Declination (Dec): imaginary lines on the celestial sphere that show positions north and south of the celestial equator  +60 o is north and -60 o is south  Similar to latitude lines on the Earth  0 o declination is at the celestial equator

9.  Similar to longitude on Earth  Usually measured from 0 – 24 hours.  Right ascension is a unit of angle  As you face north, the stars will appear to rise (ascend) from the east (your right).  The celestial meridian (0 hour) is a semicircle connecting the celestial poles and passing through the vernal equinox on the celestial equator Right Ascension (RA): The E-W position of a celestial body

10.  Constellations, stars, galaxies, etc. can be given an “address” in the sky using RA and Dec.  Degrees of Declination (Dec) can be divided into 60 arcminutes and each minute of arc can be divided into 60 arcseconds.  Hours of Right Ascension (RA) can be divided into minutes and seconds as well.  So, the specific “address” for the star Antares is  Dec: -26 o 25’55”  RA: 16 h 29 m 30 s

11. The Sun’s apparent path on the sky is called the Ecliptic. OR The Ecliptic is the projection of Earth’s orbit onto the celestial sphere.

12.  http://www.youtube.com/watch?v=2-TtcfmbrkI http://www.youtube.com/watch?v=2-TtcfmbrkI

13.  Why do we use the model of the celestial sphere when studying the night sky, even though it does not accurately represent three-dimensional space?  How can you locate constellations and other sky objects using the coordinate system of the celestial sphere?  Why are different constellations visible in the sky at different times of the year or from different places on Earth?