1. EARTH IN SPACE

2. A reminder about earth  The earth is almost a sphere  We locate points on the sphere with 3 coordinates – Longitude (180º W -- 180º E) – Latitude (90º S -- 90º N) – Altitude (m above/below sea level)  These are referred to as Terrestrial Coordinates

3. Finding Polaris: The North Star  Polaris is nature’s compass  Draw a line straight from Polaris to the horizon with your finger and you will be pointing toward geographic north

4. Position of Polaris  Polaris stays in the same spot throughout the night.  We say it has the same altitude and azimuth throughout the night.  Altitude and azimuth are the local coordinates

5. Celestial Coordinates  Declination and right ascension:.  Declination is the same as latitude  Right ascension is the same as longitude.

6. CELESTIAL MOTION  Every celestial object changes position over time (it is in motion).  This motion is not random.  The movement is from East to West.  All move at the same rate.  Celestial objects appear to follow a circular path at a constant rate of 15 degrees per hour (or one complete circle every day).  This motion is called the apparent daily motion

7. Celestial Sphere

8. CELESTIAL SPHERE  An imaginary sphere surrounding the Earth.   on which all celestial objects would appear.   Celestial object = any object in the sky that appears to rise in the east and set in the west. Examples: moon, sun, stars, planets.  Celestial poles are directly over Earth’s poles  Celestial equator lies over Earth’s equator  Zenith is a point directly above the observer  Celestial meridian is the circle that runs through the celestial poles and the zenith.  As Earth rotates from west to east, all objects in the sky appear to move from east to west, revolving around the north celestial pole

9. What About Earth’s Motions? Two Motions: Rotation: Spinning of Earth on it’s axis Revolution: Motion (orbit) or Earth around the Sun. How do we know Earth rotates?  Day/Night  Coriolis Effect  Foucault Pendulum

11. Rate of Rotation  How many degrees are in a circle? 360  How many hours are in a day? 24  If you divide the number of degrees by the number of hours, you get the degrees the Earth rotates per hour!  The Earth rotates 15°/hour

12. Path of a Star   Stars that are overhead: follow the same path as the sun (rise in the east and set in the west).   Stars that are close to Polaris: (Celestial North Pole) – appear to move in circles around Polaris (circumpolar stars) – They are in the Northern sky.   Stars that are in the Southern Sky: Rise and set near the horizon because they are mainly visible in the Southern hemisphere.

13. Earth Rotation = Sky Rotation Polaris - The North Star Circumpolar Star *image taken from http://apod.nasa.gov/apod/ap051220.html Noncircumpolar Star Horizon - where the sky meets the earth

17. Constellations  Apparent pattern that people use to mark the position of the stars  88 Constellations  The sky is divided into these 88 regions, each associated with a constellation  Constellations change with the season