1. Phys141 Principles of Physical Science Chapter 17 The Moon Instructor: Li Ma Office: NBC 126 Phone: (713) 313-7028 Email: malx@tsu.edumalx@tsu.edu Webpage: http://itscience.tsu.edu/ma Department of Computer Science & Physics Texas Southern University, Houston Nov. 22, 2004

2. Topics To Be Discussed General Features Lunar Motions Phases of the Moon Skip –§17.2 Composition and History of the Moon –§17.5 Eclipses –§17.6 Ocean Tides

3. About the Moon The Moon is related to the time measurement –The length of our present month is based on the motion and phases of the Moon The Moon appears as the second-brightest object in the sky because it is very close to us –The average distance between the Earth and the Moon is 384,000 km

4. General Features of the Moon The Moon revolves around the Earth in approximately 29.5 solar days Because it rotates at the same rate as it revolves around the Earth, we see only one side of the Moon So on the Moon –You can always see the Earth if you stand on the side facing the Earth –The Sun appears to rise and set once every 29.5 days

5. General Features of the Moon (cont) The nearly spherical Moon has a diameter of 3476 km, slightly greater than one-fourth of the Earth’s diameter The surface gravity of the Moon is only one- sixth that of the Earth The Moon does not possess a detectible magnetic field Its phases and the appearance of its surface are the Moon’s predominant features

6. General Features of the Moon (cont) The surface of the Moon is marked with craters, basins, plains, rays, rills, mountain ranges, and faults These features vary in size, shape, and structure The most outstanding of them are the craters that are clearly visible to an Earth’s observer with even a telescope

7. Lunar Motions The Moon revolves eastward around the Earth in an elliptical orbit There are two different months –The period of the Moon with respect to the Sun is a little over 29.5 days – synodic month, or the month of the phases –The period of the Moon with respect to a star other than the Sun is approximately 27.33 days – sidereal month, the actual time it takes for the Moon to revolve 360°

8. Lunar Motions (cont) To an observer on the Earth, the Moon appears to rise in the east and set in the west each day. This apparent motion of the Moon is due to the Earth’s completing one revolution each day

9. Phases of the Moon The most outstanding feature is the periodic change in its appearance –A new moon: the illuminated half is all hidden –A full moon: the illuminated half is all presented –A crescent moon: less than one-quarter of the Moon’s surface appears illuminated –A gibbous moon: more than one-quarter of the Moon’s surface illuminated

10. Phases of the Moon (cont) The new phase of the Moon occurs when the Earth, Sun, and Moon are in the same plane, with the Moon positioned between the Sun and Earth The Moon is in first-quarter phase when it is 90° east of the Sun When the Moon is 270° east of the Sun, it will be in the last-quarter phase

11. Phases of the Moon (cont) When the Moon is 180° east of the Sun, it will be in full phase and will appear as a full moon to the Earthbound observer The waxing phase means that the illuminated portion of the Moon is getting larger The waning phase means that the illuminated portion of the Moon is getting smaller

12. Assignment Homework Assignment –Review Questions (page 455 – 456): 2,5,6,24,28,29,32,36 –Exercises (page 457): 2 –It’s due Monday, 12/6/04 Reading Assignment –Chapter 18