Download Chapter 17 - Department Of Computer Science

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