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Phases of the Moon - PowerPoint PPT Presentation

Phases of the Moon. • Half of the moon is always illuminated. • Half of the moon is always illuminated. • We see all, none, or some of that illumination. The same side of the moon always faces the Earth. The same side of the moon always faces the Earth.

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PowerPoint Slideshow about 'Phases of the Moon' - lane

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Presentation Transcript

Half of the moon is always illuminated

Half of the moon is always illuminated

• We see all, none, or some of that illumination

Time for one

rotation

(axis)

Time for one

orbit

(Earth)

=

Half of the moon is always illuminated

• We see all, none, or some of that illumination

Half of the moon is always illuminated

- But it’s not always the same half!

• We see all, none, or some of that illumination

C

4π2

___

________

a3

p2 =

p2 =

MEarth

G(MEarth)

p: period (time for Moon to go around Earth)

a: Moon-Earth distance

Take home #1:

If M becomes 0.5M,

what is the new value of p?

p2 = a3

p: period in Earth years

for one orbit around the Sun

a: distance in AU

from the planet to the Sun

4π2

________

a3

p2 =

G(M1+M2)

G = gravitational constant = 6.67 x 10-11 m3/kg/s2

MSun = 1.99 x 1030 kg

MPlanet << MSun

4π2

________

a3

p2 =

G(MSun)

4π2

________

seconds  years

= 1

G(MSun)

meters  AU

GM1M2

_______

F =

d2

F = force that the Moon feels as it orbits

the Earth

M1= Earth’s mass

M2 = Moon’s mass

d = distance between Earth and Moon

If d stays the same, what happens to F

if Earth’s mass decreases?

4π2

________

a3

p2 =

G(M1+M2)

G = gravitational constant = 1.475 x 10-34 AU3/kg/day2

MEarth = 5.97 x 1024 kg

MMoon = 7.36 x 1022 kg

p = period in days of the Moon’s orbit around Earth

a = distance in AU between Moon and Earth

1 AU

_____________

400,000km x

a =

= .002667 AU

150,000,000km