# Phases of the Moon - PowerPoint PPT Presentation

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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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Phases of the Moon

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#### Presentation Transcript

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.

The same side of the moon always faces the Earth.

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

A few notes for the take home...

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?

A few notes for the in-lab...

A few notes for the in-lab...

A few notes for the in-lab...

A few notes for the in-lab...

A few notes for the in-lab...

A few notes for the in-lab...

A few notes for the in-lab...

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