Phases of the Moon. Half of the moon is always illuminated.

Phases of the Moon

• 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.

Time for onerotation

(axis)

Time for oneorbit

(Earth)=


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


• We see all, none, or some of that illumination- But it’s not always the same half!

p2 = ________G(MEarth)

a34π2

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 take home...

p2 = ___MEarth

C

A few notes for the in-lab...

p2 = a3

p: period in Earth yearsfor one orbit around the Sun

a: distance in AUfrom the planet to the Sun

p2 = ________4π2

G(M1+M2)a3

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

MSun = 1.99 x 1030 kg MPlanet << MSun

p2 = ________G(MSun)

a34π2

________G(MSun)

4π2= 1seconds years

meters AU

F = _______GM1M2

d2

M1= Earth’s massM2 = Moon’s massd = distance between Earth and Moon

F = force that the Moon feels as it orbits the Earth

If d stays the same, what happens to Fif Earth’s mass decreases?

p2 = ________4π2

G(M1+M2)a3

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 Eartha = distance in AU between Moon and Earth

400,000km x _____________1 AU150,000,000km

= .002667 AUa =

Phases of the Moon. Half of the moon is always illuminated.

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