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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Time for one
Time for one
- But it’s not always the same half!
• We see all, none, or some of that illumination
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?
p: period in Earth years
for one orbit around the Sun
a: distance in AU
from the planet to the Sun
G = gravitational constant = 6.67 x 10-11 m3/kg/s2
MSun = 1.99 x 1030 kg
MPlanet << MSun
F = force that the Moon feels as it orbits
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?
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
= .002667 AU