Phases of the Moon Half of the moon

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. . . 2 4π ____ 3 2 a p = G(MEarth) p 2 C ___ = MEarth p: period (time for Moon to go around Earth) a: Moon-Earth distance Take home #1: If M becomes 0. 5 M, 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. . .

2 p = 3 a p: period in Earth years for one orbit around the Sun a: distance in AU from the planet to the Sun

p 2 2 4π ____ 3 a = G(M 1+M 2) G = gravitational constant = 6. 67 x 10 -11 m 3/kg/s 2 MSun = 1. 99 x 1030 kg MPlanet << MSun 2 4π ____ 3 2 a p = G(MSun) seconds years meters AU 2 4π ____ = 1 G(MSun)

GM 1 M 2 _______ F= d 2 F = force that the Moon feels as it orbits the Earth M 1= Earth’s mass M 2 = Moon’s mass d = distance between Earth and Moon If d stays the same, what happens to F if Earth’s mass decreases?

p 2 2 4π ____ 3 a = G(M 1+M 2) G = gravitational constant = 1. 475 x 10 -34 AU 3/kg/day 2 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 _______ a = 400, 000 km x =. 002667 AU 150, 000 km