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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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• 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. 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?
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
