Moon Phases Moon Phases Brainstorm • Think to yourself about the answer to this question: What causes the phases of the moon? Take out a piece of paper and quickly write down the answer. You have 2 minutes. Moon Phases • • • • Full Moon = whole moon illuminated New Moon = none of the moon is illuminated Quarter Moon = half moon illuminated Crescent = less than half of the moon illuminated • Gibbous = more than half of the moon illuminated Moon Phase Demo Earth - Moon System •Moon: a satellite of Earth •Moon has a radius of about 0.27 earth radius •Average distance from earth = 385,000 km (can fill with 30 Earth) The cause of Moon Phases? • The light that we see from the Moon is reflected light unlike the Sun, which emits its own light. The Earth and the Moon. Taken by the Galileo spacecraft (NASA/JPL). The sun provides the illumination for both the Earth and the Moon (far right of the camera’s field of view). The cause of Moon Phases? When we take pictures for the tree.. The cause of Moon Phases? • The light that we see from the Moon is reflected light unlike the Sun, which emits its own light. • The phases of the moon are caused by its orbital motion. D C B A D C A B We always see only one side of the moon... We will always see the same craters and mountains on the Moon, no matter when we look at it. Caused by Tidal Locking.. • The Moon is tidally locked to the Earth. • Its rotation period = its orbital period • Tides caused on the Moon (by the Earth) created friction that took energy from the Moon by reducing its spin. Tidal Force • We learned the gravitational force between two objects is • What if the size of objects is not negligible..? Tides • The tidal force acts on the Earth can distort the body. • Earth is rather rigid, so the distortion effects are small, but the Earth’s oceans are much more easily deformed. Tides • The ocean at point A is closer to the Moon and experiences a larger gravitational force than point B and point C. • Since the Earth rotates (the period is one day), at given place on Earth experiences high tides twice per day. Lecture Tutorial • Break up into groups of 2-3 – NO MORE THAN 3 • In your group, work through the following: – The Cause of Moon Phases (pages 79-81) – Discuss the answers – don’t be silent! • I will be roaming around if you need help… • If your group finishes, check your answers with another group & begin Predicting Moon Phases (pages 83-85).