Chapter21–OriginsofModernAstronomy.doc

Chapter 21 – Origins of Modern Astronomy Motions of the Earth-Moon System (p. 617–620) A. Introduction 1. Approximately how long does it take the moon to complete one full orbit around Earth? 2. Which way does the moon revolve around the earth? B. Phases of the Moon Definitions: The following terms define the various phases of the moon. Memorize these terms! Full Moon The moon is full when the side we see is 100% illuminated. A full moon looks like a perfect circle. New Moon The moon is new when the side we see is dark. We cannot see a new moon at all. Crescent Moon A crescent moon is shaped like a crescent; a smaller proportion of the moon is illuminated than is the case during a quarter moon. Quarter Moon The moon is called a quarter moon when it looks like a half circle Gibbous Moon A gibbous moon is shaped like a lopsided football; a larger proportion of the moon is illuminated than is the case during a quarter moon. Waxing Moon The moon is waxing when the illuminated portion of the moon is getting a little bit bigger every day. Waning Moon The moon is waning when the illuminated portion of the moon is getting a little bit smaller every day. 1. Questions About These Definitions: To find the answers to the questions below, consult your data from the moon project, the section in the textbook entitled Phases of the Moon (p.?618–619), and Figure 21.27 on p. 618. a. How does a 1st quarter moon look different from a 3rd quarter moon? (Hint: think about whether they are lit on the right or left side) b. How does a waxing crescent moon look different from a waning crescent moon? c. How does a waxing gibbous moon look different from a waning gibbous moon? 2. The cause of the moons phases: a. Where does the moon get its light from? b. What proportion of the moon is illuminated at any time? c. What phase is the moon in when it lies between the Sun and Earth? Why? d. What phase is the moon in when the earth lies between it and the sun? Why? C. L