• Moon Phases


    I can demonstrate the relative positions of the sun, Earth, and moon during the moon phases and to observe the changing appearance of the moon as seen on Earth.

    Learning Standard:

    ES 9.  Describe lunar and solar eclipses, the observed moon phases, and tides. Relate them to the relative positions of the earth, moon, and sun.

    Earth’s Moon Notes:

    Motions of the Moon

    a. Moon’s revolution around Earth
    i. Moon completes one revolution in 27.3 days
    ii. Revolution causes moon phases

    b. Moon’s rotation on its axis
    i. Moon completes one rotation in 27.3 days

    c. You always see the same side of the moon because the moon’s periods of rotation and revolution are almost equal.  This means that the time it takes the moon to orbit the Earth is almost the same as the time it takes to rotate once, causing humans to always see the same side of the moon from Earth.

    See Figure A

    (Figure A)  Image source:  http://astrobob.areavoices.com/2011/05/17/mysteries-of-the-moons-far-side/


    Moon phases

    a. Moon phase: the changing appearance of the moon as seen from Earth

    i. One full cycle of moon phases = 29.5 days or about 1 month.  See Figure B

    ii.  The moon phase cycle as seen from Earth takes a little bit longer than the moon’s revolution because while the moon is orbiting the Earth, the Earth is constantly moving because it is orbiting the sun.  The Moon therefore travels slightly more than 360° to get from one new moon to the next. Thus the lunar month is longer.


    moon phases diagram
    (Figure B)  Image source:  http://www.moonconnection.com/moon_phases.phtml