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Motions of the Moon

Longitudinal Study:  "The Motions of the Moon"

(GNU Free Documentation License; Wikipedia, "Phases of the Moon")


 Mark Pichaj (and the students of PHSC 102, Physical Science Lab, at Biola University).


How does the position and appearance of the Moon change in the night sky from night to night, and month to month?

A Full Moon

(From wikimedia commons)


   Grade Four / Earth Sciences

  1. Objects in the sky move in regular and predictable patterns. As a basis for understanding this concept:
    1. Students know the patterns of stars stay the same, although they appear to move across the sky nightly, and different stars can be seen in different seasons.
    2. Students know the way in which the Moon's appearance changes during the four-week lunar cycle.
    3. Students know telescopes magnify the appearance of some distant objects in the sky, including the Moon and the planets. The number of stars that can be seen through telescopes is dramatically greater than the number that can be seen by the unaided eye.
    4. Students know that Earth is one of several planets that orbit the Sun and that the Moon orbits Earth.
    5. Students know the position of the Sun in the sky changes during the course of the day and from season to season.
  Grade Five / Earth Sciences
  1. The solar system consists of planets and other bodies that orbit the Sun in predictable paths. As a basis for understanding this concept:
    1. Students know the Sun, an average star, is the central and largest body in the solar system and is composed primarily of hydrogen and helium.
    2. Students know the solar system includes the planet Earth, the Moon, the Sun, eight other planets and their satellites, and smaller objects, such as asteroids and comets.
    3. Students know the path of a planet around the Sun is due to the gravitational attraction between the Sun and the planet.

  Grade Eight / Earth in the Solar System (Earth Sciences)

  1. The structure and composition of the universe can be learned from studying stars and galaxies and their evolution. As a basis for understanding this concept:  
    1. Students know galaxies are clusters of billions of stars and may have different shapes.
    2. Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature, and color.
    3. Students know how to use astronomical units and light years as measures of distances between the Sun, stars, and Earth.
    4. Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own light.
    5. Students know the appearance, general composition, relative position and size, and motion of objects in the solar system, including planets, planetary satellites, comets, and asteroids. 

 [What's funny about this—but not a laughing matter—is that although these are elementary and middle school standards, I doubt most college students remember or understand the progression of phases of the Moon.  In fact, I wonder how many adults do!]

Experimental Design

Given the nature of observational astronomy, this study is primarily observational rather then experimental.  (A late Victorian scientist like Henry Moseley would have despised it; he specifically excluded "astronomy and other purely observational" sciences from a monetary prize he founded.)  Using the same time and position for observation, the phases of the Moon, and its position in the night sky for at least one week, will be plotted on the same diagram for comparison purposes.  

Further study would include libration, the two sides of the Moon, Lunar surface features, selenology (lunar geology), the shape of the Moon's orbit, declination from the ecliptic plane, eclipses, and the Moon's eventual fate (given sufficient time). 

Independent variable

The time of the night when the Moon will be observed.

Dependent variables

The change in position (azimuth and elevation angles) from a reference horizon and the change in phases (periodic lighting, shadowing, and appearance) of the Moon.

Series & Controls

Given current budgetary and technological limitations, this study will be performed on only one natural satellite in the Solar System, Terra's Luna.  (However, given the permutations of the Moon's orbit, this still allows for a great deal of data to be collected over time.)


(1)  A compass, with which to determine South and to measure azimuth.

(2)  An elevation-measuring device.  (A simple one can be made from a large protractor, a drinking straw taped to the straight edge of the protractor as an aiming device, and a weighted string hanging from the protractor's index hole to serve as a plumb bob from which to measure 90° elevation.)

(3)  A clipboard with paper and pencil to construct the diagram.  (Graph paper can be useful.)

(4)  Depending on the time of year and the weather, warm clothes.

(5)  A near-fresh New Moon.


(1)  Observation of the Moon should be planned to begin a few days after the New Moon.

(2)  It should be planned so that the observer is able to occupy the same position and is free to observe the phases of the Moon during the same time every evening for at least one week.

(3)  Using the compass, the observer should face due South, and draw an outline of the horizon as she sees it from her Observation Position (OP). 

(4)  Beginning with the first night, use the compass to determine the azimuth angle of the Moon from due South and the protractor to determine the angle of elevation above the horizon, and record this data on your diagram.

(5)  In the proper position on the diagram, sketch as accurately as possible the shape of the Moon.

(6)  Repeat this process for at least one week.  (Ten to fourteen days would give a better picture of how lunar phase change progresses.) 

(7)  NB:  Be sure to occupy the same OP at the same time every evening for most accurate results.

Sample data and graphs

(1)  The best evidence for this section would be scanned and digitized copies of student work.  Unfortunately, none are available at this time.
(2)  In place of the above, here is the best animation of how the phases appear from Earth, given the position of the Moon in space.
(3)  And here is an even better view of the progression of the phases!

(From wikimedia commons)

Photographs and Movies

(1)  An excellent "Lunar Phase Simulator" from the University of Nebraska-Lincoln.

(2)  Two good animations about "Phases of the Moon" and "Why We See Phases" from Valdosta.

(3)  An elementary school level tutorial & animation from Wonderville in Canada.  

(4)  An animation of the phases from Sumanas.

(5)  An animation of how the Moon's phase appear from Earth.

(6)  An animated video tutorial about Moon Phases ,with some nice, soothing background music.  (Please note that the phases are shown as viewed from the Southern Hemisphere.)

Moon Phases

(7)  A video from the History Channel about phases of the Moon.

The Universe: The Phases of the Moon


(1)  Lunar phases diagrammed and explained:

(2)  A "lunar calendar" from StarDate Online:           

(3)  USNO "Complete Sun and Moon Data for One Day":

(4)  USNO "Phases of the Moon":        

(5)  USNO "Moon Phase Images":                       

(6)  A "Moon & Earth Phase Viewer":

(7)  "Celestial Coordinate System" for finding the position of celestial bodies:

(8)  A list of recommended software for modeling lunar phases: