LAB 04 - THE MOTION OF THE MOON

THE MOTION OF THE MOON

Long before the invention of writing, or bookkeeping, people began to notice certain regularities in the motions of the celestial bodies (sun, moon, planets, and stars).  Since there was a noticeable pattern to the motions of things in the sky, it was only natural to mark the passage of time by recording the cycles of celestial objects. Measuring time by days seems to be a very natural thing to do, but it would not have been convenient for long time counting (in the days before the use of Arabic numerals and place-value numbering).  Even if the average lifespan of a primitive person was only 30 years, that would work out to almost 11,000 days which would have been most difficult for them to keep track of back then!  

The next most obvious celestial rhythm is the period of the lunar phases.  The moon waxes (get brighter) from nothing to full and back to nothing again in a definite period of time.  In fact, the word month derives from the old English word monaf meaning Moon.   Counting lunar phase cycles, the lifespan of a primitive person would average about 350 months.  The lunar month took on a special significance with the introduction of agriculture.  The success of agriculture in a primitive society meant stable homes and growing populations if crops did not fail.  The success or failure of the crops depended on being able to judge the passage of the seasons.  Early people certainly noticed that there were roughly 12 lunar months across all four seasons.  Hence, counting lunar phase cycles became as important to agriculture as it was to the earlier hunter-gatherers as a means to anticipate coming seasonal changes. 

Learning the phases of the moon was something that you probably learned in your elementary school curriculum.  In this lab, you will be asked to identify the phase of the moon on certain days in the activity.  As such, you can use the following guides to help you identify the moon phase.

In the diagram above, sunlight is coming from the right.  It shows the moon at 8 positions in its orbit around the Earth and the corresponding lunar phase that will be seen in the sky when the moon is in that position.   The following table relates the percentage illumination of the moon to each lunar phase starting at New Moon and ending at New Moon where the pattern repeats itself. 

In today's lab, you will observe the moon as it moves through the sky over a period of 30 days.  During this time, you will notice when certain phases of the moon are available for viewing.  Through this lab, you will determine the time for the completion of the cycle of lunar phases (called a synodic month) and the time it takes for the moon to complete one orbit around the Earth (called a sidereal month).  The following video contains further instructions and demonstrates how to use the Stellarium Web Online to complete this lab.  You must watch this video if you want to know how to do this lab.