The Earth's Moon
by Debbie Simpler
e-mail: Simpler@esuvm.emporia.edu
05-04-99

This page was created in order to satisfy requirements for an assignment in Earth Science Lab at Emporia State University. This project is in conjunction with Chapter 12,   "The Moon," found in the Introduction to Earth Science Lab book, written by: Paul Johnston, Susan Aber, and Hengchun Ye (1998).  Edina, MN: Burgess Publishing.

This image was taken from: Lorenzo Pasqualis's site on, A View of the Moon

The moon orbits around the Earth while the moon and Earth system orbits around the sun.  The time it takes the Earth to orbit the sun we call one year.  Like this cycle, the time it takes the moon to orbit the Earth is called a month.  In one month's time, an observer from Earth will see many phases of the moon.  Phases, as seen by an observer, consist of the moon changing shape in the sky or different amounts of the lighted side are visible.  An observer would also see the moon at different times during the day throughout the monthly cycle.
 

 
 
 
 

Moon Phases

The Earth and moon are partially lighted at all times, but the moon is not always seen at full phase because of the location of the moon with respect to the Sun and Earth.  Observers standing on Earth see different phases of the moon or differing percents of of the lighted side of the moon.  There are eight different phases thatan observer on Earth would see during one month.  They are, listed in order of appearance, New Moon, New Crescent, First Quarter, New Gibbous, Full Moon, Old Gibbous, Last Quarter, and Old Crescent.
 

This image was taken from an online astronomy course at Cornell University. To see more diagrams on moon phases click here
 
 
   The New Moon is observed when the moonis directly in line with the Sun and Earth.  The moon is interferingwith the lighted side of the Earth and therefore cannot be seen by an observeron Earth because the moon's dark side is facing Earth.  Occasionallythe moon's orbit will intersect the Earth's plane of revolution, which is called a node position and is in a perfect line between theEarth and the Sun.  When this occurs, a viewer on Earth will observethe Sun slowly disappear because the moon obscures the Sun from view. This unusual occurrence is called a solar eclipse.


   The New Crescent phase is the second phase.  The New CrescentMoon appears approximately 2.66 days after the new moon (Alter, pg. 4). During this phase, the moon is still very close in line with the sun, therefore,by the time the sky is dark enough to see the moon it is very low in the west. 


When the First Quarter moon is visible this means the moon is directly in line so that the Earth and moon both are getting the same amount of sunlight.  An observer from Earth sees a half moon, therefore, the moon's side that is facing the Sun is observedon Earth and the other half of the moon is facing away from the Sun and is unable to be seen from Earth.


   The New Gibbous, or sometimes referred to as the Waxing Gibbous, is the fourth phase of the moon observed from Earth, or the last phase before the moon becomes full.  The New Gibbous phase usually last between two and three days before the full moon is exalted  (Alter, pg. 4).


   The Full Moon is observed when the Sun, Earth, and Moon are in a straight line and the moon's lighted side is behind the Earth in alignment with the sun.  During the full moon phase, the moon rises high off the horizon.  At this time, the details of the moon are most visible.  Once in a while the moon will orbit on a node.  At this time the moon is perfectly in line with the Earth and graduallybecomes shadowed so it is not visible on Earth.  Soon the moon will gradually orbit out of the shadow of the Earth and once again become visible.  This phenomenon is referred to as a lunar eclipse.
 

The three phases after the full moon are the exact replica of the previous phases before the full moon, except that the sides that are lit are on the opposite side of the moon.  The shadow of the Earth continues to cross the moon in the same direction, causing the opposite side to be shadowed.  The sixth phase is called the Old Gibbous, also referred to as the Waning Moon.  The Old Gibbous phase is formed directly after the full moon.  As theMoon continues to orbit in the Earth's shadow the moon will enter the Second Quarter phase and proceed to the Old Crescent, and finally backto the New Moon.  The cycle begins all over again, beginning a new month.

   

Old Gibbous       Last Quarter       Old Crescent      


 

Week Lengths
 

During the Babylonian time period the moon was considered a God.  Gods were considered the power of life and experiences, therefore, should be worshiped.  The creation of the week length is much less scientific as the length of a month.  Every full moon represented a new month and this was reason for a celebration.  The celebration consisted of worship, eating, drinking and dancing, and everyone was off work that day.  The celebration of the first of the month which was called Sappatu and soon translated into English as the Sabbath.

Every time the full moon would appear a celebration would begin and the economy would flourish and the productivity expanded.  The Babylonian people thought the Gods were working miracles. In order to satisfy the Gods, the Babylonian's took the new moon off as well in order to worship.  The work production continued to rise so the Babylonians celebrated the quarter moons as well.  Now the Babylonians had four days off a month and they usually fell seven days apart.  Once in a while the phases would be on the eighth day.  In order to ease the confusion the Babylonian's stopped having the "Sabbath" accordingto the moon phases.  Instead, the Babylonian people decided to worship every seventh day.  The number seven became magic to the Babylonian people, hence, the seven days of the week.  Therefore, the days of the week were named after the seven planets (that they knew), which were considered Gods by the Babylonian's.

When the Roman empire converted to Christianity, the seven days a week became official,and the seventh day was a day of worship and rest.

After World War II, the second day in the week was observed because there were too many workers.  The seventh day was our Saturday, which was considered the Sabbath. In consideration for the Jews, the first day of the week was also considered a holy day of rest as the Jews interpreted the Bible.

To learn more about the moon, seasons, and calendars, visit: Larry Freeman's page on time development.
 
 
 
 References

"The Phases of the Moon", http://astrosun.tn.cornell.edu/courses/astro201/Moon_phase_pict.htm

Alter, Dinsmore (1993). Pictorial Guide to the Moon.  NY: Thomas Y. Company.

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