Power Point notes that I use in class. I did not make this presentation. I got it from the internet, the reference is on the first page. I may have altered it from it\'s origninal state though.
21. Moon Phases New Moon – the moon is between the sun and the earth, and we see the unlighted side. No lighter area of the moon is visible from Earth. As the sun continues to move, part of the moon becomes visible. When the size of the visible portion is increasing , and we first see a sliver of the moon, it is called the waxing-crescent phase
22. When the moon has moved through one quarter of its revolution, the moon looks like a semicircle, called a first-quarter phase . The lighted portion of the moon continues to increase , making it larger than a semicircle which is called the waxing-gibbous phase.
23. Halfway through its orbit, the Earth is in between the Sun and the Moon, creating a full moon phase. The entire half of the moon is reflecting light off the sun at this phase The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase. The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase. The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase. The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase. Eventually, the moon reaches a semi-circle again, called the last-quarter phase. The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase. Eventually, the moon reaches a semi-circle again, called the last-quarter phase. The moon continues, now decreasing in the amount of lighten surface. When the moon is not full anymore, but decreasing back to a semicircle, it is called a waning-gibbous phase.
24. Eventually, the moon reaches a semi-circle again, called the last-quarter phase . The light continues to decrease , when finally only a sliver of the moon is visible, which is called the waning-crescent phase.
25. The moon is now back where it started, and the process repeats. The whole process takes 29.5 days (an extra 2 days is needed from the 27.3 days for the moon to get back to its original position) This means that you usually have one of each phase per month. Sometimes, two full moons happen in one month. The second full moon of a month is usually called a blue moon .
30. The Calendar For a long time, people measured the passage of time by keeping track of the phases of the moon. Eventually, calendars were developed to keep more accurate track of time. The three basic units of a calendar – day, month, and year – are determined by the movements of the Earth and moon. A day was defined as the time it takes the Earth to rotate once. A month was defined as the time required for the moon to go through once cycle. A year was defined as the time it took the Earth to go around the Sun.
31. Sounds simple, however it was soon discovered that these were not whole numbers. The Earth takes 365.24 days to go around the sun. A year with 365 days was too short, 366 too long. The moon makes a complete cycle of phases in 29.5 days. 29 days are therefore too short for a month, 30 too long. Modern calendars were invented to fix these problems.
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