Understanding the Phases of the Moon: A Table Approach, Study notes of Physics

Download Understanding the Phases of the Moon: A Table Approach and more Study notes Physics in PDF only on Docsity! BROCK UNIVERSITY ASTR 1P01 Introduction to Astronomy I Phases of the Moon Dr. S. D’Agostino The lecture notes present a very nice series of diagrams using which you can determine, for a given phase of the Moon, when the Moon rises and sets, and during which part of the day the Moon is visible. You can also determine what the phase of the Moon is given when it rises or sets relative to the Sun. In talking to students about this in my office over the past little while, it occurred to me that some students were having difficulties understanding the series of diagrams, and so I wondered whether another method might be helpful. Here’s what I came up with. The key facts that you must remember (or, better, understand) are that the Moon rises at sunset and sets at sunrise when it is full, and that the Moon rises at sunrise and sets at sunset when it is new. Does this make sense? When the Moon is full or new it is aligned with the Earth and Sun, with the Moon between the Sun and Earth when it is new and on the opposite side of the Earth when it is full. Think about this and draw diagrams to make sure you understand it. (You can also refer to the several diagrams in Dr. Mitrović’s lecture notes and the textbook.) Let’s record these key facts in a table: Moon’s Phase Moon Rises Moon Sets new sunrise sunset full sunset sunrise new sunrise sunset The next important fact that you should remember (or, better, understand) is that each day the Moon rises and sets about 50 minutes later than on the previous day. This fact alone allows us to draw many conclusions based on the table above. For example, when the Moon’s phase is a waxing crescent, it rises after sunrise and sets after sunset, because the waxing crescent phase occurs in the days following a new phase and before the first quarter phase. Some people may prefer to fill in the table a little more, as follows: Moon’s Phase Moon Rises Moon Sets new sunrise sunset Q1 mid-day middle of night full sunset sunrise Q3 middle of night mid-day new sunrise sunset Other students may prefer to fill in the table completely, as follows: Moon’s Phase Moon Rises Moon Sets new sunrise sunset waxing crescent between sunrise and mid-day between sunset and middle of night Q1 mid-day middle of night waxing gibbous between mid-day and sunset between middle of night and sunrise full sunset sunrise waning gibbous between sunset and middle of night between sunrise and mid-day Q3 middle of night mid-day waning crescent between middle of night and sunrise between mid-day and sunset new sunrise sunset Can you understand the changes in the Moon’s rising times during a cycle of its phases? Run down the second column of the table to see if you understand: When the Moon is new, it rises at sunrise. Each subsequent day of the cycle the Moon rises a little later. By the first quarter, the Moon is rising about half-way between sunrise and sunset, sometime in the middle of the day. The Moon continues to rise later and later each subsequent day, until by the time it is full it rises at sunset. After that, the Moon continues to rise a little later each day, as the table indicates. By the time the Moon is new again, the cycle has completed, and then it repeats. Now run down the third column of the table to understand the changes in the Moon’s setting times during its cycle of phases. The discussion of the last few paragraphs should allow you to understand how to answer Q39–Q42 on Test 1. For example: • Q39: Run down the second column of the table until you reach the cell just before sunset; the corresponding phase, which you can see by looking to the left at the cell in the first column, is waxing gibbous. • Q40: Run down the second column of the table until you reach the cell just before sunrise; the corresponding phase, which you can see by looking to the left at the cell in the first column, is waning crescent. • Q41: Run down the third column of the table until you reach the cell just before sunset; the corresponding phase, which you can see by looking to the left at the cell in the first column, is waning crescent.