The Moon Project: Descriptions of Topics

Transcription

1 The Moon Project: Descriptions of Topics 2003 Ann Bykerk-Kauffman, Dept. of Geological and Environmental Sciences, California State University, Chico * Questions to Answer: Topic #1: Moon Rise and Set 1. We all know that the sun rises in the east and sets in the west. But what does the moon do? Does it rise in the east and set in the west (like the sun does)? Or, since we know that the moon revolves around Earth from west to east, does the moon rise in the west and set in the east (the opposite of what the sun does)? Prove your answers using your observations. Explain WHY the moon rises where it does and sets where it does. 2. The sun always rises in the morning and sets in the evening. The moon, on the other hand, rises and sets at any and all times of the day or night. Why? Is there any pattern to the changes in the times of moon rise and set? What is that pattern? Why does that pattern exist? 3. Is there any correlation between the times of moonrise/moonset and the phases of the moon? If so, clearly explain that correlation and explain and illustrate WHY this correlation exists. Observations to Make 1. Make the general observations, as described on page MP-2, that each person must make, regardless of topic. 2. For EVERY observation, note the compass direction of the moon (is it in the NE, E, SE, S, SW, W or NW part of the sky?). To assure accuracy, use a compass and/or refer to a map. WARNING: In Chico, the streets are crooked; they are NOT lined up with N, S, E and W. 3. On at least 10 days (or nights), observe the moon twice on the same moon day, at least four hours apart. In other words, after a given moon rise, observe the moon twice before it sets again. Each time, draw the moon exactly as you see it, record the position of the moon in the sky (relative to N, S, E, W and up ) and make a sketch of the trees and houses in the foreground. Put all of this information in the table entitled Extra Data Tables for Topics #1 and #2. Use the given moonrise and moonset times on the Table of YOUR Moon Observations to determine good dates and times for making your double observations at least four hours apart. For example, on Sunday, February 9, you will be able to see the moon all afternoon and evening. You could observe it at 2:00 p.m. and then again at 9:00 p.m. The longer the time lapse between your observations, the better, but it is sometimes hard to find the moon in the middle of the day. So watch for opportunities to make two observations in the dark. For example, on Friday, February 14 th, you could observe the moon at 7:00 p.m., just before going out for a romantic evening, and then a second time when you make your way home during the wee hours of Saturday morning, February 15 th (as long as it's before moonset at 6:31 a.m.). Or you could observe the moon on Tuesday, February 18 th at 9:00 p.m., about an hour after it rises. Then, you could observe the same moon again the next morning (Wednesday, February 29 th ) at 7:30 a.m., about an hour before it sets. Note that both observations may or may not be on the same calendar date. That doesn't matter as long as both observations are made on the same moon day. * Supported by NSF Grant # Permission is granted to reproduce this material for classroom use. MP 3

2 MP 4 The Moon Project: Descriptions of Topics What to Graph: The table entitled Moon Facts for the Year 2003 lists times of moonrise and moonset for each date in the year Use the data on this table to complete the graph for Topic #1, depicting the time when the moon is out for each date between January 1 and April 30, If you are confused as to how to complete this graph, see the example graph for Topic #1. A word to the wise: Complete your graph as early as possible and have your lab instructor check it. You already have all of the data you need to complete the graph. The completed graph will help you understand your topic better. Hints For Figuring Out the Answers to Your Questions: Fill in the blanks below. Can you draw similar diagrams for other positions of the moon? Why to east and west seem to be in opposite directions on the two diagrams? How do these diagrams relate to your topic questions? E W E W Moon rise / set Approximate Time of Day Phase of the moon Moon rise / set Approximate Time of Day Phase of the moon

3 The Moon Project: Descriptions of Topics MP 5 Topic #2: The Angle of the Illuminated Portion of the Moon to the Questions to Answer: 1. The angle of the lit portion of the moon relative to the horizon changes. For example, sometimes the crescent moon looks like a crooked smile ( ); other times it looks like a hat cocked at an angle ( ). The lit portion of the moon doesn't really rotate, so why does it look like it does? What is REALLY happening? 2. As the moon makes its arc across the sky, how many degrees does the lit portion seem to rotate 1 per hour? 3. The pattern made by the lunar maria (see Fig on p. 579 of your textbook) is always the same but it is not always at the same orientation sometimes the rabbit in the moon is right side up; sometimes it is upside down. Why does this pattern of lunar maria appear to change orientation? Observations to Make a. Make the general observations, as described on page MP-2, that each person must make, regardless of topic. b. On at least 10 days (or nights), observe the moon twice on the same moon day, at least four hours apart. In other words, after a given moon rise, observe the moon twice before it sets again. Each time, very carefully record the following on the Extra Data Tables for Topics #1 and #2: (1) Record the position of the moon in the sky (relative to N, S, E, W and up ) and make a sketch of the trees and houses in the foreground. (2) Draw the moon so that the angle of the lit portion of the moon relative to the horizon is accurately shown. This can be difficult to do correctly if the moon is high in the sky. So be sure to always face the moon as directly as possible, then draw the moon as seen relative to the point on the horizon directly in front of you (i.e. the spot where you can draw an imaginary line straight up to the moon without going past the zenith or going sideways see diagram below). angle of lit portion of moon to horizon line straight up to the moon line (3) Observe and illustrate the locations of the darker portions of the moon's surface, called the lunar maria (pronounced like the name Maria, except with the accent on the first syllable instead of the second). 1 I do mean rotate, not revolve. In other words, I mean the change from a hat to a smile, not the movement of the moon across the sky (the Topic 1 folks will worry about that).

4 MP 6 The Moon Project: Descriptions of Topics Use the given moonrise and moonset times on the Table of YOUR Moon Observations to determine good dates and times for making your double observations at least four hours apart. For example, on Sunday, February 9, you will be able to see the moon all afternoon and evening. You could observe it at 2:00 p.m. and then again at 9:00 p.m. The longer the time lapse between your observations, the better, but it is sometimes hard to find the moon in the middle of the day. So watch for opportunities to make two observations in the dark. This works best when the moon is up most of the night. For example, on Friday, February 14 th, you could observe the moon at 7:00 p.m., just before going out for a romantic evening, and then a second time when you make your way home during the wee hours of Saturday morning, February 15 th (as long as it's before moonset at 6:31 a.m.). Or, if you are an early to bed, early to rise type of person, you could observe the moon on Tuesday, February 18 th at 9:00 p.m., about an hour after it rises. Then, after you get a good night s sleep under the bright moonlight, you could observe the same moon again the next morning (Wednesday, February 29 th ) at 7:30 a.m., about an hour before it sets. Note that both observations may or may not be on the same calendar date. That doesn't matter as long as both observations are made on the same moon day. c. On at least one day (or night), when the moon is shaped like a crescent or half circle, observe the moon at least 6 times on the same moon day. All observations should be at least one hour apart. Each time you make your observation, very carefully record the data described under b above. What to Graph: 1. Complete the graph of the Angle of the illuminated portion of the moon to the horizon vs. the Time of day the Observation Was Made. The angle values have already been written on the left side of the graph for you. But YOU must write in the appropriate observation times on the graph yourself; be sure to include a.m. or p.m. as appropriate. The bold lines on the graph should be one hour apart. For example, if you made your first observation of the moon at 8:41 a.m. and the angle between the horizon and the illuminated portion of the moon was 22, the graph would look like this; you would then add five more data points for the remaining five observations. Graph For the Six Observations in One Moon Day Angle of the Illuminated Portion of the Moon to the a.m. 9 a.m. 10 a.m. 11 a.m. 12 noon 1 p.m. 2 p.m. 3 p.m. Time of Day the Observation Was Made

5 The Moon Project: Descriptions of Topics MP 7 2. Complete the graph of the Apparent Rotation of the Illuminated Portion of the Moon vs. the Time Lapse Between Observations. Do this as follows: a. For each of the 10 times that you observe the moon twice in one moon day, measure the angle between the longest dimension of the illuminated portion of the moon and the horizon for both the before and after observations. The examples below illustrate the method to use for both crescent and gibbous moons. Crescent Moon Before (first observation) After (several hours later) Gibbous Moon Before (first observation) After (several hours later) b. The moon doesn't really rotate, but it appears to. Measure the apparent angle of rotation of the illuminated portion of the moon that seems to have occurred between your two observations. The examples below illustrate the method to use for both crescent and gibbous moons = = 94 Crescent Moon Gibbous Moon Crescent Moon: As shown above, the angle between the moon and the horizon was 127 at the time of the first observation; at the time of the second observation, the angle was only 48. So the moon appears to have rotated 79 clockwise.

6 MP 8 The Moon Project: Descriptions of Topics Gibbous Moon: As shown on the previous page, the angle between the moon and the horizon was 116 at the time of the first observation; at the time of the second observation, the angle was only 22. So the moon appears to have rotated 94 clockwise. c. Calculate the number of hours elapsed between your first and second observations. For example, if you took one measurement at 5:00 p.m. and one measurement at 12:00 midnight, the Time Lapse Between Observations was 7 hours. d. For each pair of measurements, plot one data point on the graph for Topic #2 ( Amount of Apparent Rotation of the Illuminated Portion of the Moon vs. Time Lapse Between Observations ). The horizontal (X) axis point should be the amount of elapsed time between the two observations you made; the vertical (Y) axis point should be the apparent angle of rotation of the moon during that time. e. When you have plotted all of your data points, see if there is any consistent relationship between the amount of apparent rotation of the illuminated portion of the moon and the time lapse between observations. Note: if the data points make a line, even if it is rough, then there IS a consistent relationship that can be approximated by drawing in a best fit line. Hints For Figuring Out the Answers to Your Questions: In the diagram below, the moon is on the left and Earth is on the right. You are looking down on the North Pole. The diagram shows one person standing at the equator and moving with Earth as it rotates on its axis. The person is shown in four different positions, six hours apart. One time is at moon rise, one is at moon set, one is at the point when the moon is directly overhead, and one is when the moon is not out at all. Which is which? What does the moon look like to that person at each time? What phase is it in? Does the moon appear to be lit on the top, bottom or side? Over the 12 hours that the moon is out, which way does the moon appear to rotate? How would all of this look different to a person at 40 N. latitude (i.e. the latitude of Chico)?

7 The Moon Project: Descriptions of Topics MP 9 Questions to Answer: Topic #3: Length of the Moon Day 1. We all know that the sun is up much longer each day in the summer than it is in the winter. The length of time that the moon is up each moon day also varies. Describe how and why the length of the moon day varies over the course of one moon cycle. 2. Every day, the moon follows an arc-shaped path across the sky. It first appears at the horizon, then gradually rises up as it travels across the sky. At the half-way point, the moon reaches a maximum altitude (height above the horizon) for that day. Beyond the half-way point, the moon sinks lower and lower as it continues to travel across the sky until, finally, the moon drops out of sight below the horizon. The maximum altitude reached by the moon is not the same every day. Some days it s so high, you have to crane your neck to see the moon; other days, it s only about a third of the way up from the horizon. Describe how and why the daily maximum altitude (height of the moon above the horizon) varies over the course of one moon cycle. 3. The moon is out longest during different phases at different times of the year. For example, sometimes the moon is out longest during the full moon phase but sometimes the moon is out longest during the waxing crescent phase, etc. There is a definite pattern to the month of the year and which phase of the moon is out longest; clearly and fully describe this pattern and explain why this pattern exists. 4. The maximum daily altitude of the moon varies in a systematic way with regard to moon phase and season. For example, in December, the full moon gets very high in the sky but in June the full moon never gets very high above the horizon. Explain how and why this is true, giving specific examples for each season. Hint for the why? parts of all of the above questions: The 5 tilt of the moon's orbit around Earth has a slight influence on the length of the moon day and height of the moon in the sky, but it is not the main influence. Thus I suggest you ignore this effect completely. There's another bigger influence; focus on that. Observations to Make a. Make the general observations, as described Page MP-2, that each person must make, regardless of topic. b. At least five times (preferably more), time your observation so that you observe the moon near its highest point, half-way along its journey across the sky and half-way in time between moonrise and moonset. For each of these special observations, sketch the moon as usual and measure the altitude of the moon (the angle between the moon and the horizon between 0 and 90 ), following the procedure described on the next page. Record these special observations and altitude measurements in the Extra Data Table for Topic #3 Altitude of the Moon At its Highest Point.

8 MP 10 The Moon Project: Descriptions of Topics Make these special observations about a week apart and near the dates of the new, 1st quarter, 3rd quarter and full moon phases. Use the given moonrise and moonset times to determine good dates and times for observing the moon at its highest altitude for any given day. For example, on Sunday, February 9 th, the moon will be in its First Quarter phase. It will rise at 11:23 a.m. and set at 1:53 a.m. the next morning (February 10 th ). Thus, it will be at its highest point at 6:37 p.m. on Sunday, February 9 th. Here's a second example: on Sunday, February 23 rd, the moon will be in its Third Quarter phase. It will rise at 12:56 a.m. and set at 11:01 a.m. Thus it will be at its highest point at 5:59 a.m. How to Measure the Altitude of the Moon: We will make and use a very simple instrument called a theodolite; materials will be provided in lab. To construct the theodolite, tape a drinking straw to the straight edge of a protractor as shown in the adjacent diagram. 2 Place the eraser end of a pencil against the hole in the protractor and insert a pushpin through the other side of the hole into the eraser the pencil serves as a convenient handle. Next, tie a plumb bob (a string attached to a weight) to the needle part of the push pin. To use the theodolite to measure the altitude of the moon, look through the straw at the moon, holding the straw as steady as possible. Let the plumb bob hang freely. Have a partner read the angle (we ll call it α) through which the string passes. Or, if you are alone, let the plumb bob hang freely as you look at the moon. Then, hold the string in place against the protractor as you lower it and read the angle. The altitude of the moon will be 90 - α. Eyepiece Pencil Straw α Plumb bob To the Moon What to Graph: The table entitled Moon Facts for the Year 2003 lists the length of the moon day (# of hours the moon is up) for each day this year. Use the data on this table to complete the (sixpage!) graph of the # of Hours the Moon is Out. A word to the wise: Complete your graph as early as possible and have your lab instructor check it. You already have all of the data you need to complete the graph. The completed graph will help you understand your topic better. 2 This diagram is modified from Figure 3 of the Reckoning Latitude experiment on p. 200 of Conceptual Physical Science Laboratory Manual (2 nd edition), by Paul Hewitt, John Suchocki and Leslie Hewitt: Addison-Wesley, 1999.

9 The Moon Project: Descriptions of Topics MP 11 Hints For Figuring Out the Answers to Your Questions: The diagram below shows moon rays coming toward Earth from a moon that is toward the right, beyond the edge of the paper. This diagram also shows the horizon for a person standing at 40 N Latitude on the side of Earth that can see the moon. Note the angle between the moon rays and the horizon. The curved line is the path that this person takes (even while standing still!) as Earth rotates about its axis. Note the line that splits this path. This line divides the part of Earth that can see the moon from the part of Earth that cannot see the moon. Can the person at 40 latitude see the moon for more than 12 hours/day or less than 12 hours/day. How do you know? Now, think about where the sun is. What if the sun were also toward the right but WAY beyond the edge of the paper. What phase is the moon in? How do you know? What season is it? How do you know? What if the moon were on the left side of Earth and the sun were still on the right side? How would your answers to the above questions be different? How would you redraw the diagram to fit this situation? What if the sun were on the left? How would your answers to the above questions be different? What if the sun were high above the paper, shining down on Earth? How would your answers to the above questions be different? What if the sun were underneath the paper, shining up toward Earth? Again, how would your answers to the questions be different? Moon Rays Cannot see the moon Can See the Moon

10 MP 12 The Moon Project: Descriptions of Topics

11 The Moon Project: Descriptions of Topics MP 13 Questions to Answer: Topic #4: Synodic and Sidereal Months 1. The amount of time that the moon is out on any given day (or night) varies considerably. In Chico, the amount of time the moon is out ranges from 9 1/2 hours to 15 1/2 hours (See the table on entitled Moon Facts for the Year 2003 ). We know that the sun is out the longest on the summer solstice (± June 21). After that date, the days gradually get shorter and shorter until the winter solstice (± December 21), the shortest day of the year. After the winter solstice, the days gradually get longer and longer until the next summer solstice. In scientific terms, the number of hours that the sun is out increases and decreases in a cycle with a periodicity of one year. The number of hours that the moon is out also increases and decreases in a cycle. What is the periodicity of that cycle? Is it one synodic month? One sidereal month? One year? Or something else altogether? Use one of your graphs to prove your answer. Why does that cycle have the length that it does? Draw diagrams to illustrate your answers. 2. What do the longest moon days of all moon cycles have in common (this should fall out of one of your graphs)? Why? What do the shortest moon days of all moon cycles have in common? Why? What do the average-length moon days of all moon cycles have in common? Why? Draw diagrams to illustrate your answers. 3. The moon, like the sun, travels through the constellations of the Zodiac. How long does it take the moon to go through all of the constellations of the Zodiac? Does it take a synodic month? A sidereal month? A year? Or something else altogether? Why? 4. How do we know that it takes the moon exactly 27 1/3 days to complete a 360 orbit of Earth (a sidereal month)? Hint: one of your graphs should provide the information you need. Observations to Make: a. Make the general observations, as described on page MP-2, that each person must make, regardless of topic. b. Whenever you observe the moon at night (at least 10 times), try to figure out what constellation the moon is in (use your Star and Planet Locator). In the far right column of the Table of YOUR Moon Observations, show the moon and any stars (or planets) that you see around the moon. What to Graph: a. You will plot the astronomical place of the moon for each date between January 1 and April 30, Get this information from the table entitled Moon Facts for the Year Plot this information on the graph entitled Astronomical Place of the Moon. b. The table entitled Moon Facts for the Year 2003 also lists the length of the moon day (# of hours the moon is up) for each day this year. Use the data on this table to complete the (six-page!) graph of the # of Hours the Moon is Out.

12 MP 14 The Moon Project: Descriptions of Topics c. On your graph of the # of Hours the Moon is Out, label the astronomical place of the moon next to each data point representing each of the following: i. an average-length moon day ( 12 1/2 hours). ii. the longest moon day of a cycle (this will show up as an obvious hump on the graph) iii. the shortest moon day of a cycle (this will show up as an obvious low spot on the graph) A word to the wise: Complete your graphs as early as possible and have your lab instructor check it. You already have all of the data you need to complete the graph. The completed graph will help you understand your topic better. Hints For Figuring Out the Answers to Your Questions: The diagram below shows moon rays coming toward Earth from a moon that is toward the right, beyond the edge of the paper. This diagram also shows the horizon for a person standing at 40 N Latitude on the side of Earth that can see the moon. Note the angle between the moon rays and the horizon. The curved line is the path that this person takes (even while standing still!) as Earth rotates about its axis. Note the line that splits this path. This line divides the part of Earth that can see the moon from the part of Earth that cannot see the moon. Can the person at 40 latitude see the moon for more than 12 hours/day or less than 12 hours/day. How do you know? Now, think about where the various Zodiac constellations are. In the diagram below, what is the astronomical place of the moon, relative to these constellations? How do you know? What if the moon were on the left side of Earth? How would your answers to the above questions be different? How would you redraw the diagram to fit this situation? What if the moon were high above the paper, shining down on Earth? How would your answers to the above questions be different? What if the moon were underneath the paper, shining up toward Earth? Again, how would your answers to the questions be different? Moon Rays Cannot see the moon Can See the Moon