Moon Phases and Topography - Laboratory #3 | ASTR 1401, Lab Reports of Astronomy

Download Moon Phases and Topography - Laboratory #3 | ASTR 1401 and more Lab Reports Astronomy in PDF only on Docsity! Astronomy 1401 Department of Physics and Geology Moon Phases and Topography Equipment Needed Quantity Moon Globe 1 Part 1: Background - Moon Phases and Topography 1.1 Moon Phases: As the Moon orbits Earth, it goes through a sequence of phases as the portion of the visible illuminated hemisphere changes, as seen from Earth. The Moon shines by reflecting the light from the Sun, and shows the characteristic phases during each orbit of Earth. The lunar orbit is elliptical. The Moon's orbital period around Earth, and also its rotation period, is 27.322 days. Since the period of the orbit is the same as the Moon's rotational period (or lunar day), we always see the same side of the Moon. The equality of rotational and orbital periods is due to tidal forces of Earth upon the Moon that causes the Moon’s orbital period and the Moon’s rotational period to be synchronous, so that the same hemisphere of the Moon always faces Earth. This face is called the Near Side, and the side not visible from Earth is the Far Side. From any location on Earth, the Moon appears to be a circular disk which, at any specific time, is illuminated to some degree by direct sunlight. Like Earth, the Moon is a sphere which is always half illuminated by the Sun. As the Moon orbits Earth we get to see more or less of the illuminated half. During each lunar orbit (a lunar month), we see the Moon's appearance change from not visibly illuminated through partially illuminated, to fully illuminated, then back through partially illuminated to not illuminated again. Although this cycle is a continuous process, there are eight distinct, traditionally recognized stages, called phases. The phases designate both the degree to which the Moon is illuminated (as seen from Earth) and the geometric appearance of the illuminated part (as seen from Earth). These phases of the Moon (see Figure 1.1), in the sequence of their occurrence (starting from New Moon), are listed below. Figure 1.1 p. 2 1. New Moon: The Moon's un-illuminated side is facing Earth. The Moon is not visible 2. Waxing Crescent: The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is visibly illuminated is increasing. 3. First Quarter: One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is visibly illuminated is increasing. 4. Waxing Gibbous: The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is visibly illuminated is increasing. 5. Full Moon: The Moon's illuminated side is facing Earth. The Moon appears to be completely illuminated by direct sunlight. 6. Waning Gibbous: The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is visibly illuminated is decreasing. 7. Third Quarter: One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is visibly illuminated is decreasing. 8. Waning Crescent: The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is visibly illuminated is decreasing. New Moon, First Quarter, Full Moon, and Third Quarter phases are considered to be primary phases, and their dates and times are published in almanacs and on calendars. The two crescent and two gibbous phases are intermediate phases, each of which lasts for about a week between the primary phases, during which time the exact fraction of the Moon's disk that is illuminated gradually changes. The phases of the Moon are caused by the relative positions of the Moon and Sun in the sky. For example, New Moon occurs when the Sun and Moon are quite close together in the sky. Full Moon occurs when the Sun and Moon are at nearly opposite positions in the sky - which is why a Full Moon rises about the time of sunset, and sets about the time of sunrise, for most places on Earth. First and Third Quarters occur when the Sun and Moon are about 90 degrees apart in the sky. In fact, the two "half Moon" phases are called First Quarter and Third Quarter because they occur when the Moon is, respectively, one- and three-quarters of the way around the sky (i.e., along its orbit) from New Moon. Following waning crescent is New Moon, beginning a repetition of the complete phase cycle of 29.5 days average duration. The time in days counted from the time of New Moon is called the Moon's "age". Each complete cycle of phases is called a "lunation". The time elapsed between phases is given in Figure 1.2 with some detail. p. 5 Rilles come in two varieties: sinuous and graben. Sinuous rilles are narrow, winding channels cut by flowing lava. Some of these channels were formed from lava tubes whose roofs have since collapsed. Graben (straight) rilles are where sections of the crust have dropped to lower levels due to faults in the crust. Normal faulting occurred as the Moon cooled, producing features like the Straight Wall (Rupes Recta), a 110 km long cliff with a 600 m drop. Latitude and longitude coordinates have been established for the Moon. The lunar latitude of any location on the Moon is the angular distance north or south of the lunar equator. Lunar longitude is the angle measure east or west of the lunar prime meridian. As with the Prime Meridian of Earth, the location of the Moon’s prime meridian is arbitrary. By international agreement, the lunar prime meridian splits the Near Side into equal eastern and western halves. This makes the lunar prime meridian pass through Central Bay (Sinus Medii). SAFETY REMINDER • Follow the directions for using the equipment. Part 2: Lab Activity - Moon Phases and Topography The purpose of this laboratory activity is to understand the different phases that the Moon goes through and identify various lunar surface features such as mountains and valleys, maria, craters and so on. 2.1 Moon Phases A. Exercise 1: Figure 2.1 shows Earth, the Sun and five different possible positions for the Moon during one full orbit (dotted line). For each of the five positions of the Moon shown below, the Moon has been shaded on one side to indicate the half of the Moon’s surface that is not being illuminated by sunlight. Use Figure 2.1 to answer the questions in the lab report section. p. 6 Figure 2.1 (Note from the positions above, A-E, New Moon and Full Moon are not given) B. Exercise 2: In the blank boxes provided in the lab report section sketch how the Moon would appear from Earth for the four Moon position that you did not choose in Exercise 1. Be sure to label each sketch with the corresponding letter indicating the Moon’s position from Figure 2.1. C. Exercise 3: Shade in each of the four Moons drawn in Figure 3.1 to indicate which portion of the Moon’s surface will not be illuminated by sunlight (use color to indicate darkness). Answer the questions in the lab report section. D. Exercise 4: Consider the following debate between two students about the cause of the phases of the Moon and answer the question in the lab report section: Student 1: The phase of the Moon depends on how the Moon, Sun and Earth are aligned with one another. During some alignments only a small portion of the Moon’s surface will receive light from the Sun, in which case we would see a crescent moon. Student 2: I disagree. The Moon would always get the same amount of sunlight; it’s just that in some alignments Earth casts a larger shadow on the Moon. That’s why the Moon isn’t always a full moon. E. Exercise 5: Answer the questions in the lab report section. p. 7 F. Exercise 6: Use Figure 2.2 to answer the questions in the lab report section Figure 2.2 2.2 Moon Topography Using a Moon Globe, find the craters, maria and mountains described in the Table 3.1, and fill in the table with the lunar latitude and lunar longitude for each case (within 5 degrees). When writing a lunar latitude in Table 3.1, remember to indicate whether the position is North (N) or South (S). When writing a lunar longitude in Table 3.1, remember to indicate whether the position is East (E) or West (W). In Figure 3.2, with the aid of a Moon Globe, mark clearly each of the surface features listed in Table 3.1. Answer the questions below Table 3.1. Record your results in Part 3 - Lab Report.