Chap. 3 – Cycles of the Moon

1. Chap. 3 – Cycles of the Moon MONDAY Oct.17 C DAY Aim: Why does the moon go through phases? DO NOW: Define the following words using your textbooks: Synodic Period Sidereal Period Lunar eclipse Umbra Penumbra Total Lunar Eclipse

2. 3-1: CHANGEABLE MOON • - Looking at the moon every night we see it following its orbit around earth and cycling through its phases

3. 3-1: CHANGEABLE MOON •  MOTION OF THE MOON • -Moon revolves counterclockwise around Earth • Moons orbit is tipped a little over 5˚ - moons path takes it slightly north and then slightly south • - Always somewhere near the ecliptic • - Moves rapidly against the background of the constellations • - As moon orbits around Earth its shape changes from night to night in a month long cycle

4. 3-1: CHANGEABLE MOON • CYCLE OF PHASES • Moon always keeps the same side facing Earth • 2. Changing shape of moon as it passes through its cycle of phases produced by sun illuminating different parts of the side of the moon you can see • 3. Orbital period of moon around Earth – sidereal period (27.32) Length of the lunar phase cycle – synodic period (29.53) • - Phases of the moon are dramatic

5. 3.1: CHANGEABLE MOON

6. 3.1: CHANGEABLE MOON • Common misconception • People think something is wrong if they see the moon during the daytime • Gibbous moon is visible in the day time (quarter and crescent moon is also but harder to see when the sub is above the horizon) • “Dark side of the moon” – No permanently dark side of the moon • - Any location on the moon has sunlight for two weeks and is in darkness for two weeks • People act up at full moon • - Statistical studies of records from schools, prisons, hospitals, and so on show no evidence

7. 3.1: CHANGEABLE MOON • Cycle of phases have been observed for billions of years • Occasionally – moon displays more complicated moods turns cooper – red in a lunar eclipse

9. 3.1: CHANGEABLE MOON • Cycle of phases have been observed for billions of years • Occasionally – moon displays more complicated moods turns cooper – red in a lunar eclipse

10. Chap. 3 – Cycles of the Moon TUESDAY Oct.18 D -DAY Aim: What causes a lunar eclipse? DO NOW: Define the following words using your textbooks: Totality Partial lunar eclipse Penumbral lunar eclipse Solar eclipse Total solar eclipse Partial solar eclipse

11. 3.2: LUNAR ECLIPSE • Earth’s Shadow • Earth’s shadow point directly away from the sun • Lunar eclipse occurs at full moon if moons path carries it through the shadow of Earth • Most full moons pass north or south of Earth’s shadow and there is no eclipse

12. 3.2: LUNAR ECLIPSE • If the moons encounters Earth’s Shadow, sunlight is cut off, and the moon grows dim • Consists of two parts • Umbra – region of total shadow • Penumbra – sunlight is dimmed but not extinguished

13. 3.2: LUNAR ECLIPSE • The umbra of Earth’s shadow is over three times longer than the distance to the moon and points directly away from the sun • When the moon’s orbit carries it through the umbra it has plenty of room to become completely immersedin shadow

14. 3.2: LUNAR ECLIPSE •  Total Lunar Eclipse • Onceor twice a year, if a full moon passes through Earth’s shadow, sunlight is cutoff, and the moon darkens in a lunareclipse • When moon is totally eclipsed it does not disappear

15. 3.2: LUNAR ECLIPSE • It receives no direct sunlight but sunlight that is bent or refracted through Earth atmosphere • During totality the eclipsed moon looks copper-red because of sunlight refracted through Earth’s atmosphere

16. 3.2: LUNAR ECLIPSE • How dim does it get? • Depends on if the Earth’s atmosphere is cloudy • Depends on the amount of dust in Earth’s atmosphere (volcanic eruptions) • If the moon’s orbit carries it through the center of the umbra

17. 3.2: LUNAR ECLIPSE • Timing depends on where the moon crosses Earth’s shadow • Crosses through the center of the umbra - maximum length • Total lunar eclipse may take nearly six hours

19. 3.2: LUNAR ECLIPSE •  Partial and Penumbral Lunar Eclipses • If the moon only grazes the umbra, the eclipse is a partial lunar eclipse • If the moon enters the shadow of the penumbra but not the umbra, the eclipse if a penumbral lunar eclipse

20. Chap. 3 – Cycles of the Moon Wednesday Oct.19 E -DAY Aim: What causes a solar eclipse? DO NOW: Define the following words • - Small-angle formula • - Path of totality • - Apogee • - Perigee • - Annular eclipse • - Photosphere • - Corona • - Chromosphere • - Prominences • - Diamond ring effect

22. 3.3: SOLAR ECLIPSE • Solar Eclipse occurs if a new moon passes between the sun and the Earth and the moon’s shadow sweeps over Earth’s surface along the path of totality • If the moon covers the disk of the sun completely, you see a total solar eclipse – inside the path of totality • If the moon covers only part of the sun you see a partial solar eclipse – just outside the path of totality • Small angle formula allows you to calculate an object’s angular diameter from its linear diameter and distance. Angular diameter of the sun is about 0.5 degrees

23. 3.3: SOLAR ECLIPSE •  Moons Shadow • To see a solar eclipse you have to be in the moon’s shadow • Consists of the umbra of total shadow and penumbra of partial shadow

24. 3.3: SOLAR ECLIPSE • When the moon is near perigee, the closest point in its orbit, its angular diameter is large enough to cover the sun’s photosphere • If the moon is near apogee, the farthest point in its orbit, it looks too small and can’t entirely cover the photosphere. • A solar eclipse occurring then would be an annular eclipse • (annular eclipse swept across the US on May 10, 1994

25. 3.3: SOLAR ECLIPSE • Features of a Solar Eclipse • Solar eclipse begins when you first see the edge of the moon approaching the sun • The moment when the edge of the penumbra sweeps over your location

26. 3.3: SOLAR ECLIPSE • During a total eclipse of the sun, the bright photosphere of the sun is covered and the fainter corona, chromosphere, and prominences become visible • Sometimes at the beginning or end of the total phase of a total solar eclipse, a small piece of the sun’s photosphere can peek out through a valley at the edge of the moon and produce the diamond ring effect

28. 3.3: SOLAR ECLIPSE • Observing an Eclipse • Common misconception • Sunlight is more dangerous during an eclipse • Looking at the sun is always dangerous and can burn the retinas of your eyes

29. 3.3: SOLAR ECLIPSE • Safest way to observe the partial phases of a solar eclipse is by pinhole projection (fig 3-12 pg 43) • Only during totality, when the photosphere is completely hidden is it safe to look at the sun directly

30. 3.3: SOLAR ECLIPSE • Solar Eclipses must occur at new moon • Lunar Eclipses must occur at full moon

31. 3.3: SOLAR ECLIPSE • Moons orbit is tipped a few degrees from the plane of the Earth’s orbit; • most new moons cross north or south of the sun, and there are no solar eclipses in those months • most full moons cross north or south of Earth’s shadow, and there are no lunar eclipses in those months

32. 3.3: SOLAR ECLIPSE • Conclusion questions: (use your notes) • Draw the positions of the Earth, sun, and moon during a full moon • Draw the positions of the Earth, sun, and moon during a new moon • Using figure 3-12 on pg. 42 and the text book describe what pinhole projection is

33. Chap. 3 – Cycles of the Moon Thursday Oct.20 F -DAY Aim: How can eclipses be predicted? DO NOW: Define the following words • Eclipse season • Nodes • Lines of nodes • Eclipse year • Saros cycle

34. 3.4: Predicting Eclipses • Making exact eclipse predictions requires a computer and proper software • Ancient astronomers could make educated guesses as to which full moonsand which new moonsmight result in an eclipse

35. 3.4: Predicting Eclipses • Reasons to reproduce their methods: • Important chapter in the history of science • Illustrate how apparently complex phenomena can be analyzed in terms of cycles • Exercise your scientific imagination and help you visualize Earth, the moon, and the sun as objects moving thorough space

36. 3.4: Predicting Eclipses •  Conditions for an Eclipse • The moon’s orbit crosses the ecliptic at two locations called nodes, and eclipses can occur only when the sun is crossing a node • During these periods, called eclipse seasons, a new moon will cause a solar eclipse and full moon will cause a lunar eclipse

37. 3.4: Predicting Eclipses • The View from Space • An eclipse season occurs each time the line of nodes points towards the sun • Since the orbit of the moon precesses, the nodes slip westward along the ecliptic, and it takes the sun only about 347 days to go from a node around the ecliptic and back to the same node • Eclipse year

38. SUMMARY QUESTIONS • Take out your moon clock and answer the following questions – review for quiz tomorrow!! • Determine the phase of the moon • The moon rises at 6 pm • The moon sets at 9 pm • What phase would be in for a lunar eclipse • What phase would the moon be in for a solar eclipse • A few days after waxing crescent

39. 3.4: Predicting Eclipses •  The Saros Cycles • Eclipses follow a pattern called the saroscycle • After one saros of 18 years and 11 1/3 days, the pattern of eclipses repeats • Some ancient astronomers knew of the saros cycle and used it to predict eclipses