Universe Eighth Edition

1. Roger A. Freedman • William J. Kaufmann III Universe Eighth Edition CHAPTER 3 Eclipses and the Motion of the Moon

2. HW 2 – Chapter 2 Quiz DUE Friday 9/10 @ 5 PM Reading Assignment: Chapter 4 (for Monday 9/13) Exam 1: Scheduled for Wednesday 9/22 (more info later) iClickers: After today, if you forget your iClicker, you will not receive participation credit from a sign-in sheet!

4. 3-1 Why we see the Moon go through phases 3-2 Why we always see the same side of the Moon 3-3 The differences between lunar and solar eclipses 3-4 Why not all lunar eclipses are total eclipses 3-5 Why solar eclipses are visible only from certain special locations on Earth 3-6 How ancient Greek astronomers deduced the sizes of the Earth, the Moon, and the Sun By reading this chapter, you will learn

6. The phases of the Moon occur because • the Earth casts a shadow on the Moon. • the Moon casts a shadow on the Earth. • it is possible to see only part of the illuminated side of the moon depending on its position in its orbit. • of your location on Earth. • people see the Moon from different places on the Earth. Q3.2

7. The phases of the Moon occur because • the Earth casts a shadow on the Moon. • the Moon casts a shadow on the Earth. • it is possible to see only part of the illuminated side of the moon depending on its position in its orbit. • of your location on Earth. • people see the Moon from different places on the Earth. A3.2

14. If the phase of the Moon is full on the first day of spring in the northern hemisphere, where is the Moon located on the celestial sphere (see diagram)? • summer solstice • winter solstice • vernal equinox • autumnal equinox • the zenith Q3.4

15. If the phase of the Moon is full on the first day of spring in the northern hemisphere, where is the Moon located on the celestial sphere (see diagram)? • summer solstice • winter solstice • vernal equinox • autumnal equinox • the zenith A3.4

23. Why is the Moon a reddish color during a total lunar eclipse? • Lights from cities on the Earth illuminate it. • It is an optical illusion created by the eclipse. • Red light passes through the Earth’s atmosphere and then illuminates the Moon. • Light from Mars dimly illuminates the Moon. • Lunar dust reflects the sunlight. Q3.10

24. Why is the Moon a reddish color during a total lunar eclipse? • Lights from cities on the Earth illuminate it. • It is an optical illusion created by the eclipse. • Red light passes through the Earth’s atmosphere and then illuminates the Moon. • Light from Mars dimly illuminates the Moon. • Lunar dust reflects the sunlight. A3.10

33. A total solar eclipse occurs on the first day of summer in the northern hemisphere. What must be true about the Moon’s location on the celestial sphere on that day? • It must be at the vernal equinox. • It must be at the autumnal equinox. • It must be north of the celestial equator. • It must be south of the celestial equator. • None of the above. Q3.5

34. A total solar eclipse occurs on the first day of summer in the northern hemisphere. What must be true about the Moon’s location on the celestial sphere on that day? • It must be at the vernal equinox. • It must be at the autumnal equinox. • It must be north of the celestial equator. • It must be south of the celestial equator. • None of the above. A3.5

35. http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html

36. Solar eclipses only occur when the phase of the Moon is • new. • full. • first quarter. • last quarter. • waxing. Q3.8

37. Solar eclipses only occur when the phase of the Moon is • new. • full. • first quarter. • last quarter. • waxing. A3.8

42. Key Ideas • Lunar Phases: The phases of the Moon occur because light from the Moon is actually reflected sunlight. As the relative positions of the Earth, the Moon, and the Sun change, we see more or less of the illuminated half of the Moon. • Length of the Month: Two types of months are used in describing the motion of the Moon. • With respect to the stars, the Moon completes one orbit around the Earth in a sidereal month, averaging 27.32 days. • The Moon completes one cycle of phases (one orbit around the Earth with respect to the Sun) in a synodic month, averaging 29.53 days. • The Moon’s Orbit: The plane of the Moon’s orbit is tilted by about 5° from the plane of the Earth’s orbit, or ecliptic.

43. Key Ideas • The line of nodes is the line where the planes of the Moon’s orbit and the Earth’s orbit intersect. The gravitational pull of the Sun gradually shifts the orientation of the line of nodes with respect to the stars. • Conditions for Eclipses: During a lunar eclipse, the Moon passes through the Earth’s shadow. During a solar eclipse, the Earth passes through the Moon’s shadow. • Lunar eclipses occur at full moon, while solar eclipses occur at new moon. • Either type of eclipse can occur only when the Sun and Moon are both on or very near the line of nodes. If this condition is not met, the Earth’s shadow cannot fall on the Moon and the Moon’s shadow cannot fall on the Earth.

44. Key Ideas • Umbra and Penumbra: The shadow of an object has two parts: the umbra, within which the light source is completely blocked, and the penumbra, where the light source is only partially blocked. • Lunar Eclipses: Depending on the relative positions of the Sun, Moon, and Earth, lunar eclipses may be total (the Moon passes completely into the Earth’s umbra), partial (only part of the Moon passes into the Earth’s umbra), or penumbral (the Moon passes only into the Earth’s penumbra).

45. Key Ideas • Solar Eclipses: Solar eclipses may be total, partial, or annular. • During a total solar eclipse, the Moon’s umbra traces out an eclipse path over the Earth’s surface as the Earth rotates. Observers outside the eclipse path but within the penumbra see only a partial solar eclipse. • During an annular eclipse, the umbra falls short of the Earth, and the outer edge of the Sun’s disk is visible around the Moon at mid eclipse. • The Moon and Ancient Astronomers: Ancient astronomers such as Aristarchus and Eratosthenes made great progress in determining the sizes and relative distances of the Earth, the Moon, and the Sun.