Explain how Earth's movement and the moon's orbit cause the phases of the moon. Explain the difference between a solar eclipse and a lunar eclipse.

Transcription

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3 Explain how Earth's movement and the moon's orbit cause the phases of the moon. Explain the difference between a solar eclipse and a lunar eclipse.

4 The Earth- Moon System Have you ever wondered why the moon seems to change throughout the month? Sometimes, the moon is a big glowing ball; other times, it's just a sliver. Since the earliest times, people have looked at the sky to learn more about the moon. They wondered about the changing appearance of the moon and noticed that the same changes happened month after month. When you look up at the moon, you see what ancient people saw. These changes in the moon's appearance are called the phases of the moon.

5 You now know that Earth rotates on its axis and revolves around the sun. But did you know that the moon rotates on its axis as it moves around Earth? Take a look at the diagram. Every 27.3 days, the moon rotates once on its axis and revolves once around Earth. The rate at which the moon rotates on its axis is the same as the rate at which the moon revolves around Earth. Because these rates are the same, the same side of the moon always faces Earth.

6 Phases of the Moon One of the most noticeable features of the moon is its continually changing appearance. When viewed from Earth over a one-month period, the moon appears to change from a fully lit circle to a thin crescent and back to a circle. This changing appearance of the moon results from the changing position of the moon in relation to Earth and the sun. As the moon revolves around Earth, the amount of sunlight reflected toward Earth by the face of the moon changes. The various appearances of the moon due to its changing position are called phases. The phases of the moon are shown in the following diagram.

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8 Waxing and Waning When the moon is waxing, the sunlit part that can be seen from Earth appears to get larger. When the moon is waning, the sunlit part seen from Earth appears to get smaller. Notice that even as the phases of the moon change, the total amount of sunlight that the moon receives remains the same. Half of the moon is always in sunlight, just as half of Earth is always in sunlight. But because the moon's rate of rotation is equal to its period of revolution, the side of the moon that is visible from Earth is always the same side.

9 As the moon moves (revolves) around the Earth, it looks like it has different shapes. The shape of the moon does not really change. It just changes its location in space.

10 Let s take a closer look at the phases of the moon. During a new moon, the moon looks dark.

11 As the surface of the moon that we see gets bigger, we say that the moon is waxing. This is a waxing crescent.

12 When the moon is ¼ of the way around the earth, it is in its first quarter phase. We see it as half lit. This is a waxing quarter moon.

13 After the quarter moon, the moon is moving towards a full moon. We call this a waxing gibbous moon. Notice that the bright part of the moon is getting larger. That s what we mean by waxing.

14 Now it s time for a full moon. The entire face of the moon that we are able to see shines during the full moon.

15 Now that the moon is ¾ of the way around the Earth, it seems to be half lit. We call this a waning quarter moon.

16 Following the full moon, the surface of the moon seems to be getting smaller. We call this a waning moon. This is a waning gibbous moon.

17 Before we get to the new moon, we see a sliver of moon shining up in the sky. This is a waning crescent.

18 Now we see a new moon again. It takes the moon about 1 month (29 ½ days) to go through the phases

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20 Eclipses An eclipse happens when the shadow of one celestial body falls on another body. A lunar eclipse happens when Earth is between the sun and the moon and Earth's shadow falls on the moon. A solar eclipse happens when the moon is between Earth and the sun and the moon's shadow falls on Earth.

21 On the left is a diagram of the positions of Earth and the moon during a solar eclipse. On the right is a picture of the sun's outer atmosphere, or corona, which is visible only when the moon appears to block the entire disk of the sun.

22 The Moon's Tilted Orbit If lunar eclipses and solar eclipses happen when Earth, the moon, and the sun are aligned, why doesn't the moon's revolution around Earth cause eclipses every month? The reason is that the moon's orbit around Earth is tilted by about 5 in relation to Earth's orbit around the sun. This tilt places the moon out of Earth's shadow for most full-moon phases. The tilt also places Earth out of the moon's shadow for most new-moon phases. Because the moon's orbit is tilted, the moon, the sun, and Earth are not aligned every month. So, eclipses do not happen every month.

23 Solar Eclipses Because the moon's orbit is elliptical, the distance between the moon and Earth changes. Types of solar eclipses: annular eclipse - the moon is at a point in its orbit that is far from Earth. In an annular eclipse, the moon does not appear to fully cover the disk of the sun some of the sun shows around the moon's edge. total solar eclipse - the moon is at a point in its orbit that is closer to Earth. During a total solar eclipse, the moon appears to be the same size as the sun and appears to fully cover the disk of the sun.

24 Lunar Eclipses During a lunar eclipse, Earth comes between the sun and the moon. Lunar eclipses can happen only during a full moon. As you can see, the moon appears to be a brightly glowing red ball during a lunar eclipse. Earth's atmosphere acts like a lens and bends some of the sunlight into Earth's shadow. When sunlight hits the particles in Earth's atmosphere, the atmosphere filters the blue light out. With the blue light removed, most of the remaining light that lights the moon is red.

25 On the left, you can see that the moon can have a reddish color during a lunar eclipse. On the right, you can see the positions of Earth and the moon during a lunar eclipse.

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27 Review: Every 27.3 days, the moon rotates once on its axis and revolves once around Earth. Earth's movement and the moon's orbit cause the phases of the moon. A solar eclipse occurs when the shadow of the moon falls on Earth. A lunar eclipse occurs when the shadow of Earth falls on the moon.