Space Investigation 2

Focus Questions What causes the phases of the moon? What causes the phases of the moon? What causes solar and lunar eclipses? What causes solar and lunar eclipses?

Phases, and Eclipses The moon is Earth’s closest neighbor in space—much closer than any planet. The moon is Earth’s closest neighbor in space—much closer than any planet. In fact, the average distance from Earth to the moon is only about 30 times Earth’s diameter. In fact, the average distance from Earth to the moon is only about 30 times Earth’s diameter. Even so, the moon is very far away— 384,400 kilometers from Earth. Even so, the moon is very far away— 384,400 kilometers from Earth.

Phases and Eclipses The moon moves in space just as Earth does. The moon moves in space just as Earth does. As the moon revolves around Earth and Earth revolves around the sun, the relative positions of the moon, Earth, and sun change. As the moon revolves around Earth and Earth revolves around the sun, the relative positions of the moon, Earth, and sun change. The positions of the moon, Earth, and the sun cause the phases of the moon, eclipses, and tides The positions of the moon, Earth, and the sun cause the phases of the moon, eclipses, and tides

Motions of the Moon The moon revolves around Earth and rotates on its own axis. The moon revolves around Earth and rotates on its own axis. It takes the moon about 27.3 days to revolve around Earth. It takes the moon about 27.3 days to revolve around Earth. Like Earth’s orbit around the sun, the moon’s orbit around Earth is a flattened circle or oval shape. Like Earth’s orbit around the sun, the moon’s orbit around Earth is a flattened circle or oval shape. The moon rotates slowly on its own axis once every 27.3 days. The moon rotates slowly on its own axis once every 27.3 days.

Motions of the Moon cont. Because the moon also revolves around Earth every 27.3 days, a “day” and a “year” on the moon are the same length. Because the moon also revolves around Earth every 27.3 days, a “day” and a “year” on the moon are the same length. The same side of the moon, the “near side,” always faces Earth. The same side of the moon, the “near side,” always faces Earth. The “far side” of the moon always faces away from Earth, so you never see it from Earth. The “far side” of the moon always faces away from Earth, so you never see it from Earth.

The “Near Side” of the Moon

The “Far Side” of the Moon

Phases of the Moon On a clear night when the moon is full, the bright moonlight can keep you awake. On a clear night when the moon is full, the bright moonlight can keep you awake. But the moon does not produce the light that you see. But the moon does not produce the light that you see. Instead, it reflects light from the sun. Instead, it reflects light from the sun. When you see the moon in the sky, sometimes it appears round. When you see the moon in the sky, sometimes it appears round. Other times you see only a thin sliver, or a crescent. Other times you see only a thin sliver, or a crescent. The different shapes of the moon you see from Earth are called phases. The different shapes of the moon you see from Earth are called phases. The Earth goes through its whole set of phases each time it revolves around Earth, that is, about once a month. The Earth goes through its whole set of phases each time it revolves around Earth, that is, about once a month.

What Causes Phases? Phases are caused by changes in the relative positions of the moon, Earth, and the sun. Phases are caused by changes in the relative positions of the moon, Earth, and the sun. Because the sun lights the moon, half the moon is almost always in sunlight. Because the sun lights the moon, half the moon is almost always in sunlight. However, since the moon revolves around Earth, you see the moon from different angles. However, since the moon revolves around Earth, you see the moon from different angles.

What Causes the Phases? The half of the moon that faces Earth is not always the half that is sunlit. The half of the moon that faces Earth is not always the half that is sunlit. The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth. The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth.

Phases of the Moon New Moon: The sun lights the side of the moon facing away from Earth. The side of the moon that faces earth is dark. New Moon: The sun lights the side of the moon facing away from Earth. The side of the moon that faces earth is dark.

Phases of the Moon cont. Waxing Crescent: You see more and more of the lighted side of the moon. This is called a waxing crescent moon. Waxing Crescent: You see more and more of the lighted side of the moon. This is called a waxing crescent moon.

Phases of the Moon cont. First Quarter: You see half the lighted side of the moon. First Quarter: You see half the lighted side of the moon.

Phases of the Moon cont. Waxing Gibbous: The moon continues to wax. The moon is called gibbous. Waxing Gibbous: The moon continues to wax. The moon is called gibbous.

Phases of the Moon cont. Full Moon: You see the whole lighted side of the moon. Full Moon: You see the whole lighted side of the moon.

Phases of the Moon cont. Waning Gibbous: The fraction of the lighted side of the moon that you see gets smaller each day. Waning Gibbous: The fraction of the lighted side of the moon that you see gets smaller each day.

Phases of the Moon cont. Third Quarter: You can see half of the moon’s lighted side. Third Quarter: You can see half of the moon’s lighted side.

Phases of the Moon cont. Waning Crescent: You see a crescent again. Waning Crescent: You see a crescent again.

The Phases of the Moon

The Cycle of the Phases During the new moon, the side of the moon facing Earth is not lit. During the new moon, the side of the moon facing Earth is not lit. As the moon revolves around Earth, you see more and more of the lighted side of the moon every day, until the side of the moon you see is fully lit. As the moon revolves around Earth, you see more and more of the lighted side of the moon every day, until the side of the moon you see is fully lit. As the moon continues its orbit, you see less and less of the lighted side of the moon. As the moon continues its orbit, you see less and less of the lighted side of the moon. About 29.5 days after the last new moon, the cycle is complete, and you see a new moon again. About 29.5 days after the last new moon, the cycle is complete, and you see a new moon again.

Eclipses On rare occasions, the moon completely blocks the sun. On rare occasions, the moon completely blocks the sun. The sky grows as dark as night even in the middle of a clear day. The sky grows as dark as night even in the middle of a clear day. The air gets cool and sky becomes an eerie color. The air gets cool and sky becomes an eerie color. If you don’t know what is happening, you can become very frightened. If you don’t know what is happening, you can become very frightened.

Eclipses cont. The moon doesn’t usually go directly between Earth and the sun or directly behind Earth. The moon doesn’t usually go directly between Earth and the sun or directly behind Earth. The moon’s orbit around Earth is slightly tilted with respect to Earth’s orbit around the sun. The moon’s orbit around Earth is slightly tilted with respect to Earth’s orbit around the sun. As a result, in most month the moon revolves completely around Earth without the moon moving into Earth’s shadow or the moon’s shadow hitting Earth. As a result, in most month the moon revolves completely around Earth without the moon moving into Earth’s shadow or the moon’s shadow hitting Earth.

Eclipses cont. When the moon’s shadow hits Earth or Earth’s shadow hits the moon, an eclipse occurs. When the moon’s shadow hits Earth or Earth’s shadow hits the moon, an eclipse occurs. An eclipse occurs when an object in space comes between the sun and a third object, and casts a shadow on that object. An eclipse occurs when an object in space comes between the sun and a third object, and casts a shadow on that object. There are two types of eclipses: solar eclipses and lunar eclipses. There are two types of eclipses: solar eclipses and lunar eclipses. The words solar and lunar come from the Latin words for “sun” and “moon.” The words solar and lunar come from the Latin words for “sun” and “moon.”

Solar Eclipses During a new moon, the moon is almost exactly between Earth and the sun. During a new moon, the moon is almost exactly between Earth and the sun. But most months, as you have seen, the moon travels a little above or below the sun in the sky. But most months, as you have seen, the moon travels a little above or below the sun in the sky. A solar eclipse occurs when the moon passes between Earth and the sun, blocking the sunlight from reaching Earth. A solar eclipse occurs when the moon passes between Earth and the sun, blocking the sunlight from reaching Earth. The moon’s shadow then hits Earth. The moon’s shadow then hits Earth. So a solar eclipse is really just a new moon in which the moon blocks your view of the sun. So a solar eclipse is really just a new moon in which the moon blocks your view of the sun.

Total Solar Eclipses The darkest part of the moon’s shadow, the umbra, is cone-shaped. The darkest part of the moon’s shadow, the umbra, is cone-shaped. From any point in the umbra, light from the sun is completely blocked by the moon. From any point in the umbra, light from the sun is completely blocked by the moon. The moon’s umbra happens to be long enough so that the point of the cone can just reach a small part of Earth’s surface. The moon’s umbra happens to be long enough so that the point of the cone can just reach a small part of Earth’s surface. Only the people within the umbra experience a total solar eclipse. Only the people within the umbra experience a total solar eclipse. During a total solar eclipse, the sky is dark. During a total solar eclipse, the sky is dark. You can see the stars and the solar corona, which is the faint outer atmosphere of the sun. You can see the stars and the solar corona, which is the faint outer atmosphere of the sun.

Total Solar Eclipse

Partial Solar Eclipse The moon casts another shadow that is less dark than the umbra. The moon casts another shadow that is less dark than the umbra. In this larger part of the shadow, called the penumbra, part of the sun is visible from Earth. In this larger part of the shadow, called the penumbra, part of the sun is visible from Earth. During a solar eclipse, people in the penumbra see only a partial eclipse. During a solar eclipse, people in the penumbra see only a partial eclipse. Since part of the sun remains visible, it is not safe to look directly at the sun during a partial solar eclipse. Since part of the sun remains visible, it is not safe to look directly at the sun during a partial solar eclipse.

Partial Solar Eclipse

Lunar Eclipses During most months, the moon goes near Earth’s shadow but not quite into it. During most months, the moon goes near Earth’s shadow but not quite into it. A lunar eclipse occurs at a full moon when Earth is directly between the moon and the sun. A lunar eclipse occurs at a full moon when Earth is directly between the moon and the sun. During a lunar eclipse, Earth blocks sunlight from reaching the moon. During a lunar eclipse, Earth blocks sunlight from reaching the moon. The moon is then in Earth’s shadow and looks dark from the Earth. The moon is then in Earth’s shadow and looks dark from the Earth. Because the moon is closest to Earth’s shadow during a full moon, lunar eclipses occur only at full moon. Because the moon is closest to Earth’s shadow during a full moon, lunar eclipses occur only at full moon.

Total Lunar Eclipse Like the moon’s shadow, Earth’s shadow has an umbra and penumbra. Like the moon’s shadow, Earth’s shadow has an umbra and penumbra. When the moon is in Earth’s umbra, you see a total lunar eclipse. When the moon is in Earth’s umbra, you see a total lunar eclipse. You can see Earth’s shadow on the moon before and after the total part of a lunar eclipse. You can see Earth’s shadow on the moon before and after the total part of a lunar eclipse. Unlike a solar eclipse, a lunar eclipse can be seen anywhere on Earth that the moon is visible. Unlike a solar eclipse, a lunar eclipse can be seen anywhere on Earth that the moon is visible. So you are more likely to see a total lunar eclipse than a total solar eclipse. So you are more likely to see a total lunar eclipse than a total solar eclipse.

Total Lunar Eclipse

Partial Lunar Eclipse For most lunar eclipses, Earth, the moon, and the sun are not quite in line, and a partial lunar eclipse results. For most lunar eclipses, Earth, the moon, and the sun are not quite in line, and a partial lunar eclipse results. A partial lunar eclipse occurs when the moon passes partly into the umbra of Earth’s shadow. A partial lunar eclipse occurs when the moon passes partly into the umbra of Earth’s shadow. The edge of the umbra appears blurry, and you can watch it pass across the moon for two or three hours. The edge of the umbra appears blurry, and you can watch it pass across the moon for two or three hours.

Partial Lunar Eclipse

Review Why does the moon change its phases as the month progresses? Why does the moon change its phases as the month progresses? Describe the relative positions of Earth, the sun, and the moon during a solar eclipse and during a lunar eclipse. Describe the relative positions of Earth, the sun, and the moon during a solar eclipse and during a lunar eclipse. Why are a “day” and a “year” on the moon the same length? Why are a “day” and a “year” on the moon the same length?