Earth, Moon, and Sun
by: Tyler Mesnick
Section 1 Earth in Space
Key Concept Question #1: How does Earth move in space?
Earth moves through space in two major ways: rotation and revolution.
Earth rotates on its axis. An axis is the imaginary line that passes through Earth's center and the North and South poles. The rotation is when the Earth is spinning on its axis. Earths's rotation also causes day and night.
The Earth travels around the sun. This is called revolution. Revolution is the movement of one object around another. Earth follows a path, or orbit, as it revolves around the sun.
Key Concept Question #2: What causes the cycle of seasons on Earth?
Most places have four distinct seasons: Winter, Spring, Summer, and Autumn. The seasons have a great difference in temperature.
Earth has seasons because its axis is tilted as it revolves around the sun. Summer and Winter are caused by Earths tilt as it revolves around the sun. The Earths distance stays the same. Autumn and Spring are caused when both hemispheres receive the same amount of energy.
Section 2 Gravity and Motion
Key Concept Question #1: What determines the strength of the force of gravity between two objects?
The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them.
A force is a push or a pull. Mass is the amount of matter in an object. The force of gravity on an object is known as weight. Gravity attracts all objects toward one another. If mass increases, force also increases. If distance increases, force decreases.
Key Concept Question #2: What two factors combine to keep the moon and Earth in orbit?
Newton concluded that two factors- inertia and gravity- combine to keep Earth in orbit around the sun and the moon in orbit around Earth.
Gravity attracts all objects toward each other. Inertia is the tendency of an object to resist a change in motion. Earths gravity keeps pulling the moon toward it, preventing the moon from moving in a straight line. At the same time, the moon keeps moving ahead because of its inertia. If not for Earths gravity, inertia would cause the moon to move off through space in a straight line.
Section 3 Phases, Eclipses, and Tides
Key Concept Question #1: What causes the phases of the moon?
When the moon's shadow hits Earth or Earth's shadow hits the moon, an eclipse occurs. When an object in space comes between the sun and a third object, it casts a shadow on that object, causing an eclipse to take place.
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". A solar eclipse occurs when the moon passes directly between Earth and the sun, blocking sunlight from Earth. During a lunar eclipse, Earth blocks sunlight from reaching the moon.
Key Concept Question #2: What are solar and lunar eclipses?
The different shapes of the moon you see from Earth are called phases. The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth. The same side of the moon always faces Earth.
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. However, since the moon revolves around Earth, you see the moon from different angles. The half of the moon that faces Earth is not always the half that is sunlit.
Key Concept Question #3: What causes the tides?
The changing relative positions of the moon, Earth, and sun cause the phases of the moon, eclipses, and tides. Tides are rising and falling of ocean water that occurs every 12.5 hours or so. The water rises for about six hours, then falls for about six hours, in a regular cycle. The force of gravity pulls the moon and Earth toward each other. Tides are caused mainly by differences in how much the moon's gravity pulls on different parts of Earth. Their combined forces produce a tide with the greatest difference between consecutive low and high tides, called a spring tide. Neap tides are tides with the least difference between consecutive low and high tides. Both occur twice a month.
Section 4 Earth's Moon
Key Concept Question #1: What features are found on the moons surface?
Features on the moon's surface include maria, craters, and highlands. The moon's surface has dark, flat areas, which Galileo called maria. Maria is the Latin word for "seas".Galileo saw that the moon's surface is marked by large round pits called craters. Scientists now know that these craters were caused by the impacts of meteoroids, chunks of rock or dust from space. Galileo correctly inferred that some of the light-colored features he saw on the moon's surface were highlands, or mountains. The peaks of the lunar highlands and the rims of the craters cast dark shadows, which Galileo could see. The rugged lunar highlands cover much of the moon's surface.
Key Concept Question #2: What are some characteristics of the moon?
The moon is dry and airless. Compared to Earth, the moon is small and has large variations in its surface temperature. The moon is 3,476 kilometers in diameter, a little less than the distance across the United States. This is about one-fourth Earth's diameter. On the moon's surface, temperatures range from a torrid 130 degrees Celsius in direct sunlight to a frigid -180 degrees Celsius at night. The moon has no liquid water. However, there is evidence that there may be large patches of ice near the moon's poles.
Key Concept Question #3: How did the moon form?
The theory of the moon's origin that seems to best fit the evidence is called the collision-ring theory. About 4.5 billion years ago, when Earth was very young, the solar system was full of rocky debris. Some of this debris was the size of small planets. Scientists theorize that a planet-sized object collided with Earth to form the moon. Material from the object and Earth's outer layers was ejected into orbit around Earth, where it formed a ring. Gravity caused this material to combine to form the moon.