Earth, Moon, and Sun
By: Emily Cronin
Section 1: Earth in Space
How Does Earth Move in Space?
Earth moves through space in two different but both very important ways: rotation and revolution.
Rotation is the spinning of Earth on its axis. It is because Earth rotates that Earth experiences day and night. This is because as Earth rotates or turns east, the sun appears to move towards the west across the sky. It is day on the side of Earth facing the sun and night on the side facing away from it. The Earth continues to rotate to the east causing the sun to look like it is setting in the west. It takes about 24 hours for Earth to rotate once on its axis causing day and night.
Revolution is the movement of one object around another. A year consists of one revolution around the sun. It takes 365.25 days to do this. While revolving around the Sun, the Earth follows a path called an orbit. While there are many types of orbits, Earth's orbit is a elongated circle or an ellipse.
What Causes the Cycle of Seasons on Earth
The tilt of Earth's axis is what causes our seasons. As the Earth revolves around the Sun the direction in which the axis is facing changes which causes the cycle of the seasons on Earth. In June, the northern end of the axis is tilted towards the Sun causing summer in the Northern Hemisphere and winter in the Southern Hemisphere. In March and September neither end of the axis is tilted towards the sun resulting in each hemisphere receiving the same amount of energy. In December, the south end of the axis is tilted towards the Sun resulting in summer in the Southern Hemisphere and winter in the Northern Hemisphere.
Solstices are the day when the sun is farthest north or south of the equator. The day when it is farthest north is the summer solstice, June 21, in the northern hemisphere. The day when it is the farthest south is the winter solstice, December 21, in the northern hemisphere.
Equinoxes are the days when neither hemisphere is tilted towards the sun. This results in days of equal day and night hours. There are two equinoxes per year on Earth. The spring or vernal equinox is on March 21st and the autumnal or fall equinox is on September 22nd.
Section 2: Gravity and Motion
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 major factors. They are the masses of the objects and the distance between them. This force is measured in units called newtons. They were named after Sir Isaac Newton who made tremendous strides in the field of gravity throughout his life one being creating the law of universal gravitation which states that every object in the universe attracts every other object.
What Two Factors combine to Keep the Moon and Earth in Orbit?
The two factors that combined keep the Moon and Earth in orbit are inertia and gravity.
Inertia is the tendency of an object to resist a change in motion. The greater the mass an object has, the greater the inertia. This is why an object with greater inertia is more difficult to start or stop. Sir Isaac Newton took his ideas about inertia and created the first law of motion which states that an object at rest stays at rest and an object in motion stays in motion with a constant speed and direction unless acted on by a force.
Inertia and gravity work together to keep the Moon and the Earth in their orbits. For example, Earth's gravity is constantly pulling the moon towards it, preventing the moon from traveling in a strait line. At the same time, the moon is constantly moving forwards because of inertia. If not for the Earth's gravity, inertia would cause the moon to move away into space at a straight line. it is the same with the Earth and the Sun.
Section 3: Phases, Eclipses, and Tides
What Causes the Phases of the Moon?
Phases are the different shapes of the moon you see from Earth. In one revolution around the Earth, the moon completes the cycle of phases. The changes in the relative positions of the moon, Earth, and Sun cause the phases of the moon. Sun is always reflecting light off the Moon resulting in half of the moon almost always being in sunlight. However, because the moon revolves around the Earth, you see the moon from different angles. You see half of the moon, but that half is not always in sunlight. The phase of the moon you can see is dependent upon how much of the sunlit side of the moon faces the Earth.
What are Solar and Lunar Eclipses?
Eclipses are partial or total blocking of one object in space by another. When the moon's shadow hits Earth or Earth's shadow hits the moon, an eclipse occurs. In the same way when the an object in space comes between the sun and a third object, it casts a shadow on that object resulting in an eclipse. There are two major types of eclipses: solar and lunar. The word solar derives from the Latin word for sun and the word lunar derives from the Latin word for moon. Thus, resulting in solar eclipses when the object crosses the sun and casts a shadow and lunar eclipses when the object crosses the moon and casts a shadow.
What Causes the Tides?
Tides are the rise and falls of ocean water that occurs about every 12.5 hours. Tides are caused by differences in how much the moon's gravity pulls on different parts of Earth. If a location is close to the moon, then the gravitational pull from the moon will be higher than the gravitational pull on the Earth as a whole resulting in a high tide. on the opposite side of the Earth there is a gravitational pull that is weaker than that on the whole Earth. The Earth is being pulled farther towards the Moon than the water resulting in the water being left behind creating a high tide. The land between the two locations have their water being pulled away from them by the two locations resulting in low tides. At any time there are two places with high tides and two places with low tides on Earth.
Section 4: Earth's Moon
What Features are Found on the Moon's Surface?
The features on the moon's surface include maria, craters, and highlands.
Maria are the dark, flat areas on the moon. The word maria derives from the Latin word for seas. These "seas" were named by Galileo. However, Galileo thought that the maria were oceans, but they really are hardened rock that formed from large lava flows that occurred around 3 to 4 billion years ago.
Craters are large round pits on the moon's surface. They were named also by Galileo. For a long time, scientists thought hat these craters had been made by volcanoes like the maria. However, scientists now know that these craters were caused by the impacts of meteoroids, chunks of rock and or dust from space. Although craters are located all over the moon, the maria have very few compared to surrounding areas. This means that a large amount of the craters were formed from impacts early in the moon's history before the maria formed. On Earth, these ancient craters have long disappeared. They were worn away over time by forces such as water and wind. Since the moon has no liquid water or an atmosphere, its surface has not changed very much over its long existence.
Highlands are mountains on the moon's surface. Galileo correctly thought that some of the light colored areas and features of the moon's surface were highlands. The peaks of the highlands and the area around the craters, rims, made dark shadows that Galileo could see from Earth. These highlands cover much of the moon's surface.
Come join me at the NASA Space Center to go on a trip of a lifetime to the moon. On this trip you will have the opportunity to see all of the wondrous land forms on the moon.
Directions to the Space Center are posted below on a map.
What are Some Characteristics of the Moon?
There are many ways to characterize the moon. Some of these ways include size and density, temperature and atmosphere, and water. The moon is very dry and it has no air. When compared to the Earth, the moon is small and has large variations in its surface temperatures.
Size and Density - The moon is 3,476 kilometers in diameter which is slightly less then the distance across the United States which is about one fourth Earth's diameter. Even though it is about one fourth of the Earth in size, the moon's density is only about one eightieth the amount on Earth. Earth's core is a very dense. However, as you come closer to Earth's surface the density decreases. In comparison the moon's density is almost equal to the density of Earth's surface levels.
Temperature and Atmosphere - The temperature on the moon's surface ranges from a very warm 130 degrees Celsius in direct sunlight to a very cold -180 degrees Celsius at night. These large temperature differences are a result of the almost non-existent atmosphere on the moon. The moon's gravity force is so weak that the gases can easily escape into the surrounding space.
Water - The moon as no liquid water. There is evidence that the moon has large patches of ice near its poles, though. Some of the moon is shielded from sunlight by crater walls resulting in these areas to have temperatures that are low enough for ice to form and remain frozen. In the future, if there was a colony built on the moon, any of this water would be scarce and valuable. This is because it would be very expensive to transport large amount of water from Earth to the moon.
How Did the Moon Form?
Over the years there have been many possible theories about how the moon was formed. For example, the moon could have been formed elsewhere in the solar system and been captured by Earth's gravity as it came by the planet. It is also unknown to scientists whether the moon was formed at the same time as the Earth and at the same place as the Earth. Through research scientists have found reasons to reject each of these theories. The theory that is most probable is the collision-ring theory. Around 4.5 billion years ago, the solar system was filled with rocky debris some of which were the size of small planets. Scientists theorize that a planet-size object collided with the Earth to form the moon. Some materials from the object and Earth's outer layers was ejected into orbit around the Earth, where it then formed a ring. Gravity caused this material to combine to form the moon.