The Earth, Moon, and Sun
By James Kregenow
Textbook Key Concepts:
How does Earth move in Space?
Earth moves through space in two ways: Rotation and Revolution. The spinning of Earth on its axis is called rotation. Earth completes one full rotation about every 24 hours. It is day on the side of Earth that is facing the sun, but because it rotates every day, half the day is day, and the other half is night. Revolution is the movement of on object around another. Earth revolves around the Sun, and as it does so, it follows a path, or an orbit. Earth's orbit is not a perfect circle, it is elongated, or an ellipse. Earth takes roughly one year to complete a revolution around the sun.
What causes the cycle of seasons on Earth?
Near the equator, the Sun's rays are very focused and direct year round. But in the North and South Poles, the rays are very spread out, causing very little heat energy, causing year round winters.
The seasons are caused because of the tilt of Earth's axis. In December, the North pole is tilted away from the Sun. In June, the North pole is tilted towards the Sun. In March and September, neither hemisphere is tilted towards, or away from the Sun. This happens because when Earth revolves around the Sun, the axis isn't straight up and down, it is always leaning.
A solstice is a day when the Sun is farthest North or South of the equator. An equinox is when neither hemisphere is tilted towards the Sun. Each happen twice a year: December solstice, or winter solstice (shortest day in northern hemisphere), June solstice, or summer solstice (longest day in northern hemisphere), March equinox, or Spring equinox (Days and nights are 12 hours each), and September equinox, or autumn equinox (Days and nights are 12 hours each).
What determines the strength of the force of gravity between two objects?
A force is a push or a pull, and gravity is the attractive force between objects. Newton's Law of Universal Gravitation states that every object in the universe attracts another object. Mass is the amount of matter in an object. Gravity's strength depends on the objects' masses, and the distance between them. The bigger the objects are, the higher the force of gravity, and the smaller they are, the smaller the force. The smaller the distance, the higher the force, and larger the distance, the smaller the force. If the mass of the objects are small and the distance is large, there will be a very small force of gravity. If the mass of the objects are large and the distance is small, there will be a very large force of gravity.
What two factors combine to keep the Moon and Earth in orbit?
Inertia is what keeps the Earth and Moon in orbit. Inertia is the tendency of an object to resist change in motion. Newton's first law of motion says an object at rest will stay at rest and an object in motion will stay in motion with a constant speed and direction unless acted by a force. In an orbit, there is a force, and that is gravity. There is a perfect balance between speed and gravity when an object is in orbit. If there wasn't, the object would either come closer to the object it is orbiting, or it would move in a straighter line further away, still orbiting. In both cases, though, it will keep its orbit unless it is abruptly disturbed.
What causes the phases of the moon?
The different shapes of the Moon you see from Earth are called phases. Phases are caused by the changing in relative position of the Moon, Earth, and the Sun. There are eight major phases of the moon: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, and Waning Crescent.
Waxing means growing and Waning means shrinking. The phases we see all depend on our perspective of the moon and the position of the Earth and the Moon. The Lunar Calender is dependent on the phases of the Moon. One Lunar Month is how long it takes to complete one full cycle of phases, New Moon to New Moon. One Lunar Month is almost exactly one month in the calender we use now.
What are Solar and Lunar eclipses?
An eclipse is a partial or total blocking of one object in space by another. The two types that we can see on Earth are Solar and Lunar eclipses. The word Solar comes from the word Sun, and Lunar comes from Moon, so there are Sun eclipses, and Moon eclipses. Eclipses are caused the same way as the phases of the Moon, but eclipses happen a lot less, and are rare to see. The Sun, Moon, and Earth have to line up perfectly in order for one to happen. Solar eclipses are when the Moon blocks the Sun, and The Moon casts a giant shadow on Earth. Lunar eclipses happen when it is a full Moon and Earth gets directly in between the Sun and Moon, causing Earth to cast a giant shadow on the Moon.
What causes the tides?
Tides are caused by differences in how much the Moon's gravity pulls on different parts of the Earth. Tides are the rise and fall of ocean water that occurs every 12.5 hours or so. High tides occur because the moon's gravity pulls the ocean water closer to the moon, rising the water level. On the other side of the Earth, Another high tide occurs. This happens because the Moon's gravity is also pulling the Earth itself, and it leaves behind some of the water, raising the water level. In between the two high tides on each side of the Earth, there is a low tide, where the water level is lower than average. This happens because the high tides need to get the water from somewhere to raise their water level.
What features are found on the Moon's surface?
Features on the moon's surface include maria, craters, and highlands. Maria are the dark, flat areas on the moon. Maria is the Latin word for seas because Galileo incorrectly though that the maria were oceans, but they are actually hardened rock formed from huge lava flows billions of years ago. Craters are the large round pits that are on the moon. Some of them can be hundreds of kilometers wide. For a long time, scientists thought that they were formed by volcanoes, but we now know that they were caused by the impacts of meteoroids, which are chunks of rock from space. Highlands are the lightly colored portions that are easiest to see from Earth. Galileo correctly inferred that the lightly colored portions of the moon are highlands or mountains because the rims of craters, highlands, and mountains cast large shadows on the low parts of the moon, which he could see.
What are some characteristics of the Moon?
The Moon is dry and airless. Compared to Earth, the Moon is small and large variations in its surface temperature. There is no atmosphere on the Moon, so there is no oxygen to breath, and no protection from the Sun. You would need a bulky space suit that provides oxygen, and Sun block so you don't get burned. The Moon has a diameter of 3,476 kilometers, a little less than the distance across the United States. This is about a quarter of Earth's diameter. The Moon has about one-eightieth the mass as Earth. The temperature range is from 130 degrees c in the day to -180 degrees c at night because there is no atmosphere. The Moon has no liquid water, but there is evidence there might be large patches of ice near the Moon's poles. Also, there might be large ice patches in valleys in the shadow of a mountain. But even if there is water on the Moon, there would be barely enough to support a colony from Earth.
How did the Moon form?
Scientists Theorize that a planet - sized object collided with Earth to form the Moon. About 4.5 Billion years ago, The Solar System was full of rocky debris, some of them the size of planets. Material from the object and Earth's outer layers combined because of gravity, and went into orbit forming the Moon.
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