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Earth, Moon, and Sun

How Earth Moves

- Earth in Space

Earth moves through space in two major ways: rotation & revolution.


Sunlight Striking Earth’s Surface

- Earth in Space

Near equator, sunlight strikes Earth’s surface more directly & is less spread out than near poles.


Seasons on Earth

- Earth in Space

Earth has seasons because it is tilted as it revolvesaround the sun.


Seasons on Earth

- Earth in Space

The height of the sun above the horizon varies with the season.


Seasons Activity

Click the Active Art button to open a browser window and access Active Art about the seasons.

- Earth in Space


What You Know

What You Learned

Using Prior KnowledgeBefore you read, write what you know about seasons on Earth in a graphic organizer like the one below. As you read, write what you learn.

1. The sun’s rays heat Earth.2. Earth has seasons.3. In the Northern Hemisphere, fall begins in September and

spring begins in March.

1. Areas where the sun hits Earth at a more direct angle are generally warmer than areas where the sun’s rays are more spread out.

2. The tilt of Earth’s axis as it moves around the sun causes seasons.

3. Around March 21 and September 22, day and night are each 12 hours long.

- Earth in Space


Gravity

- Gravity and Motion

The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them.


Gravity Versus Distance

As a rocket leaves a planet’s surface, the force of gravity between the rocket and the planet changes. Use the graph to answer the following questions.




Force of gravity on the rocket in millions of newtons and distance from the planet’s center in planetary radii

Reading Graphs:

What two variables are being graphed? In what units is each variable measured?




Four million newtons

Reading Graphs:

What is the force of gravity on the rocket at the planet’s surface?




One million newtons

Reading Graphs:

What is the force of gravity on the rocket at a distance of two units (twice the planet’s radius from its center)?




It decreases.

Making Generalizations:

In general, how does the force of gravity pulling on the rocket change as the distance between it and the planet increases?



Gravity and Inertia


Newton concluded that two factors–gravity and inertia–combine to keep the moon in orbit around Earth.


Asking QuestionsBefore you read, preview the red headings. In a graphic organizer like the one below, ask a question for each heading. As you read, write answers to your questions.

What is gravity? Gravity is the force that attracts all objects toward one another.

What is inertia? Inertia is the tendency of an object to resist a change in motion.

Question Answer



Motions of the Moon

- Phases, Eclipses, and Tides

The changing relative positions of the moon, Earth, and sun cause the phases of the moon, eclipses, and tides.

Luna: The Moon of Earth, continued

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•Phases of the Moon - The different appearances of moon due to changing relative position of Earth, sun and moon are called phases.

•Waxing and Waning - When moon is waxing, sunlit fraction we can see from Earth getting larger (light is right). When moon is waning, sunlit fraction getting smaller.


Phases of the Moon


The phase of moon you see depends on how much of the sunlit side of the moon faces Earth.

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The Moon’s Orbit


The moon’s orbit is tilted about 5 degrees relative to Earth’s orbit around the sun.

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Vocabulary Terms

Penumbra - (paene: almost & umbra: shadow) a space of partial illumination. Would see partial eclipse.

Umbra - a shaded area. Would see total eclipse.

Eclipse - the total or partial obscuring of one celestial body by another.

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Solar Eclipse


A solar eclipse occurs when the moon passes directly between Earth and the sun, blocking sunlight from parts of Earth.

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Lunar Eclipse


During a lunar eclipse, Earth blocks sunlight fromreaching the moon.

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Luna: The Moon of Earth, continued• Eclipses - When the shadow of one celestial body

falls on another, an eclipse occurs.• Solar Eclipses - During a total solar eclipse, the

disk of the moon completely covers the disk of the sun, as shown below.

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Luna: The Moon of Earth, continued• Lunar Eclipses - During lunar eclipse, moon passes

through Earth’s shadow.• The Tilted Orbit of the Moon - You don’t see a

solar & lunar eclipse every month because moon’s orbit around Earth is tilted.

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Tides


Tides occur mainly due to the difference in the force of gravity between the moon and different parts of Earth.


Spring and Neap Tides


When Earth, the sun, and the moon are in a straight line, a spring tide occurs. When the moon is at a right angle to the sun, a neap tide occurs.


Previewing VisualsPreview Figure 11. Then write two questions you have about the diagram of the phases of the moon in a graphic organizer like the one below. As you read, answer your questions.

Q. Why does the moon have phases?

A. The changing relative positions of the moon, Earth, and the sun cause the phases of the moon.

Q. Do we see different sides of the moon as the phases of the moon appear?

A. No; the same side of the moon always faces Earth.

Earth’s History



The Moon’s Surface

- Earth’s Moon

Features on the moon’s surface include maria, craters, and highlands.


The Moon’s Size

- Earth’s Moon

Moon is 3,476 km in diameter, a little less than distance across contiguous Untied States.

Moon’s SurfaceMaria - dark, flat areas, which Galileo named (Mah ree uh); he thought incorrectly that they were oceans. Actually hardened rock from huge lava flows - 3 to 4 Gya.

Craters - First accurately described by Galileo - round pits ranging in size from marble to 2,240 km in diameter (from Phoenix to Chicago), made - meteoroid impacts.

Highlands - Galileo inferred light-colored features highlands. By shadows.

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Luna: The Moon of Earth• The Surface of the Moon - surfaces of bodies that

have no atmospheres, such as moon, preserve a record of almost all of the impacts that bodies have had. Moonquakes have shown core of moon may be molten.

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The Origin of the Moon

- Earth’s Moon

Scientists theorize that a planet-sized object collided with earth to form the moon.


Main Idea

Detail Detail Detail

Identifying Main IdeasAs you read the section “The Moon’s Surface,” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea.

The moon’s surface has a variety of features such as…

Dark, flat areas called maria, which formed from huge lava flows

Large, round pits called craters, which were caused by the impact of meteoroids

Highlands, or mountains, which cover much of the moon’s surface

- Earth’s Moon


Graphic Organizer

Around the sun

revolves

Earth

On its axis

Years

rotates

causing causing

Night and day

The Beginnings of Rocket Science• About 100 years ago, Russian high school teacher Konstantin Tsiolkovsky proposed that machines called rockets could take people to outer space.

• Rocket - machine that uses escaping gas from burning fuel to move.

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The Beginnings of Rocket Science• A Boost for Modern Rocketry - While Tsiolkovsky proved scientifically that rockets could reach outer space, he never built any rockets himself.

• American physicist & inventor Robert Goddard launched the first successful liquid-fuel rocket in 1926.

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The Beginnings of Rocket Science•Goddard tested more than 150 rocket engines, by the time of WW II, Goddard’s work began to interest US military.

•Goddard’s work drew much attention because of terrifying new weapon that the German army had developed.

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From Rocket Bombs to Rocket Ships• Toward end of WW II, Nazi Germany developed new weapon known as V-2 rocket

• V-2 rocket could deliver explosives from German military bases to London—a distance of ~350 km.

• V-2 rocket developed by team led by Wernher von Braun, young Ph.D. student whose research was supported by German military.

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Rocket Bombs to Rocket Ships, continued

• 1945 - near end of war, von Braun & entire research team surrendered to advancing America army. United States thus gained 127 of best German rocket scientists.

• With this gain, rocket research in the United States boomed in the 1950s.

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• Birth of NASA - End of World War II marked beginning of Cold War, a long period of political tension between US & Soviet Union.

• Cold War was marked by an arms race & by competition in space technology.

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• In response to Soviet advances in space, U.S. government formed National Aeronautics and Space Administration, or NASA, in 1958.

• NASA combined all of rocket-development teams in US (Brain Trust). Their cooperation led to development of many rockets, including those shown on next slide.

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How Rockets Work• For Every Action . . . Newton’s third law of motion states that for every action there is an equal & opposite reaction.

• Can be demonstrated if you blow up a balloon & let it go. Air rushing backward from balloon (the action) results in forward motion of balloon (the reaction).

•Rockets work in same way. In fact, rockets were once called reaction devices.

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How Rockets Work, continued• Because exhaust gases are under extreme pressure, they exert a huge amount of force. The force that accelerates a rocket is called thrust.

• Thrust - pushing or pulling force exerted by engine of aircraft or rocket.

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How Rockets Work, continued• Because exhaust gases are under extreme pressure, they exert a huge amount of force. The force that accelerates a rocket is called thrust.

• Thrust - pushing or pulling force exerted by engine of aircraft or rocket.

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How Rockets Work, continued• You Need More Than Rocket Fuel - Rockets burn fuel to provide thrust that propels them. In order for something to burn, oxygen must be present.

• Although oxygen is plentiful at Earth’s surface, there is little or no oxygen in upper atmosphere & in outer space.

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How Rockets Work, continued•For this reason, rockets that go into outer space must carry enough oxygen with them to be able to burn their fuel.

• The space shuttles, for example, carry hundreds of thousands of gallons of liquid oxygen. This oxygen is needed to burn the shuttle’s rocket fuel.

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How Rockets Work, continued• The gravitational pull of Earth is main factor a rocket must overcome. A rocket must reach a certain velocity, or speed and direction, to orbit or escape the Earth.

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How Rockets Work, continued• Orbital Velocity and Escape Velocity - For a rocket to orbit the Earth, it must have enough thrust to reach orbital velocity.

• Orbital velocity - speed & direction a rocket must travel in order to orbit a planet or moon.

• The lowest possible speed a rocket may go and still orbit Earth is about 8 km/s (17,927 mi/h). If rocket goes any slower, it will fall back to Earth.

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The First Satellites• An artificial satellite - any human-made object placed in orbit around a body in space.

• There are many kinds of artificial satellites, including weather satellites, communications satellites, and remote-sensing satellites.

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The First Satellites, continued• In 1957, Soviets launched first artificial satellite, Sputnik 1. It orbited for 57 days before it fell back to Earth and burned up in the atmosphere.

• Two months later, Sputnik 2 carried the first living being into space—a dog named Laika.

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Choosing Your Orbit• Satellites are placed in different types of orbits. All of the early satellites were placed in low Earth orbit.

• Low Earth orbit (LEO) is an orbit less than 1,500 km above the Earth’s surface.

• A satellite in LEO moves around the Earth very quickly and can provide clear images of the Earth. However, this motion can place a satellite out of contact much of the time.

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Choosing Your Orbit, continued• Most communications and weather satellites circle the Earth in geostationary orbit.

• Geostationary orbit (GEO) is an orbit that is about 36,000 km above the Earth’s surface and in which a satellite is above a fixed spot on the equator.

• A satellite in GEO is always above the same spot on Earth. Ground stations are in continuous contact with these satellites so that communications will not be interrupted.

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Choosing Your Orbit, continued

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