Chapter 7: The Earth-Moon-Sun System Section 2: Time and SeasonsTime and Seasons Section 1: Earth in Space Section 3: Earth’s MoonEarth’s Moon

Earth is a sphere, which is a 3-dimensional round shape. But, how do we know? Earth’s Size and Shape

1.) People noticed that all objects fall straight down. 2.) Earth’s shadow on the moon is curved. 3.) People in different parts of the world see different stars. How Did They Figure out Earth was a Sphere and Not Flat? Objects fall toward the center of the Earth due to gravity. If Earth were flat, objects would fall at a diagonal toward Earth’s center.

Gravity: The Reason Why Objects Fall Straight Down On Earth Gravity is the attractive force between two objects that depends on the masses of the objects and the distance between them. The object with less mass is attracted to the larger mass object. As the distance between the objects increases, the attractive force decreases. Astronomers think Earth formed by the accumulation of objects falling in towards the high mass iron and nickel core.

Earth’s Physical Properties Earth is wider through the equator than it is tall through the poles…so, it’s not a perfect sphere! The Sun is 400 times farther from Earth than the moon.

Convection currents in the molten iron deep in Earth’s core, along with Earth’s rotation, produce huge electrical currents. These electrical currents cause Earth’s magnetic field like that which surrounds a bar magnet. Earth’s Magnetic Field Earth’s Magnetic Field Video

If you used a compass to take you to the North Pole, you would not end up at the very top of the earth which is called the “Geographic North Pole.” Instead, the compass uses magnets to take you to the “Magnetic North Pole.” The magnetic poles move around the geographic poles over time, but stay within 11.5 degrees. The Magnetic North and South Poles “Wander”

Where is Earth’s Magnetic Field Found? The magnetosphere lies above the outer layers of Earth’s atmosphere. Within this magnetosphere are belts of charged particles known as the Van Allen belts. They contain thin plasma composed of protons and electrons.

The magnetosphere protects Earth from solar winds from the sun which can cause cancer! Do We Need a Magnetic Field?

Harmful Solar Winds & Beautiful Auroras The sun’s harmful solar winds release electrically charged particles that collide with particles in Earth’s atmosphere and cause them to glow. This glowing light is called the aurora. –In the northern hemisphere- Aurora Borealis –In the southern hemisphere- Aurora Australis. what are auroras?

Earth’s Movement Around the Sun The Earth orbits around the sun once every 365 days, 6 hours, and 9 minutes. This makes our year 365 and ¼ days. (6 hours is ¼ of 24 hours) So… every 4 years we have to account for that extra ¼ per year. After 4 years it would be 4/4 which = 1 more day. Leap years happen every 4 years. The one day added is “Leap Day”- February 29 th. The next leap year is Leap Year Explained Video

Earth’s Distance From the Sun Earth is 92,960,000 miles (149,600,000 km) away from the sun. The speed of light is 300,000 km/second. This means it takes 500 seconds (approx. 8 minutes) for light from the sun to reach Earth.

Earth’s Path Around the Sun The shape of Earth’s path around the sun is that of an ellipse. The name of the path is the “Ecliptic.” The sun is not located in the center of the ellipse, so the distance from Earth to sun varies during the year. Earth is closest to the sun in January- our winter. Earth is farthest from the sun in July- our summer.

Earth is Tilted The Earth’s axis is an imaginary line that runs from the North pole to the South pole. Rather than the axis standing up straight, it is actually tilted 23.5 degrees. During our summer the Earth’s northern hemisphere is tilted towards the sun. During our winter the Earth’s northern hemisphere is tilted away from the sun.

Earth’s Day and Night The Earth rotates on its tilted axis once per day. This rotation takes 23 hours and 56 minutes. Since Earth is revolving, a slight bit, around the sun while it rotates on its axis it actually does take 24 hours for the same side of Earth to face the sun again after rotating. Rotation and Revolution of Earth

Earth as a Planet Earth is the only planet known to sustain life. Earth is not hot like Venus because our oceans absorbed most of Earth’s carbon dioxide. They are, however, nearly the same size. Earth is not cold like Mars. Mars is nearly ½ the size of Earth. Mercury is very different from Earth; it has no atmosphere and is cratered like Earth’s moon.

3000 B.C., the Babylonians divided the circle into 360 parts they called degrees. The symbol for degree(º) was taken from their symbol for the sun. Earth rotates 360º in 24 hours. It rotates 15º in one hour. This is a time zone. Section 2: Measuring Time on Earth

The eastern states have sunrise before the western states. As you travel west, time decreases. For ex: California is 3 times zones away. If we are 3 pm in Michigan, California is noon. As you travel east, time increases. For ex: If it is noon in California, it is 3 pm in Michigan. Time Zones

A day is added to the time at the International Date Line. China is twelve hours ahead of us. If it is 8 am on Thursday here, it is 8 pm on Thursday there. If it is 1 pm Thursday here, it is 1 am Friday there. International Date Line

Rotation Measures Days The apparent movement of the Sun from noon one day until noon the next day is called a solar day. 24 hours A sidereal day is actually 23 hour 56 minutes and 4 seconds. The true time it takes for Earth to rotate once on its axis.

Revolution is the motion of Earth in its orbit around the Sun. The name of the path of Earth’s orbit around the Sun is the “ecliptic”. Revolution Measures Years

Seasons change because of the Earth’s 23.5 º tilt on it axis. Why do Seasons Change?

More hours of Daylight in Summer This causes 15 hours of daylight in our summer, 9 hours in winter, and 12 hours of daylight in Spring and Fall. 12 hours day and night = equinox. equi-= equal nox = night

The Sun reaches an equinox when it is directly above Earth’s equator, and the number of daylight hours equals the number of nighttime hours all over the world. Equinoxes and Solstices The solstice is the point at which the Sun reaches its greatest distance north or south of the equator the Tropic of Cancer and Tropic of Capricorn, respectively.

Section 3: Movement of the Moon It takes the moon 27.3 days to revolve around Earth. It actually takes 29.5 days because the Earth is revolving. This is a synodic month and a complete lunar phase cycle.

Revolution of the Moon It takes the moon 27.3 days to revolve around Earth. It actually takes 29.5 days because the Earth is revolving. This is a synodic month and a complete lunar phase cycle.

Rotation of the Moon The moon also takes 27.3 days to rotate on its axis. So, we always see the same side of the moon.

Tides A tide on Earth is caused by a giant wave produced by the gravitational pulls of the Sun and the Moon. This rise of sea level is called high tide. About six hours later, as the trough of the wave approaches, sea level drops, causing a low tide. The moon has more effect on our tides than the Sun because even though it is smaller it is much closer.

Spring and Neap Tide When the Moon and the Sun pull together, high tides are much higher. This is a spring tide. When the Moon and Sun pull at 90 degree angles to each other low tides are even lower. This is a neap tide.

Moonlight Moon phases are the changing appearances of the Moon as seen from Earth. The phase you see depends on the relative positions of the Moon, Earth, and the Sun.

Phases of the Moon A new moon occurs when the Moon is between Earth and the Sun. During a new moon the side of the Moon facing away from Earth is lit, but the side facing Earth is dark. So, even though the moon is there, it can’t be seen.

Waxing Phases Waxing—the lighted portion that we see appears larger each night and finally becomes a full moon. Waning—the lighted portion of the moon that we see gets smaller each night and finally becomes a new moon. (It’s there but, can’t be seen)

Waning Phases The word month is derived from the same root word as Moon.

A solar eclipse occurs when the Moon moves directly between the Sun and Earth and casts a shadow on part of Earth. Solar Eclipses The darkest portion of the Moon’s shadow is called the umbra.

Lunar Eclipses When Earth’s shadow falls on the Moon, a lunar eclipse occurs. A partial lunar eclipse occurs when only a portion of the Moon moves into Earth’s umbra.

The Moon’s Surface: Craters, Maria, and Mountains Depressions on the Moon, called craters, were formed by meteorites, asteroids, and comets impacting. The largest crater is on the moon; South Pole Aitken Basin. Ice can be found in the deep, dark craters.

Craters, Maria, and Mountains The moon used to have molten material. When craters formed, the edges got built up with debris that formed mountains. Over time, the craters filled with lava and became the dark-colored flat regions on the Moon called Maria. Repeated impacts caused a build up of debris known as regolith- Moon dust.

The Moon’s Interior The moon has a crust, that is thicker on the side facing away from Earth. It also has a mantle and a core.

Exploring the Moon The Apollo program landed on the moon and placed seismographs that picked up “moonquake” vibrations. Clementine and Lunar Prospector were also missions sent to take photographs of the moon.

Origin of the Moon: Giant Impact Theory The Moon formed about 4.6 billion years ago when a Mars-sized object collided with Earth. After colliding, the cores of the two bodies combined and settled toward the center of the larger object. Gas and other debris were thrown into orbit. The remainder condensed into a large mass, forming the Moon.