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A. Technology, including telescopes and space shuttles, make the solar system easier to observe.

The ancient Greeks coined the word “planet,”which means wandering star. 
The Greeks were able to observe Mercury, Venus, Mars, Jupiter, and Saturn. 
B. The ancient Greeks believed in a geocentric model of the solar system, meaning that all the planets revolved around Earth.

C. In the early 1500s, Copernicus was the first astronomer who developed the heliocentric model of the solar system, which is proved to be true today.

The heliocentric model of the solar system states that the planets revolve around the sun. 
D. Galileo was the first astronomer to use a telescope

Galileo agreed with the heliocentric model of the solar system. 
We call it the “solar system”, not the “earth system” (b/c sun is at the center) 
E. Brahe, a late-sixteenth century astronomer, observed planetary positions for 20 years (made very accurate observations)
F. Kepler, a seventeenth century mathematician, discovered that planetary orbits are ellipses.

Ellipses are shapes resembling ovals or elongated circles. 
G. Isaac Newton saw that planets remain in orbit due to gravity and inertia.

If gravity did not exist, planets would move in straight lines due to inertia. Because gravity moves planets toward the sun, planets travel around the sun in orbits that are elliptical. 
Inertia causes a moving object to continue in a straight line or a stationary object to remain in place; the more mass an object has, the more inertia it has (an object with greater inertia is more difficult to start or stop) 
Gravity:  gravity attracts all objects toward each other; the strength of gravity depends on the masses of the objects and the distance between them 
The sun’s gravity pulls on the planets and inertia keeps them moving around (so they end up in orbit) 
I. The sun is a glowing gas ball that, like Earth, has an interior and an atmosphere. Unlike Earth, its surface is not solid.

A. All solar energy is produced from nuclear fusion.

Nuclear fusion occurs in the core of the sun. 
In nuclear fusion two hydrogen atoms fuse into one helium atom, releasing solar energy in the process. 
For nuclear fusion to occur very high temperatures must be present. 
The temperature of the sun’s core is about 15 million degrees Celsius. 
II. The three layers of the sun’s atmosphere are the photosphere, the chromosphere, and the corona (no boundaries between the layers).

A. The photosphere is the inner layer of the atmosphere of the sun.

It is the light sphere of the sun (what you see when you look at an image or photograph of the sun) 
B. The chromosphere is the middle layer of the atmosphere of the sun.

It is the color sphere that glows. 
C. The corona is the outer layer of the atmosphere of the sun.

It is the white aura surrounding the sun that is visible only during a total solar eclipse. 
Solar winds, which are electrically charged particle streams, are sent out by the corona. 
III. Sunspots, prominences, and solar flares are all features that occur on the sun’s surface.

A. Sunspots are gas areas on the sun that are cooler than the gases surrounding them (look like small, dark areas on the surface); appear darker because cooler gases don’t give off as much light as hotter gases

B. Prominences are large, looping gas masses located above the chromosphere; connect different parts of sunspot regions

C. Solar flares are explosions of hydrogen gas on the sun that reach out into outer space; occur when the gas from connecting sunspot regions explode out into space; greatly increase the solar wind from the corona

Increased solar wind particles can cause magnetic storms (this type of storm can disrupt radio, telephone, television signals; also cause electrical power problems for homes and businesses) 

I. The inner planets of the solar system are small and have rocky surfaces; called the “terrestrial planets”: Earth, Mercury, Venus, and Mars.

II. EARTH: About 70 percent of Earth is covered by water.
A. The atmosphere of Earth reaches over 100 kilometers above the surface of Earth.

Earth’s atmosphere contains the oxygen that is necessary for life. 
It also contains nitrogen, carbon dioxide, water vapor, and trace amounts of other gases. 
B. Earth is made of the rocky outer layer called the crust, the middle layer called the mantle made of hot molten rock, and the iron and nickel inner and outer core.

The inner core is solid, while the outer core is most likely liquid. 
III. MERCURY is the planet closest to the sun.
A. The size of Mercury is close to the size of Earth’s moon.

B. Mercury has no moons.

C. Space probes that have photographed Mercury’s surface show many craters and flat plains.

D. The atmosphere of Mercury is very thin.

E. The side of Mercury that faces the sun can have temperatures reaching 430° Celsius while the side away from the sun can go as low as –170° Celsius.

Has the greatest range of temperatures of all the planets 
IV. VENUS is the second planet from the sun that often shines brightly and that is very close in size to Earth (sometimes called Earth’s twin)

A. Venus has a retrograde rotation, meaning Venus rotates from east to west

This is the opposite direction from most other planets. 
The retrograde rotation of Venus probably occurred when a large object hit the planet, causing its rotation to change direction. 
Rotation takes 8 months, revolution take 7.5 months – so a “day” is longer than its “year” 
B. The atmosphere of Venus is very thick, heavy, and made of carbon dioxide.

Due to the large amount of carbon dioxide in Venus’ atmosphere, the greenhouse effect is present on this planet. 
The greenhouse effect traps heat in Venus’ atmosphere, causing its surface to become very hot (approximately 460 degrees Celsius). 
C. The space probes Venera 7 and Magellan both explored Venus.

19 spacecraft visits to this planet (more visits than any other planet) 
V. MARS is the fourth planet from the sun.
A. Due to Mars’ reddish tinge, it is often called the red planet.

B. Carbon dioxide makes up most of Mars’ atmosphere.

This planet’s atmosphere has a very low pressure. 
C. Mars’ poles
Mars has some frozen water at its north pole 
Mars’ south pole is made of frozen carbon dioxide 
D. Mars has a tilted axis, just like Earth, causing it to have different seasons.

During season changes, huge wind and dust storms blow. 
E. Many space probes have either photographed or explored Mars’ surface.

F. Mars’ two small moons are named Phobos and Deimos.


I. The outer planets of the solar system are Jupiter, Saturn, Uranus, Neptune, and Pluto.

A. Jupiter, Saturn, Uranus, and Neptune are called gas giants because their surfaces are not made of solids, but gases.

Because the gas giants have such a large amount of gas, they have very great gravitational pulls preventing their gases from escaping. Because of this, gas giants have atmospheres that are very deep. 
The atmospheres of gas giant planets are 3/4 hydrogen, about ¼ helium, with trace amounts of other gases. 
Astronomers believe that the cores of gas giants are probably made of solid materials like ice, rock, or frozen carbon dioxide. 
The outer layers of gas giant planets are made up of various gases that extend into their atmospheres. 
II. JUPITER, the largest planet, is about 300 times more than the size of Earth.

A. The atmosphere of Jupiter, made up of hydrogen and helium, has many thick, colorful cloud swirls.

Jupiter’s cloud swirls make up Jupiter’s Great Red Spot. 
B. Jupiter has a total of 17 moons – all very different from each other

Io is home to a great number of volcanoes; the surfaces of Ganymede and Callisto are covered with ice and craters. 
III. SATURN is the solar system’s second-largest planet.
A. Saturn’s atmosphere is very thick, filled with hydrogen and helium.

B. Rings made of ice and rock chunks surround Saturn; have their own orbit

Each ring is actually dozens of rings (there are hundreds total) 
C. Titan is the largest of Saturn’s moons

Atmosphere is so thick that little light can get through it 
IV. URANUS is a gas giant that is smaller than Jupiter and Saturn; Uranus is also much farther from the sun than Saturn, so it is much colder.

A. Uranus looks blue because of the methane gas in its atmosphere.

B. The astronomer William Herschel discovered Uranus in 1781.

C. Uranus is tilted at a 90° angle on its axis, probably due to a celestial object that knocked it on its side long ago (rotates from top to bottom instead of side to side)

D. Voyager 2 was a space probe that explored and photographed Uranus revealing that Uranus has 18 moons.

The moons have icy, cratered surfaces (craters resulted from being hit by rocks from space); also have evidence of lava flows (showing material has erupted from inside each moon) 
V. NEPTUNE, the eighth planet from the sun, is about the size of Uranus.

A. Unlike Uranus, Neptune’s atmosphere contains visible clouds.

B. Neptune was discovered because scientists in the 1840’s discovered that Uranus’ orbit was not following its calculated path.

The scientists hypothesized that another planet’s gravity was affecting Uranus’ orbit; that planet is Neptune. 
C. Voyager 2 photographed Neptune, revealing its Great Dark Spot, which was actually a giant storm (didn’t last long; 5 years later it was gone)

D. Neptune has eight moons.

Neptune’s largest moon is named Triton. 
VI. PLUTO was a solid planet  (BUT IT IS NO LONGER CLASSIFIED AS ONE), unlike the other outer planets, which are gas giants.

A. Pluto’s only moon, Charon, is over ½ Pluto’s size.

B. In 1930, astronomer Clyde Tombaugh discovered Pluto.

Astronomer James Christy discovered Pluto’s moon in 1978. 
C. Astronomers do not all agree that Pluto should be called a planet.

Some astronomers think that Pluto is just the largest of thousands of celestial bodies orbiting the sun beyond Neptune. 

I. comet: chunks of ice and dust whose orbit is a long, narrow ellipse

Made up of two main parts, the head and the tail: 
HEAD:  the brightest part of the comet; made up of the nucleus (inner layer of the comet) and the coma 
TAIL:  formed by gas and dust; looks like hair 
II. asteroid:  too small and too numerous to be considered planets; revolve around the sun

asteroid belt:  located between the orbits of Mars and Jupiter 
III. meteroid: chunks of rock or dust in space; come from comets or asteroids

IV. meteor:   when a meteoroid enters Earth’s atmosphere, friction makes it burn up and produce a streak of light you see in the sky (a meteor)

V. meteorite: meteoroids that hit the Earth’s surface; this occurs because some meteoroids are so large that they do not burn up completely

o     Geocentric model vs. heliocentric model (what’s the difference?)

o     inertia

o     gravity

o     How do inertia and gravity work together to keep planets in orbit?

o     The source of the sun’s energy

o     Layers of the sun’s atmosphere

o     photosphere

o     chromosphere

o     corona

o     solar wind

o     Features on the sun

o     sunspots

o     prominences

o     solar flares

o     Inner planets

o     Mercury (very thin atmosphere, great range of temps., etc.)

o     Venus (similar in size to Earth, greenhouse effect, retrograde rotation, etc.)

o     Earth (mostly water, 3 layers, etc.)

o     Mars (“red planet”, evidence of water, seasons, etc.)

o     Outer planets

o     Gas giants (Which ones?  Features?  Made of what?)

o     Jupiter (largest, thick atmosphere, Great Red Spot, etc.)

o     Saturn (rings made of ice and rock, thick atmosphere, etc.)

o     Uranus (bluish color, cause of the 90 degree tilt, etc.)

o     Neptune (cloudy atmosphere, Great Dark Spot, etc.)

o     Pluto (Why different?  Why not a planet?)

o     comet

o     asteroid

o     asteroid belt

o     meteoroid

o     meteor

o     meteorite