1. The Solar System
Chapter 17

2. The Solar System The center of the solar system is the sun.
Even though the sun is 150 million kilometers away it still affects the earth is many ways.
i.e. Solar Flares

3. The Solar System

4. The Solar System
Chapter 17 Section 1

5. Solar System
When you look up at the sky at night most of the objects that you see are stars.
These glowing balls of hot gas shine because they make their own light.
A few of the objects you might see are planets.
Planets are large objects in space that orbit the sun.

6. Solar System
You will likely see the earth’s moon (though there are other moons in space).
A moon is an object that orbits a planet.
It takes the earth’s moon about 29 days to complete its revolution around the earth.
From the earth we can only see one side of the moon.

7. The Moon

8. Solar System Planets and moons do not make their own light.
They shine because they reflect the light of the sun, our closest star.
Stars are the source of light for all objects in space.
The word planet comes from a Greek word meaning “wanderer.”
Because planets change their position in the sky from day to day, ancient stargazers thought of planets as wandering stars.
Planets, with their moons, revolve around the sun in what us known as the solar system.
Solar refers to the star in the center of the system: the sun.

9. Stars The stars in the night sky are not part of the solar system.
But they do move.
Stars appear to move more slowly than planets.
Why?

10. Stars A star is made mostly of hydrogen and helium gas particles.
Deep inside the star, temperatures of 15,000,000 degrees Celsius makes these particles move at incredible speeds.
When moving at high speeds, the particles collide and combine, or fuse.
This process is called fusion.
Continuous fusion produces a constant supply of energy.
This energy makes its way to the stars surface.
Gas particles on the surface become very hot and radiate light.
We see this as a shining light.

11. Stars

12. Stars Many stars are white (but not all).
Others colors include red, yellow, and blue-white.
The color of a star depends on its temperature.
This is why the sun is yellow.

13. Objects in the Solar System
The solar system contains many objects.
Nine of these objects are planets.
Each planet travels in a fixed orbit around the sun.
Most planets do not orbit in an exact circle but in an ellipse.

14. Objects in the Solar System
All planets move around the sun in the same direction.
However, the planets do not orbit together.
Each planet moves on its own path at its speed.
Mercury Orbits the fastest.
In general, the farther away a planet is from the sun, the bigger its orbit and the slower its speed.

15. Objects in the Solar System
The entire solar system holds together because of gravity.
There is gravity between every object in the solar system, attracting these objects to each other.
Because the sun has much more mass than the objects orbiting it, the objects are pulled toward the sun.
The pull of gravity is balanced by the speed and motion of the objects.
This balance keeps the objects in orbit.
Without this balance, an orbiting planet could fly off in a straight line or fall toward the sun.

16. The Sun The largest object in the solar system is the sun.
The sun is larger than all of the planets put together.
Its mass, the of matter it contains, is 99 percent of the entire solar system.
The sun is made mostly of two gases: hydrogen and helium.
Because the sun is mostly gas, it has no solid surface.

17. The Sun The sun is not fixed in space.
It rotates on an axis like a planet.
On average, the sun rotates once a month.
The sun is a star in the Milky Way Galaxy.
A galaxy is a group of billions of stars.
Galaxies are grouped their shapes.
The Milky Way Galaxy is shaped like a spiral.

18. The Milky Way

19. The Sun The outer temperature of the sun is 5,500 degrees Celsius.
This high temperature is caused by nuclear reactions inside the sun.
In the sun’s center, temperatures of 15,000,000 degrees Celsius cause hydrogen particles to fuse and form helium.
These nuclear reactions produce energy that we see as light and feel as heat.

20. The Sun The only part of the sun that can be seen is its atmosphere.
An atmosphere is an envelope of gas surrounding an object in space.
The sun’s atmosphere consists of three layers.
The inner layer is called the photosphere.
This is the layer of the gas that gives off light.
The middle layer of gas is called the chromosphere.

21. The Sun

22. The Inner Planets
Chapter 17 Section 2

23. The Inner Planets
The Planets of the solar system are divided into two groups: the inner and the outer planets.
The inner planets are the ones that are closest to the sun.
Mercury, Venus, Earth, Mars
All of the inner planets are solid and similar in size.

24. The Inner Planet

25. Mercury The planet closest to the sun is Mercury.
Because it is so close to sun it is often hard to see.
Named after the Roman god of speed, Mercury is the fastest moving planet (50 kilometers per second).
It rotates slowly though.
One day in Mercury lasts about 59 earth days.

26. Mercury The surface of Mercury is covered with craters and flat areas.
Of all the planets, Mercury’s surface temperature changes the most.
This is because Mercury has no atmosphere to hold in or keep out the sun’s heat.
The side facing the sun reaches: 427 degrees Celsius
The side facing away from the sun drops to degrees Celsius

27. Mercury

28. Venus The planet next closest to the sun is Venus.
It was named after the Roman goddess of love and beauty.
Venus is the hottest planet at 460 degrees Celsius.
It is also the brightest planet in the sky.
Because you can sometimes see Venus during the day it is known as the “morning star” or “evening star.”

29. Venus Venus rotates in the opposite direction of the other planets.
Venus takes a long time to rotate.
A day in Venus takes 243 earth days.
Venus has an atmosphere which contains large amounts of carbon dioxide.
The carbon dioxide traps the heat energy from the sun and heats up the planet’s atmosphere.
This warming process is called the greenhouse effect.

30. Venus We cannot see through Venus’s thick clouds with our eyes.
However, the spacecraft Magellan took pictures of the planet’s surface which revealed rolling plains, towering highlands, and craters.

31. Venus

32. Earth The earth is the third planet from the sun.
It is about the same size as Venus.
Several differences from the other inner planets:
Earth has a mild surface temperature that changes very little.
It has a dense, protective atmosphere.
It is the only planet to have liquid water on its surface.
Because of these unique features, the earth can support life.
The greenhouse effect also occurs on earth.
Without an atmosphere to trap heat, the Earth would be an icy planet no warmer than -10 degrees Celsius.

33. Earth

34. Mars Mars is the fourth planet from the sun.
It is named for the Roman god of war.
Mars has two small moons.
A Martian day is similar to an earth day but its year is almost twice as long as ours.

35. Mars The atmosphere on Mars is much less dense than on earth.
The atmosphere is mostly carbon dioxide.
Mars is colder than earth because it is farther from the sun and has a thinner atmosphere.
Little heat can be trapped by a thin atmosphere.

36. Mars

37. The Outer Planets
Chapter 17 Section 3

38. The Outer Planets
The outer planets have rings and are much larger than the inner planets.
The outer planets are mostly frozen gas and liquid, with a small, solid core.

39. The Outer Planets

40. Jupiter Jupiter is the largest planet in the solar system.
All of the other planets inside the solar system could fit inside Jupiter.
Jupiter was named for the Roman king of the gods.
Jupiter has colorful bands that are actually clouds of gases where storms are taking place.
The bands change shape every few days.
It only takes Jupiter 10 hours to rotate once.

41. Jupiter A large red oval appears on the surface of Jupiter.
This area is called the Great Red Spot.
The spot is actually a spinning windstorm.
It is the largest known storm in the solar system and has lasted at least 300 years.
Jupiter has rings and at least 60 moons.
Jupiter has a variety of moons: Io (active volcanoes that constantly erupt), Europa (icy world with smooth cracked surface).

42. Jupiter

43. Saturn Saturn is the sixth planet from the sun.
It was named for the Roman god of agriculture.
It is the second largest planet in the solar system.
About 1,000 rings orbit Saturn’s equator.
The rings are mostly ice particles and dust.

44. Saturn
Saturn is a giant planet of gases with stormy bands of clouds running along its surface.
Wind in these storms reaches 1,800 kilometers per hour.
One day on Saturn is 11 hours.
Saturn has at least 31 moons.
Its largest moon, Titan, is the only moon in the solar system that is known to have its own atmosphere (mostly nitrogen).

45. Saturn

46. Uranus The seventh planet from the sun is Uranus.
This planet was named for the Greek god of the sky.
Uranus tilts on its side.
It has a faint dark ring system.
Uranus has at least 11 rings and 22 moons.
A day on the planet is 17 hours long.

47. Uranus

48. Neptune Neptune is the eighth planet from the sun.
It was named after the Roman god of the sea.
It appears greenish blue because of the methane gas in the atmosphere.
It has two rings: two thin and two thick.
A day on Neptune lasts 16 hours.
Neptune has 11 moons.

49. Neptune

50. Other Objects in the Solar System
Chapter 17 Section 4

51. Asteroids
An asteroid is a rocky object smaller than a planet that has its own orbit around the sun.
Most asteroids are smaller than a kilometer wide but a few stretch to over 1,000 kilometers wide.
A large number of asteroids lie between the orbits of Mars and Jupiter.
This area is known as the asteroid belt.
It contains as many as a million asteroids.

52. Asteroid Belt

53. Asteroids Not all of these asteroids stay in their orbits.
Sometimes they are pulled out of orbit by the gravity of other planets.
When an asteroid enters the earth’s atmosphere it heats up and becomes a ball of glowing gases.
You probably know these meteors as “shooting stars.”
Many meteors occurring together is known as a “meteor shower.”
If it is big enough and does not completely burn up in the atmosphere, a meteor may hit the earth.
The part that actually strikes the earth is called a meteorite.

54. Meteor Shower

55. Comets Comets are made of ice, rock, frozen gases, and dust.
As a comet approaches the sun it warms up.
Ice turns to gas and dust is released.
The gas and dust reflect sunlight which makes it visible.

56. Comet