Chapter 20

The Solar System

Solar System

Solar System

Section 20-1 – Observing the Solar System

• Geocentric System: Ptolemy developed the Geocentric Theory that the Earth is at the center of the revolving planets.

• Heliocentric System: Later, during the 1500’s, Nicolaus Copernicus developed a new model, the Heliocentric System, which is the Earth and the other planets revolve around the sun.

20-1 Galileo

• Galileo lived nearly 100 years later after Copernicus. He made two discoveries supporting the Heliocentric Theory:– First, he saw four moons revolving around

around Jupiter.– Second, he saw that Venus goes through phases

similar to those of Earth’s moon.

20-1 Kepler

• Kepler discovered that the orbit of each planet is an ellipse. An ellipse is an elongated circle, or oval shape. However, he could not explain how the planets stayed in orbit.

20-1 Newton

• The English scientist Isaac Newton provided the answer. Newton concluded two factors:

– Inertia: a moving object will continue to move until a force acts to stop its motion. This tendency of a moving object to continue in a straight line or of a stationary object to remain in place is the object’s inertia.

– Gravity: the force that attracts all objects toward each other.

– Newton figured out that Earth keeps pulling the moon toward it with gravity, while the moon keeps moving ahead because of its inertia.

20-2 – The Sun

• The sun’s mass is 99.8 percent of all the mass in the solar system.

• Because the sun is so large, its gravity is strong enough to hold all of the planets and comets in orbit.

• The sun has an interior and an atmosphere. The sun is a ball of glowing gas that is about ¾ hydrogen, and ¼ helium.

The Sun

20-2 Nuclear Fusion

• The sun’s energy comes from nuclear fusion.– In the process of nuclear fusion, hydrogen atoms join

together to form helium. The temperature inside the core reaches about 15 million degrees Celsius. The energy produced by nuclear fusion, including light and heat, moves from the core through the sun’s atmosphere and into space. Some of the light and heat reaches Earth, giving Earth’s its main source of energy.

The Sun’s Makeup

20-2 The Sun’s Makeup

• The sun’s atmosphere has three layers:– The Photosphere: the inner layer of the sun’s atmosphere that

makes light. Photo=light.– The Chromosphere: At the beginning and end of a solar eclipse,

you can see a reddish glow around the photosphere. This glow comes from the middle layer of the sun’s atmosphere. Chromo=color.

– The Corona: In the middle of a total solar eclipse, the moon also blocks light from the chromosphere. At these times an even fainter layer, the corona, is visible. The corona sends out a stream of electrically charged particles called solar winds, which sometimes reaches Earth’s North and South Poles, creating rippling sheets of light in the sky called auroras.

20-2 Sun’s Features

• Features on or above the sun’s surface include:– Sunspots: areas of gas on the sun that are cooler

than the gases around them. The cooler gases give off less light, causing dark spots.

– Prominences: Reddish loops of gas.– Solar Flares: the energy heats gas on the sun to

millions of degrees Celsius, causing the gas to explode out in space.

The Sun’s Spots

Sun Prominences

Sun Flares

Solar Eclipse

20-3

The Inner Planets

Terrestrial Planets

• Mercury

• Venus

• Earth

• Mars

Mercury

• Mercury is the closest planet to the sun. The planet’s interior is probably made of iron and nickel. The side facing the sun reaches temperatures of 430 C during the day, and at night –170 C.

• Mercury has no moons.

Mercury

Venus

• Venus is similar in size to Earth. Venus rotates east to west, the opposite direction from most of the planets, this is called retrograde rotation.

Venus

Mars

• Mars is called the ‘red planet’. Its surface is covered with red dust. Mars is being investigated for life, astronomers may have found water in the form of ice. Mars also has seasons, tilted on its axis like Earth.

• Mars also has two moons – Phobos and Deimes.

Mars

Mars’ Moons

• phobos" is Greek for "fear

Mars’ Moons

• deimos" is Greek for "panic

20-4

The Outer Planet

The Four Outer Planet

• The four outer planets, called gas giants, due to their largeness and surfaces not being solid, gas balls. – Jupiter– Saturn– Uranus– Neptune

Gas Giants

• Gas grants have so much mass, they have a stronger gravitational force – this prevents their gases from escaping.

Jupiter

Jupiter – Red Spot

Jupiter

• Jupiter is the most massive planet. Its atmosphere is colorful with a Great Red Spot, which is an area of swirling clouds. Jupiter has 17 moons.

Jupiter

• Scientists have spotted what appear to be thunderheads on Jupiter bright white cumulus clouds similar to those that bring thunderstorms

on Earth

Jupiter’s Moon Io

Jupiter – Volcano Hot Spots

Saturn

Saturn

• 2nd largest planet. Saturn is the least dense planet in the Solar System. Saturn has hundreds of rings and are made of chunks of ice and rock.

• Saturn has 19 moons.

Uranus

• Uranus looks bluish because of the methane gas in its atmosphere.

• Uranus rotates from top to bottom – and has 18 moons.

Uranus

Neptune

• Neptune has 8 moons and its atmosphere contains visible clouds.

Neptune

Pluto

• Smallest planet with one moon – Charon.

• Pluto revolves around the sun only once every 248 Earth Years.

Pluto

The Planets in OrderSun

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

20-5 Comets

• Comet: called the “dirty snowball”, is about the size of an Earth mountain. Comets are chunks of ice and dust whose orbits are usually very long, narrow ellipses.

• When a comet gets to close to the sun, the ice turns to gas, releasing dust. The gas and dust form an outer layer called the coma. The inner layer of the comet is called the nucleus. The coma and the nucleus make up the comets head, which is the brightest part of the comet. Some of the gas is pushed away from the sun by the solar wind. This forms the comet’s tail.

• In 1705, Edmond Halley calculated that every 76 years the same comet would reappear. He predicted it would resurface in 1758, and when it did, it was named Halley’s comet.

Diagram of a Comet

Comet Diagram

Comet

Halley’s Comet

Tail of Halley’s Comet

20-5 Asteroids

• Between 1801 and 1807, astronomers discovered four small objects between Mars and Jupiter. Over the next 80 years, they found 300 more. These objects are called asteroids.

• Most asteroids revolve around the sun between the orbits of Mars and Jupiter. This region in the solar system is known as the asteroid belt.

Asteroids

Asteroids Vesta

20-5 Meteors

• A meteoroid is a chunk of rock or dust in space. Meteoroids usually come from comets or asteroids.

• 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.

• Meteorites are pieces of rock, made mostly of iron and nickel, that fall all over Earth, that did not burn up. Their sizes are usually extremely large, which makes it easier to identify them as meteorites than rock.

Meteors

Nasa Photo Journal

• http://photojournal.jpl.nasa.gov/index.html

Nasa Live

• http://www.nasa.gov/home/index.html?skipIntro=1