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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 Order
Sun
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?skipI
ntro=1