The Solar System
• Section 1: An Overview of The Solar System
• Section 2: The 9 Planets of The Solar System
Early views of the organization of
Space were much different than ours.
Early astronomers believed that the Earth was the
center of our Universe, and that the Earth was
surrounded by a ball, called a Celestial Sphere, on
which were fixed most of the objects of the heavens.
This interpretation of our solar system is called a
Geocentric Model, meaning Earth-centered.
Early astronomers noticed groups of stars that were visible
at the same time every year. These were named
constellations, and were used as a basis for calendars.
The Orion
Constellation
Astronomers noticed that some celestial bodies
did change position relative to the constellations.
They called these “wandering stars” planets.
Notice the planet Mars moving across the constellations Gemini and
Leo over the course of 11 months.
Astronomers also noted that,
periodically, these planets which
normally moved eastward,
moved backward for a few
weeks, then resumed their path
eastward.
In 200 A.D., the Greek astronomer Ptolemy explained
this “retrograde’ motion by stating that the planets
orbited the Earth in a circle, but also orbited another
point in a circle, what he called an epicycle.
In the late 1400’s, the astronomer Copernicus
proposed what was to become known as the
Heliocentric Model.
Copernicus stated that the Sun was the center of
the Solar System, the Earth was a planet, and
that it orbited the Sun.
And, here is how he explained retrograde
motion.
Mars retrograde motion
Venus retrograde motion
In the 16th –century, the astronomer Johannes
Kepler developed three laws to describe the way in
which planets move through Space.
Kepler’s 1st Law: Planets move through Space in an
elliptical orbit, not a circular one. This causes the
distance from a planet to the Sun to vary.
Kepler’s 2nd Law: When a planet is closer
to the Sun, it moves faster. (centrifugal
force and gravity at work!)
Kepler’s 3rd Law states that the further a
planet is from the Sun the longer its period
of revolution (its year) will be.
In the 1600’s, Isaac Newton stated that a force
called gravity was causing the planets to behave
as Kepler had observed.
He stated that all objects with mass exerted a force of
attraction on other objects with mass, and that the
strength of that force is proportional to the mass of the
objects and their distances from one another.
What’s in Our Solar System?
• Our Solar System consists of a central
star (the Sun), the nine planets orbiting
the sun, moons, asteroids, comets,
meteors, interplanetary gas, dust, and
all the “space” in between them.
• The nine planets of the Solar System
are named for Greek and Roman Gods
and Goddesses.
The Sun
• The Sun’s age is about 5 billion years.
• Its energy comes from nuclear fusion (where hydrogen
is converted to helium) within its core. This energy is
released from the Sun in the form of heat and light.
• Stars are the only solar bodies that generate their own
light. Very bright planets, such as Venus and our
moon, appear bright because they are reflecting
sunlight. Remember: Stars produce light. Planets
reflect light.
• Our sun is classified as a yellow main sequence star.
A star’s temperature determines its “color.” The
coldest stars are red. The hottest stars are blue.
The Relative Size of the Planets in
the Solar System
Characteristics of Small Rocky
Planets
•
•
•
•
•
They are made up mostly of rock and metal.
They are very heavy.
They move slowly in space.
They have no rings and few moons (if any).
They have a diameter of less than 13,000 km
Mercury
• Mercury has a revolution period of 88 days. A
revolution period is the time it takes for a planet to
complete one full orbit around the sun. This is also
called a year.
• Mercury has extreme temperature fluctuations,
ranging from 800F (daytime) to -270F (nighttime).
• Even though it is the closest planet to the sun,
recent radar info suggests there is ICE on Mercury!
Scientists believe the ice is protected from the
sun’s heat by crater shadows. It is covered with
meteorite impacts and barely has a trace of an
atmosphere.
Venus
• Venus is the brightest object in the sky after the
sun and moon because its atmosphere reflects
sunlight so well. People often mistake it for a star.
• The atmosphere of Venus has a large amount of
carbon dioxide gas. Carbon dioxide traps heat in
Venus’s atmosphere, causing the surface
temperatures to increase greatly. We call this
effect the Greenhouse Effect. Venus’s
Greenhouse Effect is so strong that its maximum
surface temperature may reach 900F.
• Venus has no moons. It has thick yellowish
clouds composed of sulfuric acid driven by fast
winds. Its surface is dry and dusty with craters,
mountains, and volcanoes.
Earth
• Earth is the only planet known to support living
organisms.
• Earth’s surface is composed of 71% water.
– Water is necessary for life on Earth.
– The oceans help maintain Earth’s stable temperatures.
– Water is a primary cause of Earth’s surface weathering.
• Earth has a distinct atmosphere.
– It helps screen harmful radiation from the sun.
– It prevents meteorites from reaching Earth’s surface.
– It traps heat to help maintain Earth’s stable temperatures.
• Earth has one moon.
Earth’s Moon
• It takes the same amount of time for the moon to rotate
once on its axis as it does for it to orbit the earth (27.3
days). Thus, the same side of the moon always faces us.
• The moon’s surface is covered in dust and rocky debris
from meteor impacts. It has no water or atmosphere. The
dark areas of the moon are called Maria (Maria is a Latin
word meaning “seas”). Maria are large craters which have
been filled by solidified lava.
• The moon reflects light from the sun onto the earth’s
surface. Sometimes the moon may appear reddish-brown
in color as the sunlight is deflected through dust in the
earth’s atmosphere.
• The moon’s gravitational effects on the earth are most
apparent in the “coming” and “going” of the tides
Mars
• Mars has permanent ice caps at its poles.
The ice caps are composed mostly of frozen
carbon dioxide (what we call “dry ice”).
• Mars has the largest volcano in our solar
system: Olympus Mons. Olympus Mons is
approximately 24 km high (15 miles).
• Atmospheric dust makes Mars’s sky pink in
color.
• Mars has two moons: Phobos and Deimos
Asteroid Belt
• Separates the Terrestrial planets from the
Gas
• Composition of Asteroids
– Rocky
Characteristics of Gas Giants
• They are made up mostly of gases
(primarily hydrogen & helium).
• They are very light for their size.
• They move quickly in space.
• They have rings and many moons.
• They have a diameter of less than
48,000 km
Jupiter
• Jupiter is the largest and most massive planet: it’s
diameter is 11 times bigger than that of the Earth’s.
Overall, Jupiter is about 318 times the size of Earth.
Jupiter is composed almost entirely of hydrogen and
helium.
• Because Jupiter rotates so quickly, it’s clouds form
belts (low-lying, relatively warm cloud layers) and
zones (bright, high-altitude, cooler cloud layers) that
encircle the planet.
• Jupiter’s characteristic Great Red Spot is an
enormous storm, consisting of a spiraling column of
clouds big enough to contain three Earths. The clouds
are colder than the surrounding areas, and so the
Saturn
• Saturn, like Jupiter, is composed almost
entirely of hydrogen and helium. Saturn is the
least dense of all the planets. In fact, Saturn’s
density is less than that of water.
• Saturn has many rings composed primarily of
ice with some ice-coated rocky particles.
Saturn’s rings are very wide (they extend
outward to about 260,000 miles from the
surface) but very thin (less than 1 mile thick).
• Saturn has 18 known moons, some of which
orbit inside the rings!
Uranus
• Uranus is tilted on its axis at 98. Because of
its strongly tilted axis of rotation, Uranus
essentially spins on its side as it orbits the
sun.
• Uranus is blue in color due to methane gas in
its atmosphere.
• Uranus has 11 dark rings surrounding it.
These rings contain some of the darkest
matter in our solar system.
• Uranus has 15 known moons, and scientists
suspect more lurk within its rings.
Neptune
• Neptune has the fastest winds on the
solar system: up to 2000 km/hr.
• Neptune is also blue in color due to
methane gas in its atmosphere.
• Neptune has a Great Dark Spot in its
atmosphere. The Great Dark Spot is a
huge storm the size of Earth.
Neither Gas or Rocky Planet
Pluto
• Pluto is the only planet not visited by spacecraft. We are
not sure of its composition. Based on current data,
scientists believe it is a small, rocky planet.
• Pluto seems to lie on its side: its equator points straight
up, and one of its poles points directly at the sun.
• Pluto has only one moon (Charon). Pluto’s moon is half
the size of Pluto itself, which is unusually large for a
moon. Because they are so close in size, sometimes
Pluto and its moon are considered to be a double planet
system.
• Pluto was located and named in 1930.
Comets
•Comets are small rock,
dust and ice objects that
orbit the Sun.
•As the comet approaches
the Sun, the ices in the
nucleus sublime to form
the coma, a dense cloud
of gas and dust particles
around the nucleus. The
coma contains water,
carbon dioxide and other
neutral gases.
Comet Tail direction
•When comets are near
the Sun, the pressure of
the Sun's radiation on the
coma blows the dust and
gas in the coma back into
a long tail or tails.
•Due to the Solar winds
the
tail always points away
from the sun. This
means as the
comet orbits back into
deep space the tail will
be leading it.
Asteroids
complex
mixtures of
metals, and
carbon and
silicon
compounds,
asteroids are
not just dull grey
lumps of
cratered rock
METEOROIDS, METEORS, METEORITES
•Meteoroids – is a rock or
icy fragment traveling in
space. (much smaller than
asteroids
•Meteors – this is what a
meteoroid is called when it
enters into Earth’s
atmosphere. Also called a
shooting star.
Meteorite – is the part of a
meteoroid that has survived
its trip through the
atmosphere and strikes
Earth’s surface.
Meteorite Types
Iron
primarily iron and nickel; similar to type M asteroids
Stony Iron
mixtures of iron and stony material like type S asteroids
Chondrite
by far the largest number of meteorites fall into this class; similar in
composition to the mantles and crusts of the terrestrial planets
Carbonaceous
Chondrite
very similar in composition to the Sun less volatiles; similar to type C
asteroids
Achondrite
similar to terrestrial basalts; the meteorites believed to have originated
on the Moon and Mars are achondrites
Solar Eclipse
Tides