Download Study Guide Our Solar System Student Note: The upcoming test on

Study Guide
Our Solar System
Student Note: The upcoming test on these topics will be given on
________________. This sheet should serve as a list of main topics but it is
expected that you should also use class notes, labs and checked homework to
review as well.
Models of the Solar System

Ancient observers noticed that the positions of the stars did not change
over time. They believed that Earth was at the center of the universe.
An Earth-centered model is known as a geocentric model. In a
geocentric model, the Earth is at the center of the revolving planets and
stars.

About A.D. 140, Greek astronomer Ptolemy developed the geocentric
model. It was widely accepted for almost 1,500 years after his death.

In a heliocentric system, Earth and the other planets revolve around the
sun. In 1543, Nicolaus Copernicus further developed the heliocentric
model. Copernicus was able to work out the arrangement of the known
planets and how they move around the sun.

After years of detailed calculations, Johannes Kepler found that the orbit
of each planet is an ellipse, which is an oval shape.

For many years, people continued to believe in the geocentric model.
However, evidence collected by Galileo Galilei gradually convinced
the others that the heliocentric model was correct. In 1610, Galileo
discovered four moons orbiting Jupiter, proving that not everything in
the sky travels around the Earth. He also discovered that Venus goes
through phases similar to the moon.
Introducing the Solar System

Our solar system consists of the sun, the planets, their moons and a
variety of smaller objects. The sun is at the center with other objects
orbiting it. Gravity holds the solar system together. About 99.85% of the
mass of the solar system is contained within the sun.

Distances in the solar system are so large that they are measured in
astronomical units. One astronomical unit (AU) equals the average
distance between the Earth and the sun, about 150,000,000 kilometers.

A planet is round, orbits the sun and has cleared out the region of the
solar system along its orbit. All except Mercury or Venus have at least
one natural satellite, or moon. A dwarf planet is an object that orbits
the sun and has enough gravity to be round but has not cleared the area
of its orbit.

Scientists think the solar system formed about 4.6 billion years ago
from a cloud of hydrogen, helium, rock, ice and other materials
pulled together by gravity. Eventually, the temperature and pressure
in the cloud became so high that, through nuclear fusion, hydrogen
atoms were pressed together to form helium, a process that produces
light and heat.

Away from the sun, planets began to form as gravity pulled rock, ice and
gas together. The rock and ice form small bodies called planetismals.
Over time, planetismals collided and stuck together, eventually
combining to form all the other objects in the solar system.
The Sun

The sun has an interior and an atmosphere. The interior includes the
core, the radiation zone, and the convection zone.

The sun produces a large amount of energy in its core through nuclear
fusion, a process where hydrogen atoms join together to form helium.

The energy produced in the sun’s core moves outward through the
radiation zone. The outermost layer of the sun’s interior is called the
convection zone. In this zone, energy moves towards the sun’s surface
by convection.

Like the sun’s interior, its atmosphere is composed mainly of hydrogen
and helium. The sun’s atmosphere includes the photosphere, the
chromosphere and the corona. Each layer has unique properties.
The photosphere is the inner layer which you see when you look at the
sun. The chromosphere is the middle layer. The corona is the outer
layer. The corona gradually thins into streams of electrically charged
particles called the solar wind.

Features on or just above the sun’s surface include sunspots,
prominences, and solar flares.

Sunspots are areas of gas on the sun’s surface that are cooler than the
gases around them. Sunspots usually occur in groups. Huge looks of
gas called prominences link different parts of a sunspot region.

When loops in sunspot regions suddenly connect, they release large
amounts of magnetic energy. These eruptions are called solar flares.
The Inner Planets

The inner planets are small and dense and have rocky surfaces.
They are often called terrestrial planets.

Although the four inner planets have many features in common, they
differ in size and composition as well as distance from the sun.

Mercury is the smallest terrestrial planet and closest to the sun.
It has virtually no atmosphere because its gravity is so weak.

Venus has a thick atmosphere, an unusual pattern of rotation and
the hottest surface of any planet. It is so hot because its
atmosphere traps heat in a process called the greenhouse effect. It
rotates slowly so its day is longer than its year. Oddly, Venus rotates
from east to west, the opposite direction from most other planets and
moons.

Earth has liquid water and a suitable temperature range and
atmosphere for living things to survive. Earth has enough gravity
to hold onto most gases that make up Earth’s atmosphere. Earth is
the only planet with an oxygen-rich atmosphere. Like Venus, Earth
experiences a greenhouse effect.

Although Mars is too cold for liquid water, it does have water ice
now and had liquid water in the past. Mars’ atmosphere is more
than 95 % carbon dioxide. Some regions of the planets have giant
volcanoes.
The Outer Planets

The four outer planets are much larger and more massive than Earth
and they do not have solid surfaces. Because these four planets are so
large, they are often called gas giants. The gas giants all contain
hydrogen and helium. In addition, all have moons and are surrounded
by a set of rings. A ring is a thin disk of small particles of ice and rock.
They do not have solid surfaces. If you could visit them, you wouldn’t
have a solid place to stand.

Jupiter is the largest and most massive planet. Its mass is about 2.5
times that of all the other planets combined. One notable feature of
Jupiter’s atmosphere is its Great Red Spot, a storm that is larger than
Earth.

Saturn has the most spectacular rings of any planet. The rings are
made of chunks of ice and rock, each traveling its own orbit around
Saturn. Saturn’s largest moon, Titan, is larger than the planet Mercury
and has features that look as if they were formed by flowing liquid. A few
scientists thing that Titan might support life.

Uranus is twice as far from the Sun as Saturn, so it’s much colder. It
looks blue-green because of methane traces in its atmosphere. Its five
largest moons have icy, cratered surfaces. Uranus’s axis of rotation is
titled at an angel of about 90 degrees from the vertical. Uranus
rotates from top to bottom- not side to side.

Neptune is a cold, blue planet. Its atmosphere contains visible
clouds. Neptune’s blue color comes from methane in its atmosphere. Its
interior is hot from energy left from its formation. As the energy rises, it
produces clouds and storms in the atmosphere.
Small Solar System Objects

The solar system contains many small objects that, like the planets, orbit
the sun. Scientists classify these objects based on their sizes,
shapes, composition and orbits. The major categories include dwarf
planets, comets, asteroids and meteoroids.

Most small solar system objects are found in three areas: the asteroid
belt, the Kuiper belt and the Oort cloud. The asteroid belt is a region
between Mars and Jupiter. Beyond Neptune is a region called the
Kuiper belt, which extends to about 100 AU. Further out is the Oort
Cloud, extending more than 1000 times the distance between the sun
and Neptune.

Dwarf planets orbit the sun and have enough gravity to pull themselves
into spheres but they have other objects in the areas of their orbits.
There are five known dwarf planets, including Pluto. Except Cere, all
dwarf planets orbit beyond Neptune.

Comets are loose collections of ice, dust and small rockey particles whose
orbits can be long, narrow ellipses. Most comets originate in the Oort
cloud.

When a comet gets close to the sun, the ice melts, releasing gas and
dust. Clouds of gas and dust form a comet’s flowing, fuzzy outer layer,
or coma. The nucleus is the solid inner core of a comet. Some of the
gas and dust streams outward, forming two tails – a gas tail that points
away from the sun and a dust tail that points along the path the comet
has taken.

Asteroids are rocky objects, most of which are too small and too
numerous to be considered planets or dwarf planets. Asteroids are
leftover pieces of the early solar system that never came together to form
a planet.

Meteoroids are chunks of rock or dust smaller than asteroids. When a
meteoroid enters Earth’s atmosphere, friction with the air creates heat
and produces a streak of light called a meteor. Most meteoroids burn
up completely. But those reaching the Earth’s surface are known as
meteorites. Meteorite impacts can leave craters. Meteor showers occur
as Earth passes through areas with many meteoroids, and are often
named for the constellations from where they appear to come.