Download To the Stars - LBlackwell

Unit C: The Study of the Universe
Exploring (p. 254)
At night, all the stars that you can see are part of our home galaxy; the
Milky Way galaxy. A galaxy is a collection of hundreds of billions of stars
held together by gravity. The Hubble Space telescope is able to take
pictures of galaxies other than our own. All of these galaxies are moving
away from one another, which means the universe is expanding. The
universe is the term we use to refer to everything that physically exists; the
entirety of space and time, and all forms of matter and energy.
Chapter 7: Scientific evidence suggests that the universe began expanding
from a single point about 13.7 billion years ago.
Chapter 7.1 Space Flight to the Stars
Here is a summary of what you will learn in this section:
 Astronomy is the study of the universe and the celestial objects in it.
 The solar system is composed of the Sun, four rocky inner planets,
four gas giant planets, and other objects such as asteroids, comets,
and moons.
 An astronomical unit (AU) is a measure of distance, equal to the
average distance from the Sun to Earth. A light-year (ly) is a measure of
distance, equal to the distance light can travel in 1 year.
Key Terms
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astronomy
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astronomical unit
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big bang theory
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celestial objects
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galaxy
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light-year
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nebula
nuclear fusion
solar system
star
supernova
Looking Back in Time
Throughout history, societies have relied on the night sky for inspiration
and direction. Sitting around campfires at night triggered the imagination of
people to wander what might be out there. Stars became the subjects of
legends, myths and even gods.
Celestial objects are objects that can be seen in the sky. (Celestial = sky)
Examples: Sun, Moon, Earth, planets and comets
Astronomy is the study of the universe and the objects in it.
An astronomer is someone who studies astronomy.
Astronomers study celestial objects using powerful instruments, which
enable them to see far across the universe. Most celestial objects are so
far away from us is takes considerable time for their light to reach Earth,
when they are examined it is like going back in time!
From Earth to the Stars of the Milky Way
The solar system is the sun, together will all the planets and celestial
objects. Gravitational forces cause the planets and celestial objects to orbit
around the Sun.
The Sun and the Inner Solar System
At the centre of the solar system is the Sun, which is a star. A Star is a
shiny, hot ball of plasma, an electrically charged gas, with nuclear fusion
taking place at the core. Nuclear fusion is the process in which the nuclei
of atoms fuse together to form heavier atoms. The inner solar system
consists of the four rocky planets and their moons:
Mercury, Venus, Earth and Mars.
Measuring Distances in Space
Light year (ly) - a unit of measurement which equates to the distance that
a beam of light travels through space in 1 year. It is equal to 63 000 AU or
9000 billion km.
Astronomical Unit (AU) - the average
distance between the Sun and Earth,
about 150 million km!
The Outer Solar System
The asteroid belt, a ring of rocky debris, separates the rocky inner planets
from the gaseous planets of the outer solar system. Rocks are vary in size
from as small as a grain of sand to as large as 1000km!
Beyond the asteroid belt, are the four gaseous planets;
Jupiter, Saturn, Uranus and Neptune.
Beyond the orbit of Neptune, there are many more objects including minor
planets, moons and comets. Some objects are as far as 50 000 AU away,
but are still in the Sun's gravitational field.
Learning Checkpoint
Complete # 1-3 on p. 262
To the Stars
Alpha Centauri is the star nearest to our Sun and is approximately 4.3 light
years away. It is actually part of a system of three stars that orbit each
other. Many star systems have two stars, called a binary system. Often
the stars are so close together, they appear as a single point of light.
Even though the stars of the Centauri system are closest to Earth, they do
not appear to be the brightest in the sky. The brightest star in the night sky
is Sirius, part of the constellation Canis Major.
Exploding Stars
Stars have a life cycle like animals do. They are born, evolve and then die.
Stars are formed from large clouds of gas and dust called a nebula that
contract under gravity and heat up. When the pressure and temperature
are great enough, nuclear fusion begins and a star is born. A star typically
exists for millions or even billions of years, until the gradual build up of
heavy elements in the star's centre causes the core to collapse. When the
core collapses, the star explodes. This is called a supernova. The
remaining gas and dust will form a new nebula, from which more stars can
form.
Chapter 7.2 Galaxies
Here is a summary of what you will learn in this section:
 Galaxies contain about 200 billion stars each and usually have a super
massive black hole at their centre.
 At least 90 percent of the mass in the universe may be composed of
dark matter
 Galaxies come in many shapes including spiral, barred spiral, elliptical,
and irregular.
 Galaxies are often bound together in clusters. Clusters are often
associated with other clusters.
Key Terms:
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galaxy
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black hole
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dark matter
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star clusters
galaxy clusters
Our Solar System: A Speck in the Milky Way
Our home galaxy, the Milky Way is visible from Earth. It appears as a band
of billions of stars arcing across the night sky. The dark smudgy line along
the band is dust. The Milky Way is about 100 000 ly in diameter and about
2000 ly thick.
Properties of Galaxies
 All galaxies contain stars, planets and dust.
 Galaxies with a lot of dust have the capacity to produce more stars,
because stars are formed from dust and gases present in nebulae.
 Younger galaxies contain lots of dust, while ancient galaxies have
almost no dust because it was all used up in star making.
 Additional features of galaxies include: Black holes, dark matter and star
clusters.
Black Holes
Astronomers believe that in the center of every galaxy lies at least one,
super massive black hole. A black hole is a region of space where gravity
is so strong that nothing, not even light, can escape.
The Affect of a Black Hole:
 Stars are pulled into the hole and destroyed.
 The mass of the star adds to the black holes mass, increasing its size.
 The black hole in our galaxy has been pulling stars in for at least 7 billion
years. Currently Milky Way's black hole has a mass equal to 3 million
stars!!
Dark Matter
At least 90% of the universe may be filled with dark matter which cannot be
seen by telescopes. Dark matter is invisible because it does not interact
with light or any other kind of radiation.
How was dark matter discovered if it is invisible?
Astronomers were puzzled by the movement patterns of galaxies.
Gravitational forces were affecting galaxies, but the amount of visible
celestial objects, did not seem to be enough to cause the change.
Star Clusters
A star cluster is a concentration of stars in a relatively small region of
space. Two types of star clusters include:
 Open cluster: Contains a few hundred to a few thousand stars.
 Globular cluster: Contains hundreds of thousands of stars, drawn
together by the star's gravity in a spherical form.
Galaxy Shapes
Four galaxy shapes include spiral, barred spiral, elliptical and irregular.
Galaxy Type
Structure
Learning Checkpoint
 Do questions # 1-5 on p. 273
Formation
Galaxy Clusters
Galaxies occur in groups called galaxy clusters. Galaxy clusters are
formed as a result of the strong gravitational pull of galaxies. The Milky
Way galaxy is part of a group of 20 galaxies called the Local Group.
Questions
1.
How many stars are in the Local Group?
2.
The Local Group is part of a bigger cluster of galaxies. What is this
cluster called?
Galaxy Clusters
Can you label the 5 components of galaxy clusters? (Need Help? Refer to
page 274 in your text.)