Stars and Galaxies
Chapter 25
Section 1
The Study of
Stars
Objectives:
Describe the electromagnetic spectrum
Explain how reflecting and refracting
telescopes work
Compare and Contrast optical telescopes
and spectroscopes
Infer the relationship between the
frequency of electromagnetic waves and
their wavelength
Skills Warm-up
Star Words
Write as many words as you can to
describe stars from just observing them.
Write something you know about stars but
can’t tell by just looking at them.
Compare your words with your classmates.
Stars
Stars are swirling,
glowing balls of gas
There are >
200,000,000,000 billion
The sun is very
important to earth, but
it is just an average
star
Many other stars are
much bigger and
brighter
How are stars studied?
Electromagnetic Spectrum
All stars produce energy in the form of
electromagnetic waves:
Visible light
Radio waves
Heat
X-rays
Each type of energy has a
characteristic wavelength and frequency
Electromagnetic spectrum - all types of
electromagnetic wave energy, from very low
frequency to very high frequency
Optical Telescope
Microscopes use lenses collect visible light from
small objects and produce images that are much
larger
Optical telescopes work the same way, using lenses
or mirrors to collect visible light
The only difference is that the light comes from a
very large and distant object
It then makes the distant object look larger and
closer
Optical Telescopes
Refracting telescope –
uses lenses to collect
and focus visible light
Reflecting telescope –
uses mirrors to collect
and focus visible light
Optical Telescopes
The larger a mirror or
lens, the larger the
image it can make
But, if they get too big,
they bend from their
own weight
The telescope with the
largest single mirror (5
m in diameter) is in the
Hale Observatory in
California
Spectroscopes
A star’s visible light has a characteristic spectrum of
light of different wavelengths because each chemical
element in the star blocks particular wavelengths of
light
By looking at a star’s spectrum, scientists can figure
out what its chemical makeup is
A spectroscope contains a prism to separate the light
and a small optical telescope to see the spectrum
Stars contain ~ 75% hydrogen and 22% helium
Radio Telescopes
Collect radio waves from
space
Reflecting dish collects
waves that are reflected
to the antenna and then
amplified
Good for studying quasars
and pulsars and have
helped us learn about our
own galaxy
Activity
Work in pairs
Complete Skills Worksheet 25.1
Please hand in completed worksheet by tomorrow –
if necessary, finish for homework
Section 2
Characteristics
of Stars
Objectives:
Relate the temperature of a star to its
color
Explain how measurements of parallax are
used to measure a star’s distance from
earth
Contrast absolute magnitude and apparent
magnitude
Interpret data from an H-R diagram
Skills Warm-up
Stars in the Sky
Make a list of the sun’s characteristics.
Which of these do you think are shared by
all stars?
Which characteristics of the sun do you
think are different from other stars?
Star Classification
Scientists classify stars according
to :
Brightness
Color
Size
Mass
Color and Temperature
The color of a star is related to its temperature
Distance of Stars
Hold your finger in
front of your face.
Look at it with your
left eye closed.
Then look at it with
your right eye closed.
Does your finger seem
to move or change
position relative to the
background?
Distance of Stars
Now find an object
across the classroom
from you.
Look at it with your
left eye closed.
Then look at it with
your right eye closed.
Does this object move
position as much as
your finger did?
Distance of Stars
Parallax – apparent change in the position of an
object due to change in position of the observer
Scientists use parallax to determine the distance of a
star from earth
As earth moves around the sun, nearer stars appear
to change position relative to more distant stars
The closer a star is to earth, the greater its apparent
change of position
Measurements of change in position can be
converted into measurements of distance
Distance of Stars
Distances of stars are so great - you can’t use any
normal units of measurement
Scientists use light-years
The distance that light, travelling at a speed of
310,000 km per second, will cover in 1 year
Equal to 9.5 trillion km
Proxima Centauri – closest star to earth at 4.2
light-years
Most stars are hundreds of light-years away
Magnitude of Stars
Magnitude – brightness of stars
The brighter the star, the smaller its number of
magnitude
A star with a magnitude of -2 is brighter than one with
a magnitude of 2
Apparent magnitude – a star’s brightness from earth
Doesn’t really tell you how much light is given off
Absolute magnitude – actual brightness of a star
from a standard distance
Hertzsprung-Russell Diagram
Two scientists graphed a large number of stars based
on their absolute magnitude (luminosity) and
temperature
4 Types of Stars:
Main Sequence – stars grouped in a diagonal band
from hot/bright to cool/dim
Supergiants – very bright stars that range from cool to
medium/hot
Red giants – medium bright but cool
White dwarfs – low magnitude but relatively hot
Activity
Work in pairs
Complete Skills Worksheet 25.2
Please hand in completed worksheet by tomorrow –
if necessary, finish for homework
Section 3
Life Cycles of Stars
Objectives:
Explain how stars come into being
Describe the stages of a star’s lifecycle
Contrast the different ways in which highmass and low-mass stars end their life
cycles
Predict what will happen for the rest of the
sun’s lifecycle
Skills Warm-up
The Life of Stars
List and describe each stage of the human
life cycle.
How do you think the human life cycle is
different from that of a star?
Star Lifecycle
Human life cycle lasts about 75 years
Born
Infant
Toddler
Child
Teenager
Adult
Senior citizen
Star Lifecycle
Stars are also born,
then change and
eventually die
Star life cycle lasts
billions of years
Stars in the sky are at
different stages
Our sun is about ½ way
through its 10 billion
year life cycle
Birth of a Star
Nebula – a cloud of gas and
dust where stars are born
Made of mostly hydrogen
with helium and dust
Gravity causes the spread
out particles of matter to
condense
Matter starts to heat up and
becomes a protostar
Protostars don’t shine, but
give off infrared energy
Eventually they become hot
enough for fusion to occur
and a star is born
Low Mass-Stars – mass is less
than 5X that of the sun
Low-Mass Star Lifecycle:
Begins as a main-sequence star but gradually the
supply of hydrogen is changed by fusion into helium
Red Giant stage –
core of star starts to collapse
becomes hotter and denser
helium is converted to carbon
short part of life cycle
Dwarf stage –
Star cools and collapses inward to be a white dwarf
Eventually no light is given off and is a black dwarf
High Mass-Stars – mass is more
than 6X that of the sun
High-Mass Star Lifecycle:
Uses up hydrogen at a much faster rate
Supergiant stage –
Hydrogen runs out
Core collapses
Outer layers expand greatly
Supernova stage –
Pressure builds up and cause a massive explosion
When only tiny core of neutrons remains it becomes Neutron star – dense core of neutrons
Black hole – so dense and gravity so strong nothing can
escape it
Activity
Work in pairs
Complete Skills Worksheet 25.3
Please hand in completed worksheet by tomorrow –
if necessary, finish for homework
Section 4
Galaxies and Star
Groups
Objectives:
Describe the 4 types of galaxies
Explain what a constellation is and how it
differs from a galaxy or star cluster
Explain how scientists know the universe is
expanding
Predict how the constellations will look in
the distant future
Skills Warm-up
Lions and Tigers and …..
When you look at the sky on a clear night,
what shapes do the stars make?
Draw what they look like to you.
Galaxies
Galaxy – collection
of stars, nebulae,
gases, dust, and
planets that move
through space as a
unit – held together
by gravity
There are at least 10
billion galaxies in
the universe – ours
is the Milky Way
Types of Galaxies
Spiral – flat disk with a
bulge in the middle
Have long spiral arms
that swing out and
rotate like a pinwheel
Contain large amounts
of gas and dust
Example – Milky Way
Types of Galaxies
Barred Spiral – similar to
spiral but arms are attached
to a straight bar shape
Bar is much brighter and
denser than the arms
Less common than spiral
Example – Sculptor Galaxy
Types of Galaxies
Elliptical – football
shaped
Rotate differently
than spirals – more
slowly
Contain less gas and
dust
Example – Maffei 1
Types of Galaxies
Irregular – don’t
have regular shapes
Vary greatly in size
Least common type
Example – Small
Magellanic Cloud
Constellations
Star patterns shaped like
people, animals, or objects
There are 88 official
constellations
The stars in constellations may
look like they are close
together from earth, but they
are not
Constellations are important
because
They help form a map of the
sky
Locations are described in
relation to constellations
Stars are named by which
constellation they are in
Expansion of the Universe
Big Bang Theory :
15 – 20 million years ago all
matter in the universe was
packed into one giant
fireball
The fireball exploded,
spreading matter and energy
out in all directions
As matter cooled, the force
of gravity pulled together
the particles of matter to
form stars and galaxies
The universe was born!!!
Expansion of the Universe
What’s the proof???
The Doppler Effect
The light waves from an object
moving away from earth are
spaced more widely apart than if
it were standing still
The waves appear to have a
longer wavelength than they
really have and shift to the red
end of the visible light spectrum
All other galaxies have a red shift
in their spectrums which means
they are moving away from earth
Doppler Effect Video
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wfp=1
Beyond the Solar System
Do you think that reaching other
stars may some day be
possible??????
Problems:
Distance – a spaceship travelling
at the speed of light would take
over 8 years to make a round
trip to the nearest star
Technology – we don’t have a
spaceship that can travel
anywhere near the speed of
light
Space probes – it would be
difficult for people to travel, so
scientists are looking to send
data collecting devices instead
Activity
Work in pairs
Read Unit 9: The Milky Way Galaxy and Beyond
Complete attached worksheet “Quick Check”
Please hand in by tomorrow – if necessary, finish for
homework
Debate
I will split the class into 2 teams and assign which side of an issue
your team will be arguing on.
Take ½ of the class period with your team to come up with
arguments to support your part of the issue.
Pick 4 representatives from each team to debate against the
opposing team.
Issue:
Is space exploration worth the cost????
How valuable is more knowledge about the universe?
What could be done with the money that is currently being used for
space exploration?
Debate Rules
Introduction:
Team A will introduce their side of the issue with an
opening statement and their supporting argument
Team B will introduce their side of the issue with an
opening statement and their supporting argument
Rebuttal:
Team A will rebut team B’s argument
Team B will rebut team A’s argument
Closing:
Team A will make a closing statement
Team B will make a closing statement
Debate Rules
Use facts from handouts to support your
position
No personal attacks!!!!!!!
Only one person speaks at a time - you will
have time for rebuttal