Download Stars - Mrs. Tosh`s class

Bell work
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What are stars made of ?
How do stars differ from one another?
Do stars move?
Write your answers in your science journal.
Then, after you have completed this section,
review your responses and change them if
necessary.
Stars
Objectives for today!
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Describe how color indicates the temperature of a
star
Explain how a scientist can identify a star’s
composition
Describe how scientists classify stars.
Describe different types of stars.
Describe the quantities that are plotted in the H-R
diagram.
Explain how stars at different stages in their life cycle
appear on the H-R diagram.
Twinkle, Twinkle little star, how I
wonder what you are?
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Most stars look like faint dots of light in the
night sky.
But stars are actually huge, hot, bright balls of
gas that are trillions of kilometers away from
Earth.
Twinkle, Twinkle little star, how I
wonder what you are?
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A star is made up of different elements in the
form of gases.
The inner layers of a star are very dense and hot.
But the outer layers of a star, or a star's
atmosphere, are made up of cool gases.
Blue is hot and red is not?
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Although red and yellow
may be thought of as
"warm" colors
blue may be thought of
as a "cool" color,
scientists consider red
and yellow to be cool
colors and blue to be a
warm color.
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example, the blue flame of the Bunsen burner is much
hotter than the yellow flame of the candle.
How bright are stars?
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The brightness of a light or star is called apparent
magnitude.
The closer a star is the brighter it may appear.
Astronomers use a star's apparent magnitude and its
distance from Earth to calculate its absolute magnitude.
Absolute magnitude is the actual brightness of a star.
If all stars were the same distance away, their absolute
magnitudes would be the same as their apparent
magnitudes.
Variable star- a star whose brightness appears to change
1. Absolute vs. Apparent
Magnitude
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1.
2.
3.
Variables which affect a
star’s brightness:
Star size
Distance from Earth
Star temperature
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Apparent magnitude:
The amount of light
received on Earth from a
star.
Absolute magnitude:
How large and hot a star
actually is in relation to
other stars.
Star Brightness
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Example: (Fig. 20.1)
Sirius has a greater
apparent brightness then
Rigel, even though Rigel
is a much hotter and
brighter star.
Why?
Sirius is closer to Earth!
Scientists classify stars by temperature and
brightness.
Objectives for today!
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Describe how color indicates the temperature of a
star
Explain how a scientist can identify a star’s
composition
Describe how scientists classify stars.
Describe different types of stars.
Describe the quantities that are plotted in the H-R
diagram.
Explain how stars at different stages in their life cycle
appear on the H-R diagram.
A. The Sun and You
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Our sun is a main
sequence star
according to the HR Diagram.
The actual brightness
is average for a star
of its average size.
2. Layers of the Sun (Fig. 20.9)
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Dense inner core which
is the site of hydrogen
fusion.
Radiation zone: Energy
bounces back and forth
before escaping.
Convections zone:
Cooler layer of gas that
is constantly rising and
sinking.
Anatomy of Sun
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Photosphere: Bright
source of much of
the light we see.
Chromosphere:
Active layer which is
home to many
significant displays.
Anatomy of Sun
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Corona: Outer layer
which is a gradual
boundary between
sun and space.
3. Sunspots
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Sunspots: Cool dark
areas on the sun’s
surface.
-First discovered by
Galileo
-Not permanent
features—Will appear
and disappear
4. Prominences and Flares
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Prominence: A huge
arching column of gas.
4. Prominences and Flares
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Solar Flares: Violent
eruptions near a sunspot
which suddenly brighten
and shoot outward at
high speed.
Distance to stars
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Because stars are so far away, astronomers use
light-years to measure the distances from Earth
to the stars.
A light-year is the distance that light travels in
one year.
Light-year: (Equal to about 9.5 trillion
kilometers)
Light-Years
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It is easier to give the distance to the North Star
as 431 light-years than as 4,080,000,000,000,000
km.
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Approximate distances:
-Sun to edge of solar system = 5.5 light hours
-Nearest star (Alpha Centauri) = 4.3 light years
-Center to edge of Milky Way = 50,000 light
years
Objectives for today!
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Describe how color indicates the temperature of a
star
Explain how a scientist can identify a star’s
composition
Describe how scientists classify stars.
Describe different types of stars.
Describe the quantities that are plotted in the H-R
diagram.
Explain how stars at different stages in their life cycle
appear on the H-R diagram.
Life cycle of Stars
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There are two paths that stars can take, based on
their mass.
The 1st is for low and medium mass stars.
The 2nd for high mass stars.
st
1
All stars start as nebulas
A cloud in space
Made of gas and dust
Can have stars inside
Most of the ones we see are inside our Milky Way
Galaxy
Large, massive, bright nebulae
Emission Nebula
•The hot gas is emitting light
Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/
Colder, darker nebulae
Dark dust blocking the hot
gas behind it
NOAO/AURA/NSF Image from
http://hubblesite.org/newscenter/archive/releases/nebula/dark/2001/12/image/c/results/50/
Protostars
Gravity pulls huge nebulas of hydrogen gas
and dust into a single spinning cloud.
As the particles crash into each
other, the matter heats up….about
15 million degrees.
Fusion begins…..
The mass begins to shine brightly.
A star is born!
Young
stars
form in
nebulae
from Small
Magellanic
Cloud
Image at
http://hubblesite.org/newscenter/archive/releases/2007/04/image/a/results/50/
Star-forming region in the Large Magellanic Cloud:
http://hubblesite.org/newscenter/archive/releases/2008/31/image/a/results/50/
Interstellar “eggs”
Movie at http://www.stsci.edu/EPA/PR/95/44/M16.mpg
Medium-Sized Stars
Hydrogen fuel is fused into helium at the star’s
core until the hydrogen is used up.
The core shrinks, heats up, & releases energy.
The energy causes the star’s outer layers to
expand, cool and become redder.
The core heats up and releases energy.
The star heats, expands, reddens and
becomes a ……
In a few Billion years… Red
Giant
Image at http://hubblesite.org/newscenter/archive/releases/1997/26/image/a/
Red Giant
The helium core continues to heat.
At ~ 200 million degrees the helium
atoms fuse to form carbon atoms and the
last of the hydrogen gases drift away.
These drifting gases form a nebula ring around
the star.
The star is dying. It grows fainter and
fainter.
Gravity causes its matter to collapse
inward.
The star is squeezed into a……
White Dwarf
They are superdense stars with carbon cores.
Since all of the mass of a star the size of
our sun has been squeezed into the size
of the earth,
all of the atoms are crowded together.
By 5 billion years… White Dwarf
Small, but very hot
Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/1998/39/results/50/
They are so packed together…..
A chunk of the white dwarf the size of a sugar cube
Would equal the mass of a CAR!
When the white dwarf’s energy is
gone,
it becomes a dead star known as a
black dwarf.
This is a white dwarf with a nebula cloud around it.
How long will a star live?
Our sun, a medium sized star, will live
about 10 billion years.
Small stars will live about 100 billion years.
Large stars will only live a few billion years..
Objectives for today!
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Describe how color indicates the temperature of a
star
Explain how a scientist can identify a star’s
composition
Describe how scientists classify stars.
Describe different types of stars.
Describe the quantities that are plotted in the H-R
diagram.
Explain how stars at different stages in their life cycle
appear on the H-R diagram.
Massive
Stars are
different
On the “Main
Sequence” but
not for long
Image from
http://hubblesite.org/newscenter/archive/releases/nebula/emission/1997/33/results/50/
Massive Stars
……begin with about 6 times as much mass as our sun.
Like medium sized stars:
They burn hydrogen at first.
They redden as their helium core forms.
But, instead of becoming red giants ….
they become supergiants.
Betelgeuse—Red Supergiant
Image from http://hubblesite.org/newscenter/archive/releases/star/massive%20star/1996/04/image/a/results/50/
As their cores heat up,
they fuse from helium….
to carbon…..
to oxygen and nitrogen….
to iron.
Then the fusion stops.
What happens next?
When the fuel runs out, gravity collapses the core
even more.
The iron core absorbs energy instead of releasing it….
The star breaks apart in a terrific
A Nova!
The entire sky is lit up for weeks.
The temperature can be more than 100 billion degrees.
The iron atoms fuse into uranium.
The uranium and gases explode into space.
A gigantic cloud of gas and dust is left and
may become a new nebula.
If it is super big it is called a
Supernova!
New stars, like our earth, form from these remains.
This supernova is
surrounded by a nebula ring.
Neutron Stars
After the supernova explosion of a star 6-30 times
the mass of the sun, a neutron star remains.
How big is it?
It’s only about 16Km in diameter,
but it has so much mass packed into it,
a chunk the size of a sugar cube
has the mass of ~ 100
MILLION CARS!!!
Stars 30 or more times the mass of our sun live
even shorter lives and face a strange fate……
After the supernova explosion,
the star’s core is so massive,
it is swallowed up by its own gravity.
The core’s gravity is so strong that even light can’t
escape.
The core has become a…..
Black Hole
The gravity from this black hole
is pulling this matter into itself.
Black
Hole
Image at http://hubblesite.org/newscenter/archive/releases/2002/30/image/a/results/50/
Black holes are like invisible cosmic vacuum cleaners.
They swallow both matter and energy.
How can we find them if we can’t see them?
We can’t, for sure.
Matter falling into a black hole
releases large bursts of X-rays.
We can detect these.
Now, let’s do a quick review.
Objectives for today!
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Describe how color indicates the temperature of a
star
Explain how a scientist can identify a star’s
composition
Describe how scientists classify stars.
Describe different types of stars.
Describe the quantities that are plotted in the H-R
diagram.
Explain how stars at different stages in their life cycle
appear on the H-R diagram.