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Characteristics of Stars
and
The Life of Stars
Chapter 21
2012
How are stars formed and what are they
made of?
• There are huge clouds of Hydrogen gas in outer
space. (Nebula)
• Over time gravity causes gas to come together.
• Once enough gas comes together, there is enough
pressure to cause a nuclear reaction “lighting” the
star. (a star is born)
• Nuclear fusion is what causes a star to “burn”
• Hydrogen is converted into helium during nuclear
fusion.
1. Imaginary patterns made up of stars are called constellations.
2. What gases are stars made of? Hydrogen and Helium
3. How do stars produce energy? Nuclear fusion
Classifying Stars
1. What are some characteristics scientists use to
classify stars? By their color, temperature, size,
composition, and brightness
2. What can a star’s color tell us? It can tell us the
stars temperature. Cooler stars appear red and hotter
stars are blue
3. The largest stars are called red giants or super
giants.
4. The smallest stars are called neutron stars.
5. What is a spectrograph?
A spectrograph breaks light into colors and
produces an image of the resulting spectrum.
Dark lines in the image can ID the chemicals
present.
How is it used?
A spectrograph can tell scientists what distant
objects are composed of.
Check out this cool spectroscopy
video
The spectrum and spectrographs
Brightness of stars
6. What does the brightness of a star depend on?
Size and temperature
7. What is apparent brightness? A stars brightness
as seen from Earth. Affected by distance
8. What is absolute brightness? The brightness a
star would have if it were a standard distance from
the Earth.
9. Why is finding a stars brightness so difficult?
An astronomer must find the apparent brightness
and the distance from the Earth.
10. What is a light year? The distance that light can
travel in one year. (9.5 million million kilometers)
Milkyway galaxy 100,000
light years across.
The Andromeda galaxy is 2.5
million light years away from
Earth
The speed of light
• The speed of light is 186,000 miles per
second or 670,616,629 mph
• That means you can travel around the Earth
7.5 times in one second
11. What the heck is a parallax? The apparent
change in position of an object when you look at it
from different places
Hertzsprung- Russell Diagram
12. What is the Hertzsprung- Russell diagram? The
diagram plots the temperature and absolute brightness
the star would have.
Size comparison of stars
Star Size Comparison Video
Another Cool Video
Life of Stars
1.Nebula- a large cloud of gas and dust spread out in an immense
volume.
2. A star on the other hand is made of a large amount of gas in a
small volume.
3. How does a star form from a cloud of gas? Gravity pulls gas
and dust into a dense ball eventually triggering nuclear fusion.
4. The life of a star depends on its mass.
-Stars with less mass than the sun burn their fuel slowly
and can live up to 200 billion years.
Medium sized stars can live up to 10 billion years.
The Death of Stars
5. What happens to a star the begins to run out of fuel? The core
shrinks, and the outer portion expands.
6. What happens when it completely runs out of fuel? The star
becomes a white dwarf, a neutron star or a black hole.
White Dwarfs
7. Planetary Nebula- The outer parts of a dying star drifting into outer
space forming a glowing cloud of gas
8. White dwarf- the core of a dying star the size of Earth with as
much mass as the sun. (1 spoonful has as much mass as a large
truck.
Supernova
9. When a high mass star begins to die it turns into a supergiant.
10. When a supergiant runs out of fuel it can suddenly explode. This
explosion is called a super nova.
White dwarf compared to Earth
Neutron Star
11. Describe a neutron star: neutron stars are the remains of high
mass stars. Smaller and denser than white dwarfs. They can
contain as much as three times the mass of the sun but only 25 km
in diameter!
12. A spinning neutron star is called a pulsar.
Black Holes
13. What is a black hole? A black hole is an object with
gravity so strong nothing, not even light can escape it.
14. How can astronomers detect black holes if they cannot see
them? They use indirect evidence like gas near a black hole
that spins faster and faster. They can also detect heat and Xrays coming from it.
Life and Death of a Star
Wow!
A single sugar cube sized amount of white dwarf would weigh about 1
ton.
A white dwarf was once the size of the sun, but has been squeezed
down to the size of the Earth.
A white dwarf has burned off all its fuel and only carbon remains.
Wow continued
Neutron stars
A neutron star is about 20 km in diameter and has the mass of
about 1.4 times that of our Sun.
This means that a neutron star is so dense that on Earth, one
teaspoonful would weigh a billion tons!
How does gravity in space keep
objects in orbit?
We are made of stars!
• Once helium runs out, the nuclei of carbon, oxygen, and
other elements begin to fuse together.
• Since the heaviest element created in a star by nuclear
fusion reaction is iron, a large iron core eventually forms at
the center.
• At this point, gravity becomes overwhelming, the core
collapses, and an explosion occurs (supernova), during
which outer layers of gas and heavy elements are ejected to
space.
• These elements are recycled and form planets and
eventually the things on the planets like life forms!