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Chap. 30
The Sun 30.1
Measuring Stars 30.2
Stellar Evolution 30.3
The Sun 30.1
Objectives
• explore the
structure of the Sun
• describe the solar
activity cycle and
how the Sun affects
the Earth
• compare the
different types of
spectra
I. How do we learn about it?
I. How do we learn about it?
A. Using solar observatories
Dunn Solar Telescope
Sacramento Peak, NM
http://hesperia.gsfc.nasa.gov
I. How do we learn about it?
A. Using solar observatories
B. Using satellites
Solar Heliospheric
Observatory
(SOHO)
http://sohowww.nascom.nasa.gov/
II. Properties
II. Properties
A. The Sun has a very large radius
Radius
Sun: 695,000 km
Earth: 6,400 km
II. Properties
A. The Sun has a very large radius
B. The Sun is very massive
Mass
Sun: 2.0 x 1030 kg
Earth: 6.0 x 1024 kg
II. Properties
A. The Sun has a very large radius
B. The Sun is very massive
C. The density is similar to that of
the gas giant planets.
II. Properties
A. The Sun has a very large radius
B. The Sun is very massive
C. The density is similar to that of
the gas giant planets.
1. Outer portion is not very dense
II. Properties
A. The Sun has a very large radius
B. The Sun is very massive
C. The density is similar to that of
the gas giant planets.
1. Outer portion is not very dense
2. Inner portion is much denser
II. Properties
A. The Sun has a very large radius
B. The Sun is very massive
C. The density is similar to that of
the gas giant planets.
D. Physical state of matter:
.
II. Properties
A. The Sun has a very large radius
B. The Sun is very massive
C. The density is similar to that of
the gas giant planets.
D. Physical state of matter: plasma.
III. Layers of Atmosphere
III. Layers of Atmosphere
A. Photosphere
III. Layers of Atmosphere
A. Photosphere
1. Lowest layer
2. Only about 400 km thick
3. Average temp: 5800 K
4. Emits light we can see
III. Layers of Atmosphere
A. Photosphere
B. Chromosphere
III. Layers of Atmosphere
A. Photosphere
B. Chromosphere
1. Thicker layer (about 2500 km)
2. Hotter (average temp: 30,000 K)
3. Difficult to see, except during
eclipse
III. Layers of Atmosphere
A. Photosphere
B. Chromosphere
C. Corona
III. Layers of Atmosphere
A. Photosphere
B. Chromosphere
C. Corona
1. Outermost layer
2. Extends several million km
3. Very hot (1 to 2 million K)
IV. Solar Activity
Caused when sun’s magnetic field interrupts its
atmosphere
IV. Solar Activity
A. Solar Wind
IV. Solar Activity
A. Solar Wind
1. Charged particles from sun
traveling at high speeds (400 km/s)
IV. Solar Activity
A. Solar Wind
1. Charged particles from sun
traveling at high speeds (400 km/s)
2. Deflected by our magnetic field
IV. Solar Activity
A. Solar Wind
1. Charged particles from sun
traveling at high speeds (400 km/s)
2. Deflected by our magnetic field
3. Causes auroras
http://www.castlegate.net/
IV. Solar Activity
A. Solar Wind
B. Sun Spots
http://www.galacticimages.com/
IV. Solar Activity
A. Solar Wind
B. Sun Spots
1. Appear on photosphere
IV. Solar Activity
A. Solar Wind
B. Sun Spots
1. Appear on photosphere
2. Look dark because they are cooler
IV. Solar Activity
A. Solar Wind
B. Sun Spots
1. Appear on photosphere
2. Look dark because they are cooler
3. Associated with solar wind
IV. Solar Activity
A. Solar Wind
B. Sun Spots
C. Solar Flares
IV. Solar Activity
A. Solar Wind
B. Sun Spots
C. Solar Flares
1. Violent eruptions from surface
IV. Solar Activity
A. Solar Wind
B. Sun Spots
C. Solar Flares
1. Violent eruptions from surface
2. Occur in corona
IV. Solar Activity
A. Solar Wind
B. Sun Spots
C. Solar Flares
1. Violent eruptions from surface
2. Occur in corona
3. Some the size of Earth
IV. Solar Activity
D. Solar Prominence
IV. Solar Activity
D. Solar Prominence
1. Less violent than flares
IV. Solar Activity
D. Solar Prominence
1. Less violent than flares
2. Cool sheets of gas that condense
from corona
IV. Solar Activity
D. Solar Prominence
1. Less violent than flares
2. Cool sheets of gas that condense
from corona
3. Some rain back material on surface
V. Interior of Sun
V. Interior of Sun
A. Core
V. Interior of Sun
A. Core
1. Site of fusion (energy production)
2. Density of 160 g/cm3 (15 x denser
than lead)
3. Temperature of about 15 million K
4. Extends 25% to outside
V. Interior of Sun
A. Core
B. Radiative Zone
V. Interior of Sun
A. Core
B. Radiative Zone
1. Extends another 60% to outside
2. Temp. is about 2 million K
3. Passes energy (photons) from atom
to atom
V. Interior of Sun
A. Core
B. Radiative Zone
C. Convective Zone
V. Interior of Sun
A. Core
B. Radiative Zone
C. Convective Zone
1. Final 15%
2. Energy is carried via moving gas
volumes
3. Temp. is about 5700 K
VI. Fusion
VI. Fusion
A. Joining of nuclei
VI. Fusion
A. Joining of nuclei
B. Occurs at very high temp./pressure
VI. Fusion
A. Joining of nuclei
B. Occurs at very high temp./pressure
C. Opposite of fission
VI. Fusion
A. Joining of nuclei
B. Occurs at very high temp./pressure
C. Opposite of fission
D. Mass is lost during process
E=
2
mc
VI. Fusion
A. Joining of nuclei
B. Occurs at very high temp./pressure
C. Opposite of fission
D. Mass is lost during process
E. Tremendous amount of energy
produced
1354
2
J/m
VII. Three types of Spectra
VII. Three types of Spectra
A. Continuous spectra
Shows all the colors with no breaks
VII. Three types of Spectra
A. Continuous spectra
B. Emission spectra
Only certain lines produced (depending on
elements present
VII. Three types of Spectra
A. Continuous spectra
B. Emission spectra
C. Absorption spectra
Light passes through a gas and some of it is
absorbed (leaving dark, ‘missing’ sections)
VIII. Composition of Sun
VIII. Composition of Sun
A. Hydrogen (70%)
VIII. Composition of Sun
A. Hydrogen (70%)
B. Helium (28%)
VIII. Composition of Sun
A. Hydrogen (70%)
B. Helium (28%)
C. Trace elements
(O, C, Ne, Fe, N, Si, Mg, S)
The End
Measuring the Stars – 30.2
Objectives
• describe star
distribution and
distance
• classify the types of
stars
• summarize the
interrelated
properties of stars
I. Groups of stars
Pleiades
I. Groups of stars
A. Constellations
Groups of stars named after animals/mythological creatures
I. Groups of stars
A. Constellations
Orion
I. Groups of stars
A. Constellations
Betelgeuse
Rigel
Orion
I. Groups of stars
A. Constellations
B. Star Clusters
A group of stars that are bound by gravity
I. Groups of stars
A. Constellations
B. Star Clusters
1. Open cluster
Pleiades
Stars are loosely bound by gravity
I. Groups of stars
A. Constellations
B. Star Clusters
1. Open cluster
2. Globular cluster
M13, in Hercules
Tightly bound stars, relatively close together
I. Groups of stars
A. Constellations
B. Star Clusters
C. Binaries
Algol – a blue dwarf
Two stars that are gravitationally bound.
II. Stellar Positions and Distances
II. Stellar Positions and Distances
A. Stellar distance
II. Stellar Positions and Distances
A. Stellar distance
1. Light year (ly)
The distance traveled by light in one year.
Calculate this!
Light travels at a speed of
300,000 km/s. How many
miles is a light year?
Calculate this!
Proxima Centauri is 4.24 light
years. How many kilometers
is this star?
II. Stellar Positions and Distances
A. Stellar distance
1. Light year (ly)
2. Parsec (pc)
The distance of a star when it appears to shift
one second of a degree due to parallax.
1 pc = 3.26 ly.
II. Stellar Positions and Distances
A. Stellar distance
1. Light year (ly)
2. Parsec (pc)
3. Parallax
The apparent shift in position of an object as
the observer’s location changes
Calculate this!
The brightest star in
the sky (besides the
Sun) is Sirius. It is
2.6 pc from Earth.
How long does it
take light from Sirius
to reach us?
II. Stellar Positions and Distances
B. Other Properties of Stars
http://astronote.org
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
How bright a star appears. (affected by
luminosity and distance)
Magnitude
The lower the number the brighter
the object.
Each value increase equates to
about 2.512 decrease in brightness.
Magnitude of celestial objects
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
2. Absolute Magnitude
How bright a star would appear at 10 pc. (This
can be calculated if you know the actual distance.)
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
2. Absolute Magnitude
3. Luminosity
The energy output from the surface of a star.
Can be measured in joules/second or watts.
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
2. Absolute Magnitude
3. Luminosity
4. Spectra of Stars
The types (colors) of light given off
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
2. Absolute Magnitude
3. Luminosity
4. Spectra of Stars
a. Determined by temperature
Cooler stars have more lines in spectra
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
2. Absolute Magnitude
3. Luminosity
4. Spectra of Stars
a. Determined by temperature
b. Given a letter & number ranking
O5, A4, A5, G2 (sun), etc.
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
2. Absolute Magnitude
3. Luminosity
4. Spectra of Stars
a. Determined by temperature
b. Given a letter & number ranking
c. Light spectra can shift due to
motion
II. Stellar Positions and Distances
B. Other Properties of Stars
1. Apparent Magnitude
2. Absolute Magnitude
3. Luminosity
4. Spectra of Stars
5. H-R diagram (Hertzsprung-Russell)
Used to classify stars based on spectra & magnitude
The End
Stellar Evolution – 30.3
Objectives
• Explain how
astronomers learn
about the internal
structure of stars
• Describe how the
Sun will change
during its lifetime
and how it will end
• Compare the
evolutions of stars of
different masses
I. Introduction
I. Introduction
A. A star is balances two forces
I. Introduction
A. A star is balances two forces
1. Inward force:
.
I. Introduction
A. A star is balances two forces
1. Inward force: gravity
2. Outward force: _________________
I. Introduction
A. A star is balances two forces
1. Inward force: gravity
2. Outward force: fusion and radiation
I. Introduction
B. Structure of a star depends on:
I. Introduction
B. Structure of a star depends on:
1. Composition
Elements a star is made of
I. Introduction
B. Structure of a star depends on:
1. Composition
2. Mass
The total amount of material in a star
I. Introduction
B. Structure of a star depends on:
1. Composition
2. Mass
Gravity
Pull inward which is balanced by force outward
I. Introduction
B. Structure of a star depends on:
1. Composition
2. Mass
Gravity
Temperature
Higher temperature counter higher gravity.
I. Introduction
B. Structure of a star depends on:
1. Composition
2. Mass
Gravity
Temperature
Rate of Fusion
When temperatures increase so do reaction rates.
I. Introduction
B. Structure of a star depends on:
1. Composition
2. Mass
Luminosity
Gravity
Temperature
Rate of Fusion
Star produces more energy, and is brighter.
II. Fusion
Energy producing reaction in stars
II. Fusion
A. Main sequence
stars
Most stars fall in this category
II. Fusion
A. Main sequence stars
1. Start by fusing H + H to He
II. Fusion
A. Main sequence stars
1. Start by fusing H + H to He
2. He + He + He to C
II. Fusion
A. Main sequence stars
1. Start by fusing H + H to He
2. He + He + He to C
3. He + C to oxygen
II. Fusion
A. Main sequence stars
1. Start by fusing H + H to He
2. He + He + He to C
3. He + C to oxygen
4. He + O to neon
II. Fusion
A. Main sequence stars
1. Start by fusing H + H to He
2. He + He + He to C
3. He + C to oxygen
4. He + O to neon
5. He + Ne to magnesium
II. Fusion
A. Main sequence stars
1. Start by fusing H + H to He
2. He + He + He to C
3. He + C to oxygen
4. He + O to neon
5. He + Ne to magnesium
6. This stops at iron because fusion of
larger elements is no longer
favorable.
III. Life cycle of Sun
III. Life cycle of Sun
A. Star formation
III. Life cycle of Sun
A. Star formation
1. Nebula collapses on itself from its
own gravity
Orion Nebula
Nebula is an interstellar cloud of gas and dust
III. Life cycle of Sun
A. Star formation
1. Nebula collapses on itself from its
own gravity
2. Protostar forms in center of disk
shape, emitting lots of infrared light
III. Life cycle of Sun
B. Fusion begins. . .
III. Life cycle of Sun
B. Fusion begins. . .
1. when minimum temperature is
reached
III. Life cycle of Sun
B. Fusion begins. . .
1. when minimum temperature is
reached
2. this often illuminates surrounding
gases
Rosette Nebula
III. Life cycle of Sun
B. Fusion begins. . .
1. when minimum temperature is
reached
2. this often illuminates surrounding
gases
3. star enters main-sequence phase –
primarily converting H to He.
True or False?
Large main-sequence stars last
longer than smaller main-sequence
stars.
True or False?
Large main-sequence stars last
longer than smaller main-sequence
stars.
False – larger stars get hotter, and use
their fuel up faster.
III. Life cycle of Sun
C. Becoming a Red Giant
Betelgeuse
A larger, cooler star that is very luminous.
III. Life cycle of Sun
C. Becoming a Red Giant
1. After about 10 billion years, hydrogen
is used up
III. Life cycle of Sun
C. Becoming a Red Giant
1. After about 10 billion years, hydrogen
is used up
2. Core of star is made of He
III. Life cycle of Sun
C. Becoming a Red Giant
1. After about 10 billion years, hydrogen
is used up
2. Core of star is made of He
3. Layer of gas surrounding core does
fusion, causing gases to expand and
cool
III. Life cycle of Sun
C. Becoming a Red Giant
1. After about 10 billion years, hydrogen
is used up
2. Core of star is made of He
3. Layer of gas surrounding core does
fusion, causing gases to expand and
cool
4. Outer layers are driven away due to
decrease in surface gravity
III. Life cycle of Sun
C. Becoming a Red Giant
1. After about 10 billion years, hydrogen
is used up
2. Core of star is made of He
3. Layer of gas surrounding core does
fusion, causing gases to expand and
cool
4. Outer layers are driven away due to
decrease in surface gravity
5. He in core reacts to form C
III. Life cycle of Sun
D. Becoming a White Dwarf
III. Life cycle of Sun
D. Becoming a White Dwarf
1. Star is not big enough to further react
carbon
III. Life cycle of Sun
D. Becoming a White Dwarf
1. Star is not big enough to further react
carbon
2. Gases surrounding star expend and
are driven off
III. Life cycle of Sun
D. Becoming a White Dwarf
1. Star is not big enough to further react
carbon
2. Gases surrounding star expend and
are driven off
3. Core remains as small, hot, earthsized object
III. Life cycle of Sun
D. Becoming a White Dwarf
1. Star is not big enough to further react
carbon
2. Gases surrounding star expend and
are driven off
3. Core remains as small, hot, earthsized object
4. This star is made of carbon
IV. Massive Stars
Monocerotis
IV. Massive Stars
A. Same beginning – but hydrogen
fusion happens quickly
IV. Massive Stars
A. Same beginning – but hydrogen
fusion happens quickly
B. Star expands and contracts to
repeatedly, forming variety of
elements (not bigger than Fe)
IV. Massive Stars
A. Same beginning – but hydrogen
fusion happens quickly
B. Star expands and contracts to
repeatedly, forming variety of
elements (not bigger than Fe)
C. Mass if lost by stellar wind
IV. Massive Stars
D. Size determines fate
IV. Massive Stars
D. Size determines fate
1. If star’s mass is < 1.4 x Sun’s size it
becomes a white dwarf.
IV. Massive Stars
D. Size determines fate
1. If star’s mass is < 1.4 x Sun’s size it
becomes a white dwarf.
2. If star’s mass is > 1.4 x Sun’s size it’s
gravity pulls gases inward, merging
protons and electrons in
.
IV. Massive Stars
D. Size determines fate
1. If star’s mass is < 1.4 x Sun’s size it
becomes a white dwarf.
2. If star’s mass is > 1.4 x Sun’s size it’s
gravity pulls gases inward, merging
protons and electrons in neutrons.
IV. Massive Stars
D. Size determines fate
1. If star’s mass is < 1.4 x Sun’s size it
becomes a white dwarf.
2. If star’s mass is > 1.4 x Sun’s size it’s
gravity pulls gases inward, merging
protons and electrons in neutrons.
a. These are neutron stars
IV. Massive Stars
D. Size determines fate
1. If star’s mass is < 1.4 x Sun’s size it
becomes a white dwarf.
2. If star’s mass is > 1.4 x Sun’s size it’s
gravity pulls gases inward, merging
protons and electrons in neutrons.
a. These are neutron stars
b. They are very dense – 3x Sun’s
mass squeezed into 10 km radius.
IV. Massive Stars
D. Size determines fate
1. If star’s mass is < 1.4 x Sun’s size it
becomes a white dwarf.
2. If star’s mass is > 1.4 x Sun’s size it’s
gravity pulls gases inward, merging
protons and electrons in neutrons.
a. These are neutron stars
b. They are very dense – 3x Sun’s
mass squeezed into 10 km radius.
c. Particles from outer layer bounce
off neutron star creating supernova
IV. Massive Stars
D. Size determines fate
1. If star’s mass is < 1.4 x Sun’s size it
becomes a white dwarf.
2. If star’s mass is > 1.4 x Sun’s size it’s
gravity pulls gases inward, merging
protons and electrons in neutrons.
3. If star’s mass is 3 x Sun’s size it
becomes a black hole.
The End