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The Stars
Chapter 14
Great Idea:
The Sun and other stars use nuclear fusion
reactions to convert mass into energy. Eventually,
when a star’s nuclear fuel is depleted, the star
must burn out.
The Nature of Stars
• Astronomy
– Oldest science
• Star
– Fusion reactor in space
– Ball of gas
• All stars have a beginning and an
ending
Measuring the Stars with
Telescopes and Satellites
• Electromagnetic radiation
• Measurement of photons
– Wavelength
– Intensity
– Direction
– Variation
The Structure of the Sun
• Structure
– Stellar core (hottest part, dense gas in a plasmic state)
– Convection zone (rising gas from the core that cools)
– Photosphere (the region from which externally received
light originates)
– Chromosphere (red color, thin layer, hotter and more
dense than the photosphere)
– Corona (external plasma atmosphere that extends
hundreds of thousands or millions of miles into space)
• Solar wind
– Stream of charged particles ejected from the upper
atmosphere
The Sun's Chromosphere
and Corona
Earth’s Magnetic Field
Northern Lights
The Sun’s Energy
Source: Fusion
• Sun’s energy source
• Hydrogen (1 proton) converted to helium
(2 protons)
• Life expectancy is 11 billion years, and the
sun is currently 4.5 billion years
The Astronomical
Distance Scale
• Time
– Light-years (about 8,000 miles per
second, or 6 trillion miles in 1 year)
– The closest star to our sun is Proxima
Centauri at 4.3 light years away (25.8
trillion miles)
• Measurement
– Triangulation
– Cepheid variable
The Hertzsprung-Russel
Diagram
• Star groupings
– Main-sequence stars
– Red giants
– White dwarfs
The Birth of Stars
• Nebular hypothesis
– Pierre Laplace (gaseous clouds called
nebulae rotate, cool, and gradually
collapse and flatten due to gravity to
form stars and planets)
The Eagle Nebula
Formation of a Planetary
System
The Main Sequence and
the Death of Stars
• Stars much less massive than the
Sun
– Brown dwarf
– Glows 100 billion years
• No change in size, temperature, energy
output
The Main Sequence and
the Death of Stars – cont.
• Stars about the mass of the sun
– Hydrogen burning at faster rate
• Move off main sequence
– Helium burning
– Red giant
– Begin collapse
– White dwarf
The Life Cycle of the Sun
Just how big are the stars?
The Main Sequence and
the Death of Stars – cont.
• Very large stars
– Successive collapses and burnings
– Iron core
– Catastrophic collapse
• Supernova
Star Explosion
Black Holes
• Black hole
– Result of collapse large star
– Nothing escapes from surface
– Cannot see them
• See impact on other stars
• Detect x-rays, gamma rays
Cosmology
Chapter 15
Great Idea:
The universe began billions of years ago in the big
bang and it has been expanding ever since.
Galaxies
Edwin Hubble and the
Discovery of Galaxies
• Hubble
– Largest telescope
– Used Cepheid variable stars to measure
distance to nebula
• Galaxies
– Hubble discovered universe is billions of
galaxies
• Cosmology
Kinds of Galaxies
• Spiral
• Elliptical
• Irregular and dwarf
• Active galaxies
– Quasars
A Map of the Milky Way
A Typical Spiral Galaxy
A Typical Elliptical Galaxy
How BIG is the Universe??
The Redshift and
Hubble’s Law
The Redshift and
Hubble’s Law
• Redshift
• Hubble’s Law
– The more distant a galaxy, the faster it
recedes
–V = H x d
Photographs of Galaxies
and Their Spectra
What is the redshift??
Illustration of Hubble
Expansion
The Big Bang
The Big Bang
• Big Bang
– The universe began at a specific time in
the past, and it has been expanding
ever since
The Large-Scale
Structure of the Universe
• The Local Group
– Milky Way, Andromeda Galaxy, and
others
• Groups, clusters, superclusters
• Voids
The Sequence of “Freezings”
10–43 Second: The Freezing
of All Forces
• Two fundamental forces
– Gravity
– Strong-electroweak force
• Limit of our knowledge of universe
Dark Energy
What is Dark Energy?