Chapter 14: Our Star • Once we learned the Sun’s energy
Examination of our Sun, the nearest output, scientists were at a loss to
explain it until Einstein showed that
star mass itself contains a tremendous
amount of energy
• The Sun shines with energy generated
by fusion of hydrogen into helium in the
Sun’s core Why does the Sun shine?
• The Sun shines because gravitational
• After a journey through the solar interior equilibrium keeps its core not and
lasting several hundred thousand dense enough to release energy
years, and then a 8min journey through through nuclear fusion
space, a small fraction of this energy Gravitational equilibrium is the natural
reaches Earth and supplies sunlight •
and heat balance between two competing forces
Gravitational equilibrium, the balance of the core, which is gravity pulling
• inward and pressure pushing outwards
between pressure and gravity, • The core originally became hot through
determines the Sun’s interior structure the release of energy by gravitational
and helps create a natural thermostat contraction, as gravity made the Sun’s
that keeps the fusion rate steady in the birth cloud contract
Sun
• If the Sun were not so steady, life on • The Sun was born with enough
hydrogen to steadily maintain its
Earth might not be possible gravitational equilibrium for about 10
• The Sun’s atmosphere displaces its billion years
own version of weather and climate,
governed by solar magnetic fields What is the Sun’s structure?
• Some solar weather, such as coronal
mass ejections, clearly affects Earth’s • The Sun’s interior layers, from the inside
magnetosphere out, are the core, the radiation zone,
and the convection zone
• Other claimed connections between • Atop the convection zone lies the
solar activity and Earth’s climate but photosphere, the layer from which
that may or may not be real photons can freely escape into space
• The Sun is important not only because Above the photosphere, which is the
it is our source of light and heat, but •
also because it is the only star near surface, are the chromosphere and the
enough for us to study in great detail corona
• The sun is a ball of plasma, a gas in
which many of the atoms are ionized
because of high temperature
14.1 • Even sunspots are bigger than our
planet
Why was the Sun’s energy source a
major mystery? • The Sun’s total output is called
luminosity
• Before we knew the difference between • Solar wind is the stream of charged
Earth and Sun no one realized how particles continually blown outward
much energy the Sun releases into from all directions of the Sun
space • The outmost layer of the Sun is the
corona, which emits Xrays • The next surface is the chromosphere •This is when photons bounce randomly
where the temperature drops and emits among gas particles
ultraviolet light •The migration of photons is called
• The lowest layer is the photosphere, radiative diffusion, when photons slowly
which is the visible surface of the sun make its way outward
• The convection zone is the outer layer •After energy emerges from the
More
Less
