Download Chapter10- Our Star - SFA Physics and Astronomy

Chapter 10
Our Star
Hydrostatic Equilibrium or
Gravitational Equilibrium
 The
outward pressure force
balances the inward gravitational
force everywhere inside the Sun.
Gravitational Equilibrium in the Sun.
The Sun’s Properties
The Sun's Atmosphere

Photosphere - "sphere of light", the
visible surface of the Sun

Chromosphere - "sphere of color",
visible during solar eclipses

Corona - the Sun's outermost
atmosphere. The outflow of gas in
this region is called the solar wind,
which is protons and electrons that
have escaped the Sun's gravity.
Transition
Zones
Solar Spectrum
The Chromosphere
Solar Corona
Auroras are caused by the solar wind.
 Solar wind is an outward flow of fastmoving charged particles
(mostly protons & electrons)

The Basic Structure of the Sun
The Sun's Interior

Thermonuclear core - the central region of
Sun where fusion takes place due to high
temperatures and pressures.

Radiation zone - a region inside a star where
energy is transported outward by the
movement of photons (radiation).

Convection zone - a layer inside a star
where energy is transported outward by
means of heat flow through the gasses of
the star (convection).
Solar Density
and
Temperature
What makes the Sun shine?

Thermonuclear fusion at the Sun's core is
the source of the Sun's energy.
4 Hydrogen
Atoms
--------->
(fusion)
1 Helium + Light
Atom
Mass loss?
4  1 hydrogen = 6.693  10-27 kg
- 1 helium = 6.645  10-27 kg
---------------------------------------------Mass loss = 0.048  10-27 kg
The missing mass is converted to
pure energy ( i.e. light ) By Einstein’s
energy/mass equation.
E = mc2
What does this mean?
Mass can be transformed into light.
This occurs during fusion.
 Light be transformed into matter.
This occurs in pair production.


These are results from Einstein’s
theory of Special Relativity.
For one hydrogen-to-helium fusion event,
E = 4.3 x 10-12 Joules
This is a tiny number by itself ,
but when multiplied by the vast number of
hydrogen atoms undergoing fusion
and considering the rate of fusion in the Sun,
the total power released is equivalent to exploding
100 billion- 1 megaton H-bombs per second!
Our sunshine has a violent birth.
Helioseismology- Understanding the Sun’s
Interior
Modes of vibration

Vibrations on the
surface of the
Sun can be
detected by
Doppler shifts
Falling Gas
(Red)
Rising Gas
(Blue)
The Neutrino Problem
Standard solar model is the generally
accepted theory of solar energy
production.
Web

The model predicts that billions of
neutrinos per second flow from the Sun.

Neutrinos react very little with ordinary
matter so detecting them is difficult.

Neutrino telescopes indicate that only 1/3
of the neutrinos predicted by theory are
“seen.”
Solar Neutrino “Telescopes”
Solar Neutrino detector in
South Dakota. Cl nuclei
would turn into Ar nuclei
when they captured solar
neutrinos
Super –Kamiokande
experiment in Japan is one
of the world’s latest
neutrino detectors.
Convection Transports Energy Outward
Convection
Cell
Granulation- Convection Cells
in Photosphere
Sunspot Groups
Magnetic Field Lines
Lines closer together
Compass needles align
represent stronger magnetic
with the magnetic field lines
fields
Charged particles
spiral along field
lines
Sunspot
Pairs

Solar Prominence - a flame-like
protrusion seen near the limb of the Sun
and extending into the solar corona.
These follow magnetic field lines.

Solar Flare – Huge and sudden release
of energy on the solar surface, probably
caused when energy stored in magnetic
fields is suddenly released.
Solar Prominences – SOHO mission
Solar Flare –TRACE Mission
Sun in X-Ray
Corona
Sunspot Cycle

The rotation rate varies from once
every 25 days to once every 30 days.

This differential rotation twists the
magnetic field lines.

This causes the number of sunspots
to vary over an 11 year period.
Solar Cycle

A 22 - year period that is needed for
both the average number of spots
and the Sun’s magnetic field polarity
to repeat themselves. The Sun’s
polarity reverses on each new 11year sunspot cycle.
Magnetic Field lines become distorted due to the Sun’s
Differential Rotation
Simmary of Surface Features

Granules - convection features about 1000
kilometers in diameter seen constantly in
the solar photosphere.

Sunspot - a temporary cool region in the
solar photosphere created by protruding
magnetic fields.

Prominence - a flamelike protrusion seen
near the limb of the Sun and extending into
the solar corona.
Solar Telescope
End of Section