The Sun

1
The Sun

• Our Star

2
Our Star

• Our star, the Sun, is a dazzling luminous ball
  of burning gas one hundred times the radius of
  the Earth. Viewed normally, the Sun seems
  peaceful and regular, but viewed through a
  telescope, the Sun is a teaming, explosive place
  where fountains of heated gas leap 100s of miles
  above the surface.

3
Scale of the Solar System

• The Sun dwarfs the rest of the solar system.
  100 times the radius of the Earth, the Sun has a
  mass 300, 000 times that of our planet.

4
Solar Facts

• The Sun is about 93 million miles from Earth.
• Surface gravity on the Sun is about 30 times that
  felt by a body on Earth.
• The Suns surface temperature is about 5,800 K.
• The Suns core temperature is about 15 million K.
• The Suns core is 100 times denser than water.

5
Solar Facts

• The mass of the Sun is about 333,000 times the
  mass of the Earth.
• It is estimated that the Sun releases about 4 X
  1026 watts into space from its surface.
• The Sun is composed of 71 hydrogen, 21 helium
  and 2 heavier materials such as carbon and iron.

6
The Suns Interior

• The Sun is composed of several layers
• The Photosphere
• The Chromosphere
• The Corona
• And two distinct zones
• Radiative Zone
• Convective Zone

7
The Photosphere

• The outside of the Sun is relatively
  transparent, however, with increased depth the
  Sun becomes opaque. The cause of this is that at
  a certain depth the weight of the overlying gas
  crushes the underlying gases together so tightly
  that they can not be seen.
• The photosphere
• makes up the portion of
• the Sun that we cannot see.

8
Radiative Zone

• Near the Suns core, energy is moved by
  radiation carried by photons (remember those?).
  This area is called the radiative zone. Because
  the gas there is so dense, before most photons
  travel an inch, they are absorbed by an atom and
  stopped. The photon will be re-emitted later
  only to be stopped by another atom.

9
Radiative Zone

• Like traffic stuck at a light, the photons are
  delayed. This delay is quite long, to the extent
  that the sunlight we see today was generated
  about 16 million years ago.

10
The Convection Zone

• Just below the photosphere where the gas is
  cooler and less transparent, the flow of energy
  is slowed. In this region, photons are even less
  effective at moving energy.

11
The Convective Zone

• Convection currents carry energy from this
  region toward the Suns surface. These are like
  similar currents within the Earth and the gas
  giant planets.
• This is why the
• region is called the
• convection zone.

12
The Convective Zone

• While we cant see these gases, we can infer
  their motion by observing tiny bright regions
  surrounded by darker areas that appear on the
  surface. These are called granules. These
  granulations form from bubbles of rising hot gas.

13
The Convective Zone

• These rising bubbles burst and cool, emanating
  heat and light into space. The cooling gases
  subside and turn dark, creating the dark edges
  that surround each granule.

14
The Convection Zone

• Using the Doppler Effect, scientists have
  measured how rapidly this granules rise and found
  that their average speed is about one kilometer
  per second (km/s).

15
The Suns Atmosphere

• Scientist refer to the very low density gases
  above the Suns photosphere as the Suns
  atmosphere. This atmosphere, like the Earths,
  becomes gradually thinner the farther it extends
  into outer space.

16
The Suns Atmosphere

• Youd think with the density of the gases
  decreasing, that the temperature would decrease
  too, but just the opposite occurs. Because they
  are more easily heated at higher altitudes, the
  gases burn with great intensity. The temperature
  immediately above the photosphere has an average
  temperature of several million Kelvin.

17
The Suns Atmosphere

• The Suns atmosphere consists of two major
  divisions the chromosphere lies directly about
  the photosphere and it is the Suns lower
  atmosphere.

18
Chromosphere

• The chromosphere consists of millions of jets of
  hot gas called spicules. Spicules are generally
  thousands of kilometers long. The chromospheres
  red color comes from the strong emission spectrum
  of hydrogen.

19
The Corona

• The outer-most layer of the Suns atmosphere is
  the corona. The temperature in the chromosphere
  is about 4,500 K, but only about 2,000 kms
  higher the temperature soars to 50,000 K.

20
The Corona

• Since rising into the corona from the
  chromosphere, the temperature of a gas may have
  climbed 1 million degrees. Despite its high
  temperatures, the corona has very little energy
  due to its lack of density.

21
Stellar Equilibrium

• Our Sun, like all healthy stars, exists in a
  state of equilibrium. Gravity pulls in the Suns
  mass toward its center with tremendous force.
  But, the Sun also pushes out (with heat and
  energy) with great force. It pushes out exactly
  as hard as gravity pulls it in.
• This balance of forces
• maintains the stability
• of our star. This is known
• as hydrostatic equilibrium.

22
Stellar Equilibrium

• Equilibrium comes at a price, however. In order
  to maintain its outward force, the Sun has to
  consume itself as fuel. As an area of limited
  resources, the Sun will one day exhaust its fuel
  supply and die. Every second the Sun consumes 4
  million tons of itself.

23
Pressure in the Sun

• The pressure that counter-balances gravitys
  forces comes from the rapid motion of atoms. For
  a better understanding of the Sun, we must
  understand pressure.
• Pressure cooker

24
Pressure in the Sun

• Pressure comes from atoms and molecules
  colliding. The more you compress something, the
  closer its atoms and molecules are and the more
  collisions that occur. This is called density.
  This creates pressure.

25
Pressure in the Sun

• The more you heat something, the faster its
  atoms and molecules move and the more violently
  they collide. This creates pressure as well.

26
The Ideal Gas Law

• Weve established the relationship between
  pressure and temperature and density. Stated
  formally, it is known as the Ideal Gas Law and it
  states
• Pressure Density X Temperature X some constant
• Scientists have calculated that given the mass
  of the Sun and its tremendous gravitational pull
  inward, its internal temperature must be about 15
  million K to remain at equilibrium.

27
Warm Up

• Define the following The Photosphere, The
  Chromosphere, The Corona, Radiative Zone
• and Convective Zone
• 2. What is the diameter and mass of the Sun
  relative to Earth?
• 3. What are granules and how do they form?
• 4. What are the two layers of the Suns
  atmosphere?
• 5. What is stellar equilibrium? Why is it
  important?
• According to the Ideal Gas law, what effects
  pressure?
• What is the cost to the Sun for maintaining its
  equilibrium?
• What is a spicule?

28
Powering the Sun

• Energy created by the Sun is eventually lost
  into outer space by heat and light. If the Sun
  did not replace this lost heat, the pressure
  pushing the Sun out would diminish until the Sun
  eventually collapsed under its own gravity.

29
Powering the Sun

• Many early astronomers believed that the Sun
  burned conventional fuels such as coal. The
  supply of coal would have been exhausted after
  about 10,000 years.

30
Powering the Sun

• In the late 1800s, Lord Kelvin (English) and
  Hermann Helmholtz (German) independently proposed
  that the Sun was not at hydrostatic equilibrium,
  but was actually slowly collapsing.
• The Sun could only
• sustain itself for
• about 10 million
• years doing this.

31
Powering the Sun

• In 1899, T.C. Chamberlin suggested that
  subatomic energy might power the stars, but could
  offer no explanation as to how.

32
Powering the Sun

• It was not until 1905 that Albert Einstein
  proposed that energy might actually come from
  mass with his equation Emc2.

33
Einsteins Equation

• E mc2, where E is energy (joules), m is mass
  and c is the speed of light (3X108 m/s2). The
  amount of energy that is available from nuclear
  reactions is staggering. One gram of mass (one
  paper clip) could be converted into 20 kilotons
  worth of
• energy.

34
Follow Up Work

• In 1919, Arthur S. Eddington showed that
  converting hydrogen to helium could provide
  enough energy to power stars including our Sun.

35
Follow Up Work

• Physicists Hans Bethe and Carl von Weizsacker
  proposed that the Sun produced its energy by the
  process of nuclear fusion.

36
Nuclear Fusion

• Under normal conditions, hydrogen nuclei repel
  each other due to similar electrical charges, but
  under conditions of extreme heat when these atoms
  collide their nuclei are driven extremely
• close to each other.

37
The Proton-Proton Chain

• Hydrogen fusion takes place in three stages
  called the proton-proton chain.

38
The Proton-Proton Chain

• Stage 1 Two hydrogen nuclei collide to form a
  hydrogen isotope called 2H. This process
  converts one proton into a neutron and releases a
  positron (e) and a
• neutrino (v).

39
The Proton-Proton Chain

• Step 2 The 2H nucleus collides with a 1H
  nucleus to make an isotope of 3He. This process
  releases energy in the form of gamma rays (g).

40
The Proton-Proton Chain

• Stage 3 Two 3He nuclei collide together and
  fuse. This forms two separate particle types,
  4He and two 1H nuclei.

41
Searching for Neutrinos

• During Stage 1 of the proton-proton chain, we
  saw that the Sun generates neutrinos in the
  fusion process. Scientists have searched for
  these neutrinos as evidence of the fusion process
  in the Sun.

42
Searching for Neutrinos

• Scientists calculated the amount of neutrinos
  that they expected to be generated by the Sun.
  Because neutrinos have so little mass, they can
  penetrate anything and are very hard to detect,
  like bullets shooting through tissue paper.

43
Searching for Neutrinos

• The first neutrinos detectors were built in the
  late 1970s, one in Japan and one in the United
  States. They were built deep under ground for
  shielding from
• cosmic rays.
• The detectors were
• filled with a solution
• like heavy water.

44
Searching for Neutrinos

• When a neutrino passes through the solution and
  collides with a neutron, it creates a flash of
  light from an electron. Light sensors count the
  flashes.

45
Searching for Neutrinos

• Another thing that makes neutrinos hard to
  detect in that they come in three separate
  structures (called a, b and g-neutrinos). They
  transform themselves as the travel. Initially,
  scientist only detected a third of the neutrinos
  that they expected to find. They could only
  detect one of the types.

46
Summary of Point

• Not until very recently have we discovered
  evidence of how our Sun actually manufactures its
  energy. We didnt even have a good guess until
  the 1950s. There is still a lot that we do not
  know about our star!

47
Solar Magnetic Activity

• The Suns magnetic field gives rises to several
  solar phenomenon. These include Solar
  prominences, Solar prominences, Sun spots and the
  Earths aurora borealis.

48
Solar Phenomenon

• Solar prominences Are magnetic disturbances in
  the Suns atmosphere. Gigantic plumes of hot gas
  from the lower chromosphere jump into the corona.
  Prominences form as cooling gas trapped within
  the Suns magnetic field. They are usually seen
  arcing between sunspots.

49
Solar Phenomenon

• Solar flares These are not well understand but
  are thought to be the Suns magnetic field being
  twisted by hot, rising gas. The fields can only
  be twisted to much, before they readjust, forming
  a flare. Like a rubber-band toy.

50
Solar Phenomenon

• Sun spots charged particles are attracted to
  the Suns magnetic field. These particles spiral
  down the magnetic field lines and slow the ascent
  of heat. This creates colder areas on the
  surface. These cool, black areas are known as
  sunspots.

51
The Solar Wind

• As the Sun burns, it releases heat and energy in
  several forms. One of these forms is as charged
  particles. These particles streak across space
  at the speed of light. They strike the Earths
  magnetic field and glow in an eerie phenomenon
  known as the aurora borealis.

52
Solar Phenomenon
53
Warm Up

• What is the source of the Suns energy?
• Describe the three stages of the proton-proton
  chain.
• What is a solar prominence? How does they occur?
• What is a solar flair? How do they occur?
• What is a sun spot? How do they occur?
• What is a neutrino? Why are scientists looking
  for they so hard?
• What is the aurora borealis?

54
Writing Assignment

• Step 1 Within your group, discuss current
  issues in science. Focus on this question, Is
  science destructive?
• Step 2 On a piece of paper, please write
• Paragraph 1 State three examples that you
  discussed and tell why they are relevant to the
  question.
• Paragraph 2 Explain your personal position
  concerning the question, Is science destructive?

55
Solar Cycles

• We have lots of solar cycles.