lecture 11 the sun ii interior and solar wind. announcements test 2 is one week from tonight....
TRANSCRIPT
Lecture 11THE SUN II
Interior and Solar Wind
Announcements
• Test 2 is one week from tonight.– Similar format to test 1– More info next time
• Don’t forget the eclipse at sunset on Saturday.– Best viewing will be between 6:40 and 7:10.– Moon will be in Earth’s outer shadow until 8:25– Turn in your description (including a sketch or
photo) Monday for Bonus.
Solar Structure
• THE SOLAR ATMOSPHERE– Solar Wind
– Corona
– Chromosphere
– Photosphere The “Surface” of the Sun
• THE SOLAR INTERIOR– The Convection Zone
– The Radiative Zone
– The Core
Daily Grade 11 – Question 1
Which outer layer of the Sun gets its name from its reddish color visible during a total solar eclipse?
A. PhotosphereB. ChromosphereC. CoronaD. Reddishsphere
The Solar Wind
• Earth and all the planets in the Solar System are immersed in the Sun's expanding outer atmosphere.
• This out flowing of solar material (10 million tons per year) is called the solar wind.
• Spacecraft measurements show that the solar wind is fast (400 km/s, about a million miles per hour), thin (a few particles per cubic centimeter), and hot (several hundred thousand degrees).
Coronal Holes
X-ray images of the sun reveal coronal holes.
These arise at the foot points of open field lines and are the origin of the solar wind.
The Solar Sea
• The solar wind is an example of a plasma, meaning its atoms are divided into electrically charged particles - electrons, protons, and other ions.
• This allows it to carry with it magnetic fields from the corona which interact with the Earth's magnetic field.
• Most of the solar wind particles are deflected by the Earth's magnetic field, but some of these charged particles leak into the terrestrial environment.
The Sun-earth Connection
The Sun interacts with the Earth directly with its:
• electromagnetic radiation
• charged particles (solar wind)
• magnetic field
Genesis Spacecraft
• While the spacecraft was in orbit, it collected particles of the solar wind in specially designed high purity wafers.
• After two years, the sample collectors were re-stowed and returned to Earth.
• Although the parachute did not deploy, some collectors survived.
• The samples will be stored and cataloged under ultra-pure clean room conditions and made available to the world scientific community for study.
Genesis Spacecraft
Daily Grade 11 – Question 2
Genesis was a sample return mission. What did it return samples of?
A. A Comet
B. The Sun
C. Galactic Cosmic Rays
D. Mars
The Solar Interior
• Astronomers assume that the Sun is neither expanding nor contracting (hydrostatic equilibrium), not heating up or cooling down (thermal equilibrium), and is spherically shaped.
• Given these assumptions and knowledge of the Sun's chemical composition and surface temperature and pressure, it is possible to use high-speed computers to calculate a model for the solar interior, giving changing pressure and temperature conditions.
The Origin Of Solar Energy
• COMBUSTION. Given the mass of the Sun and the rate at which it is producing energy, if it were composed of coal or wood it would burn out in about 3,000 years.
• GRAVITATIONAL COLLAPSE. Given the size and mass of the Sun, if it were slowly collapsing, it would remain hot for about 20 million years. But geologists estimate the age of the Solar System to be about 4.5 billions years.
• NUCLEAR FUSION. Given the Sun's abundance of hydrogen and intense core temperature and pressure, conditions are favorable for the fusion of hydrogen into helium. The Sun could continue its present energy production for about 5 billion years using this fusion process. In this process mass is converted into energy according to Einstein's famous equation:
E = mc2
Nuclear Fusion Energy
Energy generation in the sun (and all other stars):
Nuclear Fusion
= fusing together 2 or more lighter nuclei to produce heavier ones.
Nuclear fusion can produce energy up to the production of iron;
For elements heavier than iron, energy is gained by nuclear fission.
Binding energy due to strong force = on short range, strongest of the 4 known forces: electromagnetic, weak, strong, gravitational
Nuclear Fusion• When 1,000 grams of
hydrogen are converted into 993 grams of helium, the 7 grams of mass left over is equivalent to the energy of 200 tons of coal!
• The Sun converts over 600 million tons of hydrogen into helium every second, and 22 million tons of mass are converted into energy.
Energy Generation in the Sun: The Proton-Proton Chain
Basic reaction:
4 1H 4He + energy
4 protons have 0.048*10-27 kg (= 0.7 %) more mass than 4He.
Energy gain = m*c2
= 0.43*10-11 J
per reaction.
Need large proton speed ( high temperature) to overcome
Coulomb barrier (electromagnetic repulsion between protons).
T ≥ 107 K = 10 million K
Daily Grade 11 – Question 3
How does the sun maintain its energy output?
A. Gravitational contraction.
B. Fusion of hydrogen nuclei.
C. The impact of small meteoroids.
D. Fission of Uranium 235.
Energy Transport
• It takes nearly a million years for a photon of light to make its way from the core to the Sun's surface.
• The energy is radiated from the core to near the surface in a random walk fashion, then it is transported by convection to the surface.
• The tops of the convection cells are seen as solar granules.
• After reaching the photosphere, it is radiated through interplanetary space and beyond.
• Then it only takes 8.3 minutes to reach the Earth.
Probing The Solar Interior
• Solar Seismology
• Solar Neutrinos
Helioseismology
• The Sun vibrates at a number of different frequencies - sun quakes.
• Because the vibrations are effected by its internal structure, solar oscillations can be used to study the Sun's interior.
The solar interior is opaque (i.e. it absorbs light) out to the photosphere.
Only way to investigate solar interior is through Helioseismology
= analysis of vibration patterns visible on the solar surface:
Approx. 10 million wave
patterns!
Helioseismology
• Early studies have already found large convection layers and internal rotation rates.
• Global Oscillation Network Group (GONG) is a network of world wide solar oscillation observatories.
Daily Grade 11 – Question 4
How are astronomers able to explore the layers of the sun below the photosphere?
A. Short wavelength radar pulses penetrate the photosphere and rebound from deeper layers within the sun.
B. Long wavelength radar pulses penetrate the photosphere and rebound from deeper layers within the sun.
C. Highly reflective space probes have plunged below the photosphere and sampled the sun's interior.
D. By measuring and modeling the modes of vibration of the sun's surface.
The Solar Neutrino Problem
Davis solar neutrino experiment
• The solar interior can not be observed directly because it is highly opaque to radiation.
• But neutrinos can penetrate huge amounts of material without being absorbed.
• Theory predicts that these particles should be leaving the solar core and radiating into space.
• A number of neutrino detector experiments have been constructed in an attempt to measure these elusive particles.
• Early solar neutrino experiments detected a much lower flux of neutrinos than expected (the “solar neutrino problem”).
Solar Neutrino Results• Neutrinos come in three
“flavors”, but until recently we could only detect electron neutrinos.
• Recent results have proven that neutrinos change (“oscillate”) between different types (“flavors”).
• Electron neutrinos are produced in the high numbers that the existing model of solar activity predicts, but about two-thirds of them change somewhere en route from the Sun, morphing into some combination of the two other neutrino types, thus solving the solar neutrino problem.
For Next Time
• Read Units 52, 54, 56, and 58.