a105 stars and galaxies
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A105 Stars and Galaxies. News Quiz Today Review Exam 1 Homework 6 (the Sun) due Thursday. Today’s APOD. Announcements…. Solar Lab today at 11, tomorrow at 2 PM Kirkwood Obs. Moon Festival, Oct. 4, 8:30-10:30 Rooftop Session, Oct. 4, 9:00 - PowerPoint PPT PresentationTRANSCRIPT
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A105 Stars and Galaxies
News Quiz Today Review Exam 1 Homework 6 (the Sun) due Thursday
Today’s APOD
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Announcements…• Solar Lab today at 11, tomorrow at 2
PM• Kirkwood Obs. Moon Festival, Oct. 4,
8:30-10:30• Rooftop Session, Oct. 4, 9:00• Orionid meteor shower, Oct. 21-22, just
before midnight
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Exam Review• Range of score: 24-76 of 80 questions
• Average score: 54/80
NovaSearch I Homework• If you picked a year with just a few observations
available, you will need to select another year with more for NS II and NS III!
• If the year you selected did not seem to show any blemishes, view some other years to see what they look like.
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News Quiz• On a piece of paper, list three
important ideas from this week’s audio selection
• Print your name carefully – if we can’t read your writing, we can post the points to the gradebook!
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The Sun Today• Image credit:
Solar Orbiting Heliospheric Observatory/MDI
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Basic Facts• radius
• 7 x 105 km• about 100 x Earth’s radius
• mass = about 300,000 x Earth’s mass
• distance • 1 AU, 8 light minutes• 1.5 x 108 km• about 100 x Sun’s diameter
• Temperature• about 6000 Kelvin (10,000 F) at the surface• about 15 million Kelvin inside
• Composition • 90% of atoms are hydrogen• 10% of atoms are helium
WHY WE STUDY THE SUN
The Sun
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Helioseismology
With helioseismology, we can measure temperature, pressure and motion inside the Sunfrom sound waves thattraverse the Sun’s interior.
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Listen to the Sun
The Sun oscillates in complex patterns over the whole interior and surface. The frequency
and location of the oscillations give us a detailed picture of the inside of the Sun.
Helioseismology
blue = inward motion
red = outward motion
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Basic Structure
INSIDECore
Radiative ZoneConvection Zone
OUTSIDEPhotosphere
ChromosphereCorona
Solar Wind
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Conditions inside the Sun
Temperature peaks in the core and drops off at the
outside edge of the Sun
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Why does the Sun Shine?
• The Sun is a “cooling ember”
• The Sun is burning like coal or wood
• The Sun is contracting due to gravity
NONE OF THESE PRODUCES ENOUGH ENERGY
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NUCLEAR REACTIONS produce enough energy
Luminosity~ 10 billion years
Nuclear Potential Energy (core)
E = mc2
- Einstein, 1905
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Fission:Big nucleus splits into smaller pieces
Fusion:Small nuclei stick together to make a bigger one
What produces nuclear energy?
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The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus
Nuclear fusion requires high temperatures and high density
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The Sun’s Energy Comes from Nuclear Fusion
The Conversion of hydrogen into helium
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Proton-proton chain fuses hydrogen into helium
IN: 4 protons
OUT:4He nucleus
2 gamma rays2 positrons2 neutrinos
Total mass is 0.7% lower
•The missing mass is converted to energy•Rate of nuclear fusion depends on temperature
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•Neutrinos created during fusion fly directly out of the Sun•These neutrinos can be detected on Earth
How do we know nuclear reactions are going on in the Sun?
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Estimating the Sun’s Lifetime
• How much fuel does the Sun have?• How fast is that fuel being consumed?• When will it run out?
The Sun’sLifetime
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How much fuel?
• The Sun “burns” hydrogen to helium in a nuclear reaction
• How many hydrogen atoms in the Sun– 2 x 1033 grams of hydrogen– 6 x 1023 atoms in each gram
E = mc2
12 x 10 56 hydrogen atoms
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How Much Energy Can the Sun Produce?
• For each helium nucleus created, the Sun produces 5 x 10-12 joules of energy– the Sun can burn half its hydrogen– FOUR hydrogen atoms are needed to make
each helium atom
E = mc2
½ x ¼ x 12x1056 x 5x10-12
= 7 x 10 44 joules
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• How Much Energy Each Second? – At the distance of the Earth,
the Sun radiates 1400 watts (1400 joules per second) in each square meter on the surface of a sphere with a radius equal to one AU
– How many square meters are on that sphere?
The Solar Constant
1 meter
1400 watts =14 100-watt light bulbsWhat is a joule?
Each second a 100-wattlight bulb produces 100 joules of energy
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Sphere with radius of 1 AU Surface area of
a sphere
= 4r2
How many square meters on a sphere with radius one AU?
Area times energy per square meter per second equals total energy outputper second
The Sun produces4 x 1026 watts
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Solar Energy
From the conversion of hydrogen into helium by nuclear reactions… E = mc2
How long will the Sun shine???
Total energy available = 7 x 1044 joules
Radiating energy at 4 x 1026 joules per second
Lifetime = 7 x 1044 joules 4 x 1026 joules per second
= 2 x 1018 seconds = 6 x 1010 years
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Solar Energy
In fact, the Sun will only shinefor about 10 billion years, twiceits present age.
E = mc2
How long will the Sun shine???
Not all the Sun’s hydrogen is in regionshot enough for hydrogen fusion reactionsto occur.
We’ll learn more about the futureevolution of the Sun as we look more closely at other stars in the Galaxy.
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• Radiation
• Convection
How does the energy from fusion get out of the Sun?
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How does the energy from fusion get out of the Sun?
Radiation: In the inner regions of the solar interior, energy gradually leaks upward in form of randomly bouncing electromagnetic waves.
Further from the center, the wavelengths of the electromagnetic waves become longer.
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Energy Transport
In the outer regions of the Sun’s interior, energy flows outward by convection; heat is carried upward by bubbling hot gas.
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The convection zone gives the surface the appearance of boiling liquid
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Gravitational contraction:
Provided energy that heated core as Sun was forming
Contraction stopped when fusion began
Gravitational equilibrium:Energy provided by fusion maintains the pressure
Balancing Gravity
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Solar Thermostat
Decline in core temperature causes fusion rate to drop, so core contracts and heats up
Rise in core temperature causes fusion rate to rise, so core expands and cools down
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Summary:
• Why was the Sun’s energy source a major mystery?– Chemical and gravitational energy sources
could not explain how the Sun could sustain its luminosity for more than about 25 million years
• Why does the Sun shine?– The Sun shines because gravitational
equilibrium keeps its core hot and dense enough to release energy through nuclear fusion.
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The Budget of Solar Radiation
percent
Reflected back out to space 35%
Absorbed by atmosphere 18%
Scattered to the Earth from blue sky 10%
Scattered to the Earth from clouds 14%
Hits the Earth's surface directly 23%
100%
What happens to sunlight that falls on the Earth?
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Recall the structure of the Sun…
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Corona
The Sun’s Atmosphere: Photosphere, Chromosphere, Corona, Solar Wind
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The Sun! Units 49, 50, 52 Homework 6 Due THURS.
SOLAR LAB TODAY AT 11:00,TOMORROW AT 2:00