Download The Sun - the University of Redlands

THE SUN
The star we see by day
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The Sun, Our Star
• The Sun is an average star.
• From the Sun, we base our understanding of all
stars in the Universe.
• No solid surface.
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Interior Properties
• Core = 20 x density of iron
• Surface = 10,000 x less dense
than air
• Average density = Jupiter
• Core = 15,000,000 K
• Surface = 5800 K
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Scientific Method
• How do we know this stuff?
• Three examples:
– Fusion in the core (core temperature).
– Different zones in interior.
– Solar activity and Earth
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1. The Core
• Scientific Method:
– Observations
– Make hypothesis (a model)
• Models make predictions
– Test predictions
• Compare results of predictions with observations
– Revise model if necessary.
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Testing the Core
• Observe Sun’s:
– Mass (how?)
– Composition (how?)
– Radius
• Use physics to make a model Sun.
• Predict:
– Surface temp/density (how do you test?)
– Surface Luminosity (how do you test?)
– Core temp/density  Fusion Rate  neutrino rate (test?)
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In The Core
• Density = 20 x
density of Iron
• Temperature =
15,000,000 K
• Hydrogen atoms
fuse together.
• Create Helium
atoms.
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2. Helioseismology
• Continuous monitoring of
Sun.
– Ground based observatories
– One spacecraft (SOHO)
• Surface of the Sun is
‘ringing’
• Sound waves cross the the
solar interior and reflect off
of the surface
(photosphere).
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Solar Interior
• Core
– Only place with
fusion
• Radiation Zone
– Transparent
• Convections Zone
– Boiling hot
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Convection
•
•
•
•
A pot of boiling water:
Hot material rises.
Cooler material sinks.
The energy from the pot’s
hot bottom is physically
carried by the convection
cells in the water to the
surface.
• Same for the Sun.
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Solar Cross-Section
• Progressively smaller
convection cells carry the
energy towards surface.
• See tops of these cells as
granules.
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The Photosphere
• This is the origin of the 5,800 K thermal radiation we
see.
l = k/T = k/(5800 K)  l = 480 nm (visible light)
• This is the light we see.
• That’s why we see this as the surface.
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3. Solar Activity and Earth
• Is there a connection between Solar Activity and
Earth’s Climate?
• Observation:
– Little Ice Age
– Maunder Minimum
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What is Solar Activity?
•
•
•
•
•
•
•
Sunspots
Magnetic Fields
Coronal Mass Ejections
Solar Wind
Magnetic Storms
Aurora
Other effects?
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•
•
•
•
11-year sunspot cycle.
Center – Umbra: 4500 K
Edge – Penumbra: 5500 K
Photosphere: 5800 K
Sunspots
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Magnetic fields and Sunspots
• At kinks, disruption in convection cells.
• Sunspots form.
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Magnetic fields and Sunspots
• Where
magnetic
fields “pop
out” of Sun,
form sunspots.
• Sunspots
come in pairs.
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Prominences
Hot low density gas = emission lines
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Corona and Solar Wind
• Hot, low density, gas emits the radiation we see as
the Corona: 1,000,000 K
• Solar Wind: Like steam above our boiling pot of
water, the gas ‘evaporates’.
• Carries away a million tons of Sun’s mass each
second!
• Only 0.1% of total Sun’s mass in last 4.6 billion
years.
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Solar Cycle
• Increase in solar wind activity
- Coronal Mass Ejections
• Increase in Auroral displays on Earth
• Increase in disruptions on and around Earth.
Courtesy of SOHO/LASCO/EIT consortium.
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Aurora
• The solar wind
passes out
through the
Solar System.
• Consists of electrons, protons and other charged particles
stripped from the Sun’s surface.
• Magnetic fields herd charged particles into atmosphere at poles.
• Charged particles excite electrons in atoms.  Light!
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2003 CME
Oklahoma 10/29/2003
Credit: E. Woldt
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Homework #7
•
Due Monday 30-Jan, Read Exoplanet articles
plus the website:
• http://www.howstuffworks.com/planethunting2.htm
Why do we believe there are planets around other
stars? How have we detected them?
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