Title: The Sun
1The Sun
- Astronomy 311
- Professor Lee Carkner
- Lecture 23
2Helios -- The God of the Sun
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- The Sun was often worshiped by ancient people
3WARNING !
- NEVER LOOK DIRECTLY AT THE SUN
- NEVER LOOK AT THE SUN WITH BINOCULARS OR A
TELESCOPE - PERMANENT EYE DAMAGE CAN RESULT
4Observing the Sun
- With a solar filter in place we can use a
telescope to get a high spatial resolution
optical image of the Sun -
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5Todays Sun
6The Sun From the Inside Out
- We will examine the Sun from the core to the
diffuse outer layers -
- Nuclear fusion and magnetic fields play key roles
in the energetics and structure of the Sun
7Why Does the Sun Shine?
- From radioisotope dating we know that the solar
system is 4.5 billion years old - What could power the Sun for this length of time?
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8The Core
- At the core of the Sun the temperature and
pressure are very high due to the weight of the
outer layers -
- At these conditions the hydrogen atoms are moving
so fast and are packed together so tightly that
they can fuse together to make helium -
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9Hydrogen Fusion
10How Does the Energy at the Core Get Out?
- In general energy is transported in 3 ways
- Conduction --
- Radiation --
- Convection --
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11The Inner Structure of the Sun
12Radiative and Convective Zones
- Radiative Zone (0.25-0.71 Rsun)
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- Convective Zone (0.71-1.00 Rsun)
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- Hot material rises causing convection
13The Photosphere
- It takes about 170,000 years for the energy to
reach the surface of the Sun -
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- The photosphere has an average temperature of
5800 K -
- The top layer will absorb some of the light from
the bottom layers producing absorption lines
14Granulation in the Photosphere
- The photosphere is at the top of the convective
zone -
- The photosphere is covered with granules (each
about 1000 km across) -
15Solar Granulation
16Granules
17Sunspots in the Photosphere
- The photosphere sometimes has small dark regions
called sunspots -
- Sunspots are regions where the Suns magnetic
field inhibits the flow of warmer material
18Sunspots
19Sunspot Cycles
- Sunspots exist for a maximum of a few months
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- There is a sunspot cycle of 11 years
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- The sunspots move towards the equator over the
course of the cycle -
20Sunspot Maximum and Minimum
21The Sunspot Cycle
22Sunspot Cycles and Differential Rotation
- The Sun rotates differentially
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- The magnetic field gets wrapped-up around the
equator -
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- The sunspots are caused by the magnetic field
kinks -
23The Twisted Magnetic Field of the Sun
24The Suns Magnetic Field
- The Suns magnetic field extends far out beyond
the surface -
- These loops can break and reconnect
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25The Chromosphere
- The chromosphere is a diffuse layer of the solar
atmosphere extending from the photosphere to
about 2000 km -
- It has a temperature of about 20000 K
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26The Structure of the Chromosphere
- The chromosphere is composed of many rising
filaments of hot gas called spicules -
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- Between the chromosphere and the corona is the
transition region where the temperature rises
from 20,000 K to 1 million K over a small region
27Spicules in the Chromosphere
28Temperature in the Suns Atmosphere
29The Corona
- The corona is the outer layer of the Suns
atmosphere -
- It is thinner and hotter than the chromosphere
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- The high temperatures produce a hot ionized gas
called a plasma -
30Flares and Magnetic Activity
- The material in the corona is constantly changing
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- Flare activity is linked to sunspot activity
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- Changes in magnetic activity seem to effect
climate -
31Magnetic Activity Cycle
32The Structure of the Corona
- The high temperatures and irregular structure of
the corona are due to magnetic fields -
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- The tangled, shifting magnetic loops gives the
corona its structure
33Structure of the Sun
Core Radiative Zone Convective Zone Photosphere Ch
romosphere Corona
34Summary Structure of the Sun
- Core
- fusion converts H to He and power the Sun
- Radiative Layer
- transports energy from the core
- Convective Layer
- transports energy to the photosphere
- Photosphere
- visible surface of the Sun
- Chromosphere
- hot middle atmospheric layer
- Corona
- very hot outer layer
35Summary Solar Energetics
- Thermonuclear Fusion
- Energy is produced at the core of the Sun by
converting hydrogen to helium - Energy Transport
- Energy is transported via radiation where the
opacity is low and via convection where the
opacity is high - Magnetic Fields
- The outer layers of the Sun are composed of hot
plasma in magnetic loops