Transcript 23sun6s
The Sun
Astronomy 311
Professor Lee Carkner
Lecture 23
What is responsible for creating a
comet’s tail?
a)
b)
c)
d)
e)
The solar wind
The comet’s motion
Light pressure
a and c only
a, b, and c
Which of the following would you
not expect to find in a comet?
a)
b)
c)
d)
e)
Ammonia
Carbon Dioxide
Iron
Silicates
Carbon compounds
If a comet is 30 AU from the sun,
what part would be most visible?
a)
b)
c)
d)
e)
Ion tail
Dust tail
Coma
Corona
Nucleus
Why does a given meteor shower
occur once per year?
a) One year is the period of the comet
b) The meteors disperse after one year
c) The comet debris occupies one spot
on the Earth’s orbit
d) It takes one year for the comet to
produce more debris
e) It is only one year for short period
comets, for long period comets the
showers happen every few years
Helios -- The God of the Sun
The Sun was often
worshiped by
ancient people
WARNING !
NEVER LOOK DIRECTLY AT THE
SUN
NEVER LOOK AT THE SUN WITH
BINOCULARS OR A TELESCOPE
PERMANENT EYE DAMAGE CAN
RESULT
Observing the Sun
The solar surface is nearly featureless
Much of our information about the Sun
comes from multiwavelength observations,
indirect measurements, and modeling
The Sun From the Inside Out
The solar interior is the source of solar
energy which is transported to the
surface
Nuclear fusion and magnetic fields
play key roles in the energetics and
structure of the Sun
Why Does the Sun Shine?
What could power the Sun for this length of
time?
Chemical energy (burning) -Kelvin-Helmholtz contraction (gravitational
energy) -Nuclear Fusion Reactions --
The 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:
Each reaction converts some mass to energy
(E=mc2)
Hydrogen Fusion
How Does the Energy at the
Core Get Out?
Energy in the Sun is transported in two ways:
Radiation -Like a heat lamp
Gas in this area is very hot and ionized and so
doesn’t absorb the radiation very well
Convection --
Like baseboard heating
Cooler outer layers are less ionized and so absorb
the radiation and heat up and rise
The Inner Structure of the Sun
The Photosphere
It takes about 170,000 years for the energy to reach
the surface of the Sun
The visible surface of the Sun is called the
photosphere
The photosphere is the top of the convection zone
The surface of the sun is covered in granules where hot gas
from the interior of the Sun is rising
Each about 1000 km across
Granules
Sunspots in the Photosphere
The photosphere sometimes has small
dark regions called sunspots
Sunspots are regions where the Sun’s
magnetic field inhibits the flow of
warmer material
Sunspots
Sunspot Cycles
Sunspots exist for a maximum of a few months
There is a sunspot cycle of 11 years
The year 2000 was a sunspot maximum
Just after sunspot minimum the spots appear at about
30 degrees north or south
Sunspot Maximum and
Minimum
The Sunspot Cycle
Sunspot Cycles and
Differential Rotation
The Sun rotates differentially
The magnetic field gets “wrapped-up” around the
equator
Eventually the magnetic field is squeezed so tight it
reconnects and cancels itself out
The magnetic field prevents warmer material from
flowing into the sunspots, so the sunspots are cooler than
the rest of the photosphere
The Twisted Magnetic Field of
the Sun
The Sun’s Magnetic Field
It is twisted and tangled producing loops of
magnetic force
The Sun’s magnetic field is responsible for
the structure and heating of the outer layers
of the atmosphere
The Solar Wind
This flow of charged particles is called the solar
wind
Interacts with the Earth’s magnetic field
Very strong solar wind bursts can cause
power and communication failures
The Chromosphere
It has a density of 1/10000 of the photosphere so it
is hard to see
It has a temperature of about 20000 K
It is too thin for the atoms to collide and lose energy
The Corona
The corona is the outer layer of the Sun’s
atmosphere
It is thinner and hotter than the chromosphere
The high temperatures produce a hot ionized
gas called a plasma
This plasma emits strongly at ultraviolet and
X-ray wavelengths
Flares and Magnetic Activity
Sometimes a large outburst of material is seen,
called a coronal mass ejection
They are both examples of magnetic activity
During the Maunder Minimum in sunspot activity
(1645-1715) it was very cold in Europe (The Little Ice
Age)
Core
Radiative Zone
Convective Zone
Photosphere
Chromosphere
Corona
Structure of the Sun
Summary: 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
Summary: 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