Title: Visible Image of the Sun
1The Sun
Visible Image of the Sun
- Our sole source of light and heat in the solar
system - A very common star a glowing ball of gas held
together by its own gravity and powered by
nuclear fusion at its center.
2Pressure (from heat caused by nuclear reactions)
balances the gravitational pull toward the Suns
center. Called Hydrostatic Equilibrium.
This balance leads to a spherical ball of gas,
called the Sun.
What would happen if the nuclear reactions
(burning) stopped?
3Main Regions of the Sun
4Solar Properties
Radius 696,000 km (100 times Earth) Mass 2
x 1030 kg (300,000 times Earth) Av. Density
1410 kg/m3 Rotation Period 24.9
days (equator) 29.8 days
(poles) Surface temp 5780 K
5Luminosity of the Sun LSUN
(Total light energy emitted per second)
4 x 1026 W 100 billion one-megaton nuclear
bombs every second!
Solar constant LSUN / 4?R2 (energy/second/area
at the radius of Earths orbit)
6How do we know the interior structure of the Sun?
7The Standard Solar Model
8Energy Transport within the Sun
- Extremely hot core - ionized gas
- No electrons left on atoms to capture photons -
core/interior is transparent to light (radiation
zone) - Temperature falls further from core - more and
more non-ionized atoms capture the photons - gas
becomes opaque to light in the convection zone - The low density in the photosphere makes it
transparent to light - radiation takes over again
9Convection
- Convection takes over when the gas is too opaque
for radiative energy transport. - Hot gas is less dense and rises (or floats,
like a hot air balloon or a beach ball in a
pool). - Cool gas is more dense and sinks
10Solar Granulation Evidence for Convection
- Solar Granules are the tops of convection cells.
- Bright regions are where hot material is
upwelling (1000 km across). - Dark regions are where cooler material is
sinking. - Material rises/sinks _at_ 1 km/sec (2200 mph
Doppler).
11The Solar Atmosphere
- The solar spectrum has thousands of absorption
lines - More than 67 different elements are present!
- Hydrogen is the most abundant element followed
by Helium (1st discovered in the Sun!)
Spectral lines only tell us about the part of the
Sun that forms them (photosphere and
chromosphere) but these elements are also thought
to be representative of the entire Sun.
12Chromosphere
13Chromosphere (seen during full Solar eclipse)
- Chromosphere emits very little light because it
is of low density - Reddish hue due to 3?2 (656.3 nm) line emission
from Hydrogen
14Chromospheric Spicules warm jets of matter
shooting out at 100 km/s last only
minutes Spicules are thought to the result of
magnetic disturbances
15Transition Zone and Corona
16Transition Zone Corona
Very low density, T 106 K
We see emission lines from highly ionized
elements (Fe5 Fe13) which indicates that the
temperature here is very HOT
- Why does the Temperature rise further from the
hot light source?
? magnetic activity -spicules and other more
energetic phenomena (more about this later)
17Corona (seen during full Solar eclipse)
Hot coronal gas escapes the Sun ? Solar wind
18 Solar Wind
19Solar Wind
- Coronal gas has enough heat (kinetic) energy to
escape the Suns gravity. - The Sun is evaporating via this wind.
- Solar wind travels at 500 km/s, reaching Earth
in 3 days - The Sun loses about 1 million tons of matter
each second! - However, over the Suns lifetime, it has lost
only 0.1 of its total mass.
20Hot coronal gas (1,000,000 K) emits mostly in
X-rays.
Coronal holes are related to the Suns magnetic
field
21The Active Sun
UV light
Most of theSolar luminosity is continuous
photosphere emission. But, there is an irregular
component (contributing little to the Suns
total luminosity).
22Sunspots
Granulation around sunspot
23Sunspots
- Typically about 10000 km across
- At any time, the sun may have hundreds or none
- Dark color because they are cooler than
photospheric gas (4500K in darkest parts)
- Each spot can last from a few days to a few
months - Galileo observed these spots and realized the
sun is rotating differentially (faster at the
poles, slower at the equator)
24Sunspots Magnetic Fields
- The magnetic field in a sunspot is 1000x greater
than the surrounding area - Sunspots are almost always in pairs at the same
latitude with each member having opposite
polarity - All sunspots in the same hemisphere have the same
magnetic configuration
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26The Suns differential rotation distorts the
magnetic field lines
The twisted and tangled field lines occasionally
get kinked, causing the field strength to increase
tube of lines bursts through atmosphere
creating sunspot pair
27Solar maximum is reached every 11 years
Solar Cycle is 22 years long direction of
magnetic field polarity flips every 11 years
(back to original orientation every 22 years)
28Heating of the Corona
- Charged particles (mostly protons and electrons)
are accelerated along magnetic field lines
above sunspots. - This type of activity, not light energy, heats
the corona.
29Charged particles follow magnetic fields between
sunspots Solar Prominences
Sunspots are cool, but the gas above them is hot!
30Solar Prominence
Typical size is 100,000 km May persist for days
or weeks
31Very large solar prominence (1/2 million km
across base, i.e. 39 Earth diameters) taken from
Skylab in UV light.
32Solar Flares much more violent magnetic
instabilities
5 hours
Particles in the flare are so energetic, the
magnetic field cannot bring them back to the Sun
they escape Suns gravity
33Coronal activity increases with the number of
sunspots.
34What makes the Sun shine?
35But where does the Energy come from?
- c2 is a very large number!
- A little mass equals a LOT of energy.
- Example
- 1 gram of matter ? 1014 Joules (J) of energy.
- Enough to power a 100 Watt light bulb for
32,000 years!
36But where does the Energy come from!?
The total mass decreases during a fusion reaction.
Mass lost is converted to Energy Mass of 4 H
Atoms 6.693 ? 10-27 kg Mass of 1 He Atom
6.645 ? 10-27 kg Difference
0.048 ? 10-27 kg ( m converted to E)
(0.7)
The sun has enough mass to fuel its current
energy output for another 5 billion years
37- Nuclear fusion requires temperatures of at
least 107 K why? - Atomic nuclei are positively charged ? they
repel via the electromagnetic force. - Merging nuclei (protons in Hydrogen) require
high speeds.
- (Higher temperature faster motion)
- At very close range, the strong nuclear force
takes over, binding protons and neutrons
together (FUSION). - Neutrinos are one byproduct.
38The energy output from the core of the sun is in
the form of gammy rays. These are transformed
into visible and IR light by the time they reach
the surface (after interactions with particles in
the Sun).
Neutrinos provide important tests of nuclear
energy generation.
39Detecting Solar Neutrinos these light detectors
measure photons emitted by rare chlorine-neutrino
reactions in the fluid.
Solar Neutrino Problem There are fewer observed
neutrinos than theory predicts (!) A discrepancy
between theory and experiments could mean we have
the Suns core temperature wrong. But probably
means we have more to learn about neutrinos!
(Neutrinos might oscillate into something else,
a little like radioactive decays)