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Visible Image of the Sun

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The 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 ... – PowerPoint PPT presentation

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Title: Visible Image of the Sun


1
The 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.

2
Pressure (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?
3
Main Regions of the Sun
4
Solar 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
5
Luminosity 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)
6
How do we know the interior structure of the Sun?
7
The Standard Solar Model
8
Energy 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

9
Convection
  • 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

10
Solar 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).

11
The 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.
12
Chromosphere
13
Chromosphere (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

14
Chromospheric Spicules warm jets of matter
shooting out at 100 km/s last only
minutes Spicules are thought to the result of
magnetic disturbances
15
Transition Zone and Corona
16
Transition 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)
17
Corona (seen during full Solar eclipse)
Hot coronal gas escapes the Sun ? Solar wind
18
Solar Wind
19
Solar 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.

20
Hot coronal gas (1,000,000 K) emits mostly in
X-rays.
Coronal holes are related to the Suns magnetic
field
21
The 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).
22
Sunspots
Granulation around sunspot
23
Sunspots
  • 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)

24
Sunspots 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

25
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26
The 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
27
Solar 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)
28
Heating 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.

29
Charged particles follow magnetic fields between
sunspots Solar Prominences
Sunspots are cool, but the gas above them is hot!
30
Solar Prominence
Typical size is 100,000 km May persist for days
or weeks
31
Very large solar prominence (1/2 million km
across base, i.e. 39 Earth diameters) taken from
Skylab in UV light.
32
Solar 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
33
Coronal activity increases with the number of
sunspots.
34
What makes the Sun shine?
35
But 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!

36
But 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.

38
The 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.
39
Detecting 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)
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