Download Layers of the Sun (~ 75% Hydrogen ~ 25% Helium)

Astronomy – The Sun – Definitions & Notes
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The Sun is mostly made of Hydrogen and Helium. On Earth H and He is a gas.
However, on the Sun, pressures are so great that it turns H and He into a liquid, and then
into a Solid. However, toward the surface of the sun, H and He are still gasses. This is
the Suns atmosphere.
Atmosphere of the Sun: 3 layers:
Photosphere, Chromosphere, Corona
1. Photosphere (Light Layer) (6,000°C (11,000°F)
The visible surface of the Sun. It consists of a zone in which the gaseous layers
change from being completely opaque to radiation to being transparent. It is the
layer from which the light we actually see (with the human eye) is emitted. This
layer is very thin, ~ 500 km deep.
Features:
Sunspots: Dark, cool magnetic storms. Usually larger than the size of
earth.
Granules: A roughly circular region on the Sun whose bright center
indicates hot gases rising to the surface, and whose dark edges indicate
cooled gases that are descending towards the interior. Individual granules
appear and disappear on time scales of about 5 minutes and are typically
about 1000 km.
2. Chromosphere (Color layer)
A very thin layer of the solar atmosphere that is located above the photosphere
and beneath the corona. The chromosphere is hotter than the photosphere but not
as hot as the corona. The temperature ranges from 6,000 °C (at lower altitudes) to
50,000 °C (at higher altitudes). This layer is a few thousand miles (or kilometers)
thick. It appears red because hydrogen atoms are in an excite state and emit
radiation near the red part of the visible spectrum.
Features: Spicules - flame-like jets of gas.
The Chromosphere is visible during solar eclipses (when the moon blocks the
Photosphere).
3. Corona (1,000,000 – 2,000,000 C) (~2,000,000 – 3,600,000 F)
The outermost layer of the solar atmosphere. The corona consists of a highly
rarefied (like a vacuum on earth) gas with a temperature greater than one million
degrees Kelvin. It is visible to the naked eye during a solar eclipse. The gas is
ionized. This ionized gas loops in massive magnetic fields, causing it to heat up.
The corona extends for millions of miles, up to 20 Sun diameters (28 million km,
roughly half the distance to mercury).
The corona can be seen during solar eclipses.
Astronomy – The Sun – Definitions & Notes
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Layers of the Sun (~ 73% Hydrogen ~ 25% Helium)
Core, Radiative Zone, Convective Zone
Core (15,000,000° C; 27,000,000° F)
In solar astronomy, the innermost part of the Sun, where energy is generated by
nuclear reactions (fusion).
The Sun's core has a tremendously high temperature and pressure. The
temperature is roughly 15 million °C. At this temperature, nuclear fusion occurs,
turning four hydrogen nuclei into a single helium nucleus plus a LOT of energy.
This "hydrogen burning" releases gamma rays (high-energy photons) and
neutrinos (particles with no charge and almost no mass).
Solar energy is created deep within the core of the Sun. It is here that the
temperature (15,000,000° C; 27,000,000° F) and pressure (340 billion times
Earth's air pressure at sea level) is so intense that nuclear reactions take place.
This reaction causes four protons or hydrogen nuclei to fuse together to form one
alpha particle or helium nucleus. The alpha particle is about .7 percent less
massive than the four protons. The difference in mass is expelled as energy and is
carried to the surface of the Sun, through a process known as convection, where it
is released as light and heat. Energy generated in the Sun's core takes a million
years to reach its surface. Every second 700 million tons of hydrogen are
converted into helium ashes. In the process 5 million tons of pure energy is
released; therefore, as time goes on the Sun is becoming lighter.
The Radiative Zone (or radiation zone): The next layer out from the core is this zone
which emits radiation. This radiation diffuses outwards. The temperature ranges
from 15 million °C to one million °C. It may take photons of radiation millions of
years to pass through the radiative zone, as they gradually make their way
outwards.
The Convective Zone: In this next layer, photons continue to make their way outwards
via convection (towards lower temperature and pressure). The temperature ranges
from one million °C to 6,000 °C.
In this layer of a star in which convection currents are the main mechanism by
which energy is transported outward. In the Sun, a convection zone extends from
just below the photosphere to about seventy percent of the solar radius. In the
convection zone, hot plasma rises, cool plasma sinks and eventually becomes
reheated.
Astronomy – The Sun – Definitions & Notes
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Definitions for activity on the Sun:
Granule
A roughly circular region on the Sun whose bright center indicates hot gases
rising to the surface, and whose dark edges indicate cooled gases that are
descending towards the interior. Individual granules appear and disappear on time
scales of about 5 minutes and are typically about 1000 km.
Sunspot
A temporary disturbed area in the solar photosphere that appears dark because it
is cooler than the surrounding areas. Sunspots consist of concentrations of strong
magnetic flux. They usually occur in pairs or groups of opposite polarity that
move in unison across the face of the Sun as it rotates.
Zeeman Effect
A splitting of spectral lines in response to a magnetic field. It is used to measure
magnetic field strengths on the Sun and on other astronomical objects.
Solar Cycle
The approximately 11-year quasi-periodic variation in frequency or number of
sunspots, coronal mass ejections, solar flares, and other solar activity. Sunspots
have an 11 year cycle. Each sunspot maximum occurs roughly every 11 years.
Maunder Minimum
A period of time between 1645 and 1715 of reduced solar activity. During this
time period there were little to no recorded sunspots. Accompanied by this were
unusually cool temperatures on earth. Glaciers began advancing, lakes and rivers
in northern Europe remained frozen year round.
Prominence
An arc of plasma trapped in the suns magnetic field lines. If the field lines
break, the plasma will be released into space, as a solar storm (CME or flare)
Coronal Mass Ejection (CME)
A huge magnetic bubble of plasma that erupts from the Sun's corona and travels
through space at high speed. Speeds range from 200 km/s to over 1000 km/s
Flare (Solar)
Rapid release of energy from a localized region on the Sun in the form of
electromagnetic radiation, energetic particles, and mass motions.
Solar Wind
A stream of particles, primarily electrons and protons, flowing outward from the
Sun at speeds as high as 900 km/s. The solar wind is essentially the hot solar
corona expanding into interplanetary and interstellar space
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Aurora:
A display of colored light given off by collisions between charged particles
trapped in a planet's magnetic fields and atoms of atmospheric gases near the
planet's magnetic poles. Aurora are visible on Earth as the aurora borealis or
northern lights and the aurora australis or southern lights.
The Earth’s magnetic field protects us from most solar radiation. The earths
magnetic field comes from our core, and exits our earth around the poles.
Charged particles from the sun can become trapped in our field, and follow the
field lines into our poles. When the particles hit our atmosphere near the poles, we
see a light display known as Aurora.
Large solar storms can overcharge satellites and power grids, causing damage to
them.
Plasma
Plasma consists of a gas heated to sufficiently high temperatures that the atoms
ionize. The properties of the gas are controlled by electromagnetic forces among
constituent ions and electrons, which results in a different type of behavior.
Plasma is often considered the fourth state of matter (besides solid, liquid, and
gas). Most of the matter in the Universe is in the plasma state.
Differential Rotation
The change in solar rotation rate with latitude. Low latitudes rotate at a faster
angular rate (approx. 14 degrees per day) than do high latitudes (approx. 12
degrees per day).
The Core
Fusion
The process that powers the Sun is called fusion. It works by turning mass into energy.
The center of the Sun is extremely hot (around 15,000,000 degrees), so hot that all the
atoms lose their electrons and become ions. It is also hot enough that the ions can
overcome their mutual electric repulsion and come close enough to join together.
If you measure the mass of the atoms before they come together and compare it to the
mass after they fuse then you find that there is less mass after than before. The mass
difference has been converted into energy according to Einstein's equation. This energy is
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carried away by photons and neutrinos. It is these photons that can eventually shine on
Earth.
Hydrostatic Equilibrium
Within the Sun, pressure from Fusion creates an outward force. Gravity creates an
inward force. When the force due to pressure exactly balances the force due to gravity, a
system (the sun) is in hydrostatic equilibrium.
Fusion vs. Fission:
Fusion is the combination of atomic nuclei into heavier atomic nuclei.
When fusion occurs, mass is lost in the reaction. This missing mass has been converted
into energy.
Fission is the splitting of atomic nuclei into smaller nuclei.
Nuclear reactors on earth use Fission. We cannot sustain fusion enough to be used on
earth yet.
During fission, when atoms are split, the split up atoms remain as nuclear waste.
Fusion produces no nuclear waste, and is much more energy efficient than fission.
Fusion occurs in the core of stars, including the Sun.
Proton-Proton chain:
Fusion in the sun is a 3 step process.
1)
1
H + 1H  2H + e+ + v
2)
2
H + 1H  3He + γ
3)
3
He + 3He  4He + 1H + 1H
1.) For step 1, regular Hydrogen combines with another Hydrogen. This produces a
Hydrogen with 2 protons in the nucleus (2H). It also produces energy. This energy is
in the form of a positron and a neutrino.
A positron (e+ ) is antimatter, it is the opposite of an electron. This positron will
combine with an electron. When they combine, they cancel out, and produce energy.
A neutrino (v) is a tiny, almost mass less particle (much less mass than even an
electron). Since a neutrino is so small, it will leave the sun unimpeded, and go into
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space. It will travel through space unimpeded. 1012 neutrinos from the sun pass
through our bodies unimpeded each second.
2.) For step 2, a heavy hydrogen (2H) will fuse with another regular hydrogen (H).
This will produce tritium, or a light helium atom (3He) and energy in the form of
gamma rays.
A gamma ray (γ) is one of the most energetic photons. The energy from gamma rays
heat up the core of the sun.
3.) For step 3, two light helium atoms (3He) will fuse together to produce a regular
helium atom (4He) and 2 hydrogen atoms (H). For step 3 to occur, steps 1 and 2
must be done twice. The excess 2 hydrogen atoms are then used for step 1, and the
cycle repeats.
The proton-proton chain ultimately fuses hydrogen into helium and releases energy.
Roughly, 5,000,000,000 tons of mass is converted into energy each second in the core
of the sun.
Eventually, the sun’s core will run low on H, and have an abundance of He. When
this occurs, the core will begin fusing He into heavier and heavier elements, such as
Li, B, C, N, and O.
Therefore, the cores of stars produce almost all of the elements found on the periodic
table of elements.
When a star dies, it explodes, and releases all of the elements it has created into the
universe.
In the early universe there was only H . When stars began forming and dying, other
elements were dispersed into the universe. The earth, and other terrestrial planets are
made almost entirely of heavier elements than H and He, and therefore came from the
core of a star that exploded long ago. This will be discussed in greater detail when we
look at planetary formation.