Structure of the Sun

Mr. VillegasAstronomyHaltom HS

The Sun’s Energy

Section 1

Composition of the Sun

Using a device called a spectrograph, scientists break up the sun’s light into a spectrum.

Dark lines form in the spectra of stars when gases in the stars’ outer layers absorb specific wavelengths of the light that passes through the layers.

By studying the spectrum of a star, scientists can determine the amounts of elements that are present in a star’s atmosphere.

Composition of the Sun

Because each element produces a unique pattern of spectral lines, astronomers can match the spectral lines of starlight to those of Earth’s elements, and identify the elements in the star’s atmosphere.

Both hydrogen and helium occur in the sun. About 75% of the sun’s mass is hydrogen, and hydrogen and helium together make up about 99% of the sun’s mass.

The sun’s spectrum reveals that the sun contains traces of almost all other chemical elements.

Nuclear Fusion

Nuclear fusion occurs inside the sun.

Nuclei of hydrogen atoms are the primary fuel for the sun’s fusion.

Nuclear fusion produces most of the suns’ energy and consists of three steps.

Nuclear Fusion

In the first step, two hydrogen nuclei, or protons, collide and fuse. – In this step, the positive charge of one of the protons is

neutralized as that proton emits a particle called a positron.

As a result, the proton becomes a neutron and changes the original two protons into a proton-neutron pair.

Nuclear Fusion

In the second step, another proton combines with this proton-neutron pair to produce a nucleus made up of two protons and one neutron.

In the third step, two nuclei made up of two protons and one neutron collide and fuse.

As this fusion happens, two protons are released. The remaining two protons and two neutrons are fused together and form a helium nucleus. At each step, energy is released

Nuclear Fusion

The Final Product

One of the final products of the fusion of hydrogen in the sun is always a helium nucleus.

The helium nucleus has about 0.7% less mass than the hydrogen nuclei that combined to form it do. The lost mass is converted into energy during the series of fusion reactions that forms helium.

The energy released during the three steps of nuclear fusion causes the sun to shine and gives

Mass Changing into Energy

The sun’s energy comes from fusion, and the mass that is lost during fusion becomes energy.

In 1905, Albert Einstein proposed that a small amount of matter yields a large amount of energy.

This proposal was part of Einstein’s special theory of relativity.

This theory included the equation:

E = mc2

Mass Changing into Energy

In Einstein’s equation E = mc2, – E represents energy produced; – m represents the mass; – c represents the speed of light, which is about

300,000 km/s.

Einstein’s equation can be used to calculate the amount of energy produced from a given amount of matter.

Spot Question

How did the equation E = mc2 help scientists understand the energy of the sun?

Einstein’s equation helped scientists understand the source of the sun’s energy. The equation explained how the sun could produce huge amounts of energy without burning up.

The Core

The parts of the sun include the core, the radiative zone, and the convective zone.

At the center of the sun is the core. – The core makes up 25% of the sun’s total diameter of

1,390,000 km. – The temperature of the core is about 15,000,000

kmºC.

The core is made up entirely of ionized gas, and is 10 times as dense as iron.

The Radiative Zone

The radiative zone of the sun surrounds the core.

The temperature of the radiative zone ranges from about 2,000,000ºC to 7,000,000 ºC .

In the radiative zone, energy moves outward in the form of electromagnetic waves

The Convective Zone

The convective zone surrounds the radiative zone. – The temperature of the convective zone is

about 2,000,000ºC.

Energy produced in the core moves through this zone by convection.

Convection is the transfer of energy

The Sun

The Sun’s Atmosphere

The sun’s atmosphere surrounds the convective zone of the sun’s core.

Because the sun is made of gases, the term atmosphere refers to the uppermost region of solar gases.

The sun’s atmosphere has three layers: the photosphere, the chromosphere, and the corona.

The Photosphere

Photosphere means “sphere of light.” The photosphere of the sun is the innermost layer of the sun’s atmosphere. – It is the visible surface of the sun

The photosphere is made of gases that have risen from the convective zone. – The temperature in the photosphere is about 6,000ºC.

Much of the energy given off from the photosphere is in the form of visible light.

Spot Question

What layers make up the sun’s atmosphere?

The sun’s atmosphere consists of the photosphere, the chromosphere, and the corona.

The Chromosphere

The chromosphere lies just above the photosphere. – The chromosphere’s temperature ranges from

4,000°C to 50,000 °C.

Also known as the “Color Sphere”.

The Chromosphere

The Sun’s Outer Parts

The corona is a huge region of gas that has a temperature above 1,000,000ºC.

As the corona expands, electrons and electrically charged particles called ions stream out into space.

These particles make up solar wind, which flows outward from the sun to the rest of the solar system

Corona

Section 2 Solar Activity

Sunspots

Sunspot are dark area cooler areas of the photosphere

Magnetic fields cause convection to slow in parts of the convective zone.

This causes a less energy to go from the core to the photosphere.

Less energy makes these regions of the photosphere are considerably cooler.

Cooler areas appear darker than their surrounding regions.

The Sunspot Cycle

Observations of sunspots have shown that the sun rotates.

The numbers and positions of sunspots vary in a cycle that lasts about 11 years.

Sunspots initially appear in groups about midway between the sun’s equator and poles.

The # will peak at about 100 of more sunspots.

After the peak, the number of sunspots begins to decrease until it reaches a minimum

The Sunspot Cycle

Solar Ejections

The solar-activity cycle is caused by the changing solar magnetic field.

This cycle is characterized by increases and decreases in various types of solar activity, including solar ejections.

Solar ejections are events in which the sun emits atomic particles.

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Solar ejections include prominences, solar flares, and coronal mass ejections.

Prominences are huge arches of glowing gases that follow the curved lines of the magnetic force from a region of one magnetic force to a region of the opposite magnetic.

Solar Ejections: Solar Flares

Solar flares are the most violent of all solar disturbances.

Solar flares release the energy stored in the strong magnetic fields of sunspots

Solar Ejections: Coronal Mass Ejections

Some of the particles from a solar flare escape into space, increasing the strength of the solar wind.

Particles also escape as coronal mass ejections. The particles in the ejection can cause disturbances to Earth’s magnetic field.

These disturbances have been known to interfere with radio communications, satellites, and even cause blackouts

Auroras

Auroras are the result of the interaction between the solar wind and Earth’s magnetosphere.

Auroras are usually seen close to Earth’s magnetic poles because electrically charged particles are guided toward earth’s magnetic poles by Earth’s magnetosphere.

Auroras

Depending on the pole there are near they are called different things. North Pole= aurora borealis or northern light. South Pole= aurora australis or southern lights.

Auroras are most frequent just after peak sunspot cycles

In the United States auroras are visible about 5 times per year, however in Alaska auroras can be seen almost every clear night. Astronauts can even see auroras in orbit.