Objectives • Explore the structure of the Sun. The Sun • Describe the solar activity cycle and how the Sun affects Earth. • Compare the different types of spectra. – photosphere – chromosphere – corona – solar wind – sunspot Vocabulary – solar flare – prominence – fusion – fission – spectrum
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Objectives Explore the structure of the Sun. The Sun Describe the solar activity cycle and how the Sun affects Earth. Compare the different types of spectra.
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Objectives• Explore the structure of the Sun.
The Sun
• Describe the solar activity cycle and how the Sun affects Earth.
The Sun’s Atmosphere• The chromosphere, which is above the
photosphere and approximately 2500 km in thickness, has a temperature of nearly 30 000 K at the top.
The Sun
• The corona, which is the top layer of the Sun’s atmosphere, extends several million kilometers southward from the top of the chromosphere and has a temperature range of 1 million to 2 million degrees K.
– Gas flows outward from the corona at high speeds and forms the solar wind.
– Solar wind consists of charged particles, or ions, that flow outward through the entire solar system, bathing each planet in a flood of particles.
– The charged particles are trapped in two huge rings in Earth’s magnetic field, called the Van Allen belts, where they collide with gases in Earth’s atmosphere, causing an aurora.
– Coronal holes, often located over sunspot groups, are areas of low density in the gas of the corona.
– Solar flares are violent eruptions of particles and radiation from the surface of the Sun that are associated with sunspots.
– When these particles reach Earth, they can interfere with communications and damage satellites.
– A prominence, sometimes associated with flares, is an arc of gas that is ejected from the chromosphere, or gas that condenses in the inner corona and rains back to the surface.
– Some scientists have found evidence of subtle climate variations within 11-year periods.
– There were severe weather changes on Earth during the latter half of the 1600s when the solar activity cycle stopped and there were no sunspots for nearly 60 years.
– Those 60 years were known as the “Little Ice Age” because the weather was very cold in Europe and North America during those years.
– Energy produced in the core of the Sun gets to the surface through two zones in the solar interior.
• In the radiative zone, which is above the core, energy is transferred from particle to particle by radiation, as atoms continually absorb energy and then re-emit it.
• Above the radiative zone, in the convective zone, moving volumes of gas carry the energy the rest of the way to the Sun’s surface through convection.
Spectra• A spectrum is visible light arranged according
to wavelengths.
The Sun
• There are three types of spectra:– A continuous spectrum is a spectrum that has no breaks
in it that can be produced by a glowing solid or liquid, or by a highly compressed, glowing gas.
– An emission spectrum has bright lines in it called emission lines that depend on the element being observed.
– An absorption spectrum has dark lines called absorption lines which are caused by different chemical elements that absorb light at specific wavelengths.
Spectra• Absorption is caused by a cooler gas in front of a
source that emits a continuous spectrum.
The Sun
• By comparing laboratory spectra of different gases with the dark lines in the solar spectrum, it is possible to identify the elements that make up the Sun’s outer layers.
SpectraA continuous spectrum is produced by a hot solid, liquid, or dense gas. When a cloud of gas is in front of this hot source, an absorption spectrum is produced. A cloud of gas without a hot source behind it will produce an emission spectrum.
2. How can we determine what gases are in the outer layers of the Sun’s atmosphere?
The Sun
Dark bands in the solar spectrum represent light that has been absorbed by the gases of its atmosphere. By comparing laboratory spectra of different gases with the dark lines in the solar spectrum, it is possible to identify the elements that make up the Sun’s outer layers.
Groups of Stars• Constellations are the 88 groups of stars
named after animals, mythological characters, or everyday objects.
Measuring the Stars
– Circumpolar constellations can be seen all year long as they appear to move around the north or south pole.
– Summer, fall, winter, and spring constellations can be seen only at certain times of the year because of Earth’s changing position in its orbit around the Sun.
– Although stars may appear to be close to each other, very few are gravitationally bound to one other.
– By measuring distances to stars and observing how they interact with each other, scientists can determine which stars are gravitationally bound to each other.
– A group of stars that are gravitationally bound to each other is called a cluster.
• In an open cluster, the stars are not densely packed.
• In a globular cluster, stars are densely packed into a spherical shape.
– All stars, including the Sun, have nearly identical compositions—about 73 percent of a star’s mass is hydrogen, about 25 percent is helium, and the remaining 2 percent is composed of all the other elements.
B5 star
F5 star
K5 star
M5 star
– The differences in the appearance of their spectra are almost entirely a result of temperature effects.
– The main sequence, which runs diagonally from the upper-left corner to the lower-right corner of an H-R diagram, represents about 90 percent of stars.
– Red giants are large, cool, luminous stars plotted at the upper-right corner.
– White dwarfs are small, dim, hot stars plotted in the lower-left corner.
2. How can astronomers measure the speed at which a star is moving?
Spectral lines are shifted in wavelength by motion between the source of light and the observer. If a star is moving toward the observer, spectral lines are blueshifted. If a star is moving away, spectral lines are redshifted. The higher the speed, the larger the shift.
The Sun’s Life Cycle– The energy produced in the thin hydrogen layer forces
the outer layers of the star to expand and cool and the star becomes a red giant.
Stellar Evolution
– While the star is a red giant, it loses gas from its outer layers while its core becomes hot enough, at 100 million K, for helium to react and form carbon.
– When the helium in the core is all used up, the star is left with a core made of carbon.
– A white dwarf is stable because it is supported by the resistance of electrons being squeezed close together and does not require a source of heat to be maintained.
– A star that has less mass than that of the Sun has a similar life cycle, except that helium may never form carbon in the core, and the star ends as a white dwarf made of helium.
– A star that begins with a mass between about 8 and 20 times the Sun’s mass will end up with a core that is too massive to be supported by electron pressure.
– Once no further energy-producing reactions can occur, the core of the star violently collapses in on itself and protons and electrons in the core merge to form neutrons.
– A neutron star results from the resistance of neutrons to being squeezed, which creates a pressure that halts the collapse of the core.
– A neutron star has a mass of 1.5 to 3 times the Sun’s mass but a radius of only about 10 km.
– Infalling gas rebounds when it strikes the hard surface of the neutron star and explodes outward.
– A supernova (pl. supernovae) is a massive explosion in which the entire outer portion of the star is blown off and elements that are heavier than iron are created.
– A star that begins with more than about 20 times the Sun’s mass will not be able to form a neutron star.
– The resistance of neutrons to being squeezed is not great enough to stop the collapse, so the core of the star simply continues to collapse forever, compacting matter into a smaller and smaller volume.
– A black hole is a small, extremely dense remnant of a star whose gravity is so immense that not even light can escape its gravity field.
2. How is a neutron star different from a white dwarf?
Stellar Evolution
A white dwarf is created when the resistance of electrons to being squeezed stops the inward collapse of a star’s core. A neutron star is created when the original star does not lose enough mass to become a white dwarf. The pressure of the collapsing core causes protons and electrons to merge to form neutrons. The resistance of neutrons to be being squeezed halts the collapse of the core forming the neutron star.
Section 30.1 Main Ideas• The Sun contains most of the mass in the solar system
and is made up primarily of hydrogen and helium.
• Astronomers learn about conditions inside the Sun by a combination of observation and theoretical models.
• The Sun’s atmosphere consists of the photosphere, the chromosphere, and the corona.
• The Sun has a 22-year activity cycle caused by reversals in its magnetic field polarities.
• Sunspots, solar flares, and prominences are active features of the Sun.
• The solar interior consists of the core, where fusion of hydrogen into helium occurs, and the radiative and convective zones.
Section 30.1 Study Guide
Section 30.2 Main Ideas• Positional measurements of the stars are important for
measuring distances through stellar parallax shifts.
• Stellar brightnesses are expressed in the systems of apparent and absolute magnitude.
• Stars are classified according to the appearance of their spectra, which indicate the surface temperatures of stars.
• The H-R diagram relates the basic properties of stars: class, mass, temperature, and luminosity.
Section 30.2 Study Guide
Section 30.3 Main Ideas• The mass of a star determines its internal structure and
its other properties.
• Gravity and pressure balance each other in a star.
• If the temperature in the core of a star becomes high enough, elements heavier than hydrogen but lighter than iron can fuse together.
• Stars such as the Sun end up as white dwarfs. Stars up to about 8 times the Sun’s mass also form white dwarfs after losing mass. Stars with masses between 8 and 20 times the Sun’s mass end as neutron stars, and more massive stars end as black holes.
• A supernova occurs when the outer layers of the star bounce off the neutron star core, and explode outward.
Section 30.3 Study Guide
1. Which atmospheric layer of the Sun is visible under normal conditions?
a. photosphere c. convective zone
b. corona d. chromosphere
Multiple Choice
Chapter Assessment
The photosphere is the lowest layer of the Sun’s atmosphere. The chromosphere and corona are the upper two layers of the sun’s atmosphere which are usually only visible during a solar eclipse.
2. The apparent shift in the position of an object caused by the motion of the observer is called ____.
a. luminosity c. parallax
b. magnitude d. a parsec
The distance to a star can be estimated from its parallax shift. In this case, the motion of the observer is the change in position as the Earth orbits the Sun. Using the parallax technique, astronomers can find accurate distances up to 500 pc.
Multiple Choice
Chapter Assessment
Multiple Choice
3. What is the first fusion reaction in all stars?
a. helium to oxygen c. hydrogen to helium
b. silicon to iron d. oxygen to carbon
Chapter Assessment
Hydrogen to helium is the first fusion reaction in all stars. In the next reaction, when the core consists primarily of helium, it is fused to form oxygen. Stars will continue to generate sequentially heavier elements, though usually no heavier than iron, as its mass allows.
Multiple Choice
4. What causes sun spots?
a. prominence
b. magnetic irregularities
c. solar flares
d. solar wind
Chapter Assessment
Sun spots are caused by magnetic irregularities in the photosphere. Prominence, solar flares, and solar wind are all associated with sun spots.
Multiple Choice
5. Which of the following star classifications represents the highest temperature?
a. G c. F
b. K d. B
Chapter Assessment
Stars are assigned spectral types in the following order from hottest to coolest: O, B, A, F, G, K, and M. Each class is subdivided into more specific divisions with number from 0 to 9. The Sun is a type G2 star.
Short Answer
6. What happens halfway through the solar activity cycle?
Chapter Assessment
Halfway through the 22-year solar activity cycle, the Sun’s magnetic field reverses so that the north magnetic pole becomes the south magnetic pole.
Short Answer
7. What is a binary star? How common are they?
Chapter Assessment
A binary star is when two stars are gravitationally bound together and orbit a common center of mass. More than half of the stars in the sky are either binary stars or members of multi-star systems.
True or False
8. Identify whether the following statements are true or false.
______ The Sun has roughly the same density as Jupiter.
______ A parsec is roughly one-third of a light year.
______ About 90 percent of all stars are main sequence stars.
______ The Sun will someday become a white dwarf
made of helium.
______ A neutron star has a radius of only about 10 km.
Chapter Assessment
true
false
true
false
true
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