Lesson 1-1 The electromagnetic spectrum is a continuous range of wavelengths. Looking at the Night...
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Transcript of Lesson 1-1 The electromagnetic spectrum is a continuous range of wavelengths. Looking at the Night...
![Page 1: Lesson 1-1 The electromagnetic spectrum is a continuous range of wavelengths. Looking at the Night Sky (cont.)](https://reader035.fdocuments.us/reader035/viewer/2022062519/5697bfa91a28abf838c9a263/html5/thumbnails/1.jpg)
The electromagnetic spectrum is a continuous range of wavelengths.
Looking at the Night Sky (cont.)
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Different parts of the electromagnetic spectrum have different wavelengths and different energies. You can see only a small part of the energy in these wavelengths.
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An astronomical unit is the average distance between Earth and the Sun, about 150 million km.
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• A light-year is the distance light travels in 1 year.
• One light-year is about 10 trillion km.
Measuring Distances (cont.)
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The apparent magnitude of an object is a measure of how bright it appears from Earth.
Measuring Brightness
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• Luminosity is the true brightness of an object.
• The luminosity of a star, measured on an absolute magnitude scale, depends on the star’s temperature and size, not its distance from Earth.
Measuring Brightness (cont.)
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• nuclear fusion
• star
• radiative zone
• convection zone
The Sun and Other Stars
• photosphere
• chromosphere
• corona
• Hertzsprung-Russell diagram
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How Stars Shine• A star is a large ball of gas held together
by gravity with a core so hot that nuclear fusion occurs.
• Nuclear fusion occurs when the nuclei of several atoms combine into one larger nucleus.
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How Stars Shine (cont.)
• Nuclear fusion releases a large amount of energy.
• A star shines because when energy leaves a star’s core, it travels throughout the star and radiates into space.
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Spectra of the Sun and other stars provide information about stellar composition.
Composition and Structure of Stars
stellar
Science Use anything related to stars
Common Use outstanding, exemplary
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• There are three interior layers of a typical star.
• When first formed, all stars fuse hydrogen into helium in their cores.
Composition and Structure of Stars (cont.)
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• The radiative zone is a shell of cooler hydrogen around a star’s core.
• In the convection zone, hot gases move toward the surface as cooler gases move down into the interior.
Composition and Structure of Stars (cont.)
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Beyond the convection zone are the three layers of a star’s atmosphere—the photosphere, the chromosphere, and the corona.
Composition and Structure of Stars (cont.)
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The photosphere is the apparent surface of a star, where light energy radiates into space.
Composition and Structure of Stars (cont.)
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• The chromosphere is the orange-red layer above the photosphere.
• The corona is the wide, outermost layer of a star’s atmosphere.
Composition and Structure of Stars (cont.)
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Changing Features of the Sun: Sunspots
• Cooler regions of magnetic activity
• Seem to move as the Sun rotates
• Number varies on an 11-year cycle
Digital Vision/PunchStock
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Changing Features of the Sun: Coronal Mass Ejections (CMEs)
• Huge gas bubbles ejected from the corona
• Larger than flares
• May reach Earth
• Can cause radio blackouts
NASA
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Changing Features of the Sun: Prominences and Flares• Prominences—
clouds and jets of gases forming loops into the corona
• Flares—sudden increases in brightness, often near sunspots or prominences
SOHO Consortium, ESA, NASA
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Changing Features of the Sun: The Solar Wind• Caused by
charged particles streaming away from the Sun
• Extends to the edge of the solar system
• Causes auroras CORBIS
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• Most stars exist in star systems bound by gravity.
• Many stars exist in large groupings called clusters.
• Stars in a cluster all formed at about the same time and are the same distance from Earth.
Groups of Stars
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• Scientists classify stars according to their spectra.
• Though there are exceptions, color in most stars is related to mass.
Classifying Stars
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Blue-white stars tend to have the most mass, followed by white stars, yellow stars, orange stars, and red stars.
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The Hertzsprung-Russell diagram is a graph that plots luminosity against temperature of stars.
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The y-axis of the H-R diagram displays increasing luminosity and the x-axis displays decreasing temperature.
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The mass of a main-sequence star determines both its temperature and its luminosity
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• nebula
• white dwarf
• supernova
• neutron star
• black hole
Evolution of Stars
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• Stars form deep inside clouds of gas and dust.
• A cloud of gas and dust is a nebula.
Life Cycle of a Star
nebula
from Latin nebula, means “mist” or “little cloud”
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Star-forming nebulae are cold, dense, and dark.
Life Cycle of a Star (cont.)
Photo courtesy of NASA/Corbis
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• Gravity causes the densest parts to collapse, forming regions called protostars.
• Over many thousands of years, the energy produced by protostars heats the gas and dust surrounding them.
Life Cycle of a Star (cont.)
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• A star becomes a main-sequence star as soon as it begins to fuse hydrogen into helium.
• Low-mass stars stay on the main sequence for billions of years, and high-mass stars are there for only a few million years.
Life Cycle of a Star (cont.)
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• When a star’s hydrogen supply is nearly gone, the star leaves the main sequence and begins the next stage of its life cycle.
• All stars form in the same way, but stars die in different ways, depending on their masses.
• Massive stars eventually become red supergiants.
Life Cycle of a Star (cont.)
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• After helium in the cores of lower-mass stars is gone, the stars cast off their gases exposing their cores.
• The core eventually becomes a white dwarf, a hot, dense, slowly cooling sphere of carbon.
• This is what is expected to happen to the Sun.
End of a Star
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The Sun will remain on the main sequence for 5 billion more years.
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When the Sun becomes a red giant for the second time, it will probably absorb Earth and push Mars and Jupiter outward.
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When the Sun becomes a white dwarf, the solar system will be a cold, dark place.
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• Very massive stars can explode in a supernova, which destroys the star.
• Iron in the core does not fuse and the core collapses quickly under the force of gravity.
• The normal space within atoms is eliminated, leaving a dense core of neutrons, or a neutron star.
End of a Star (cont.)
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• For the most massive stars, atomic forces holding neutrons together are not strong enough to overcome so much mass in such a small volume. Gravity is too strong, and the matter crushes into a black hole.
• A black hole is an object whose gravity is so great that no light can escape.
End of a Star (cont.)