The UniverseSection 1 Key Ideas 〉 How are stars formed? 〉 How can we learn about stars if they...
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Transcript of The UniverseSection 1 Key Ideas 〉 How are stars formed? 〉 How can we learn about stars if they...
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The Universe Section 1
Key Ideas
〉How are stars formed?
〉How can we learn about stars if they are so far away?
〉What natural cycles do stars go through?
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The Universe Section 1
What Are Stars?
〉How are stars formed?
〉Stars are formed from clouds of dust and gas, or nebulas, and go through different stages as they age.
• star: a large celestial body that is composed of gas and emits light
• light-year: the distance that light travels in one year; about 9.46 trillion kilometers
https://www.youtube.com/watch?
v=PM9CQDlQI0A
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The Universe Section 1
What Are Stars? continued
• Stars are powered by nuclear fusion reactions.
– The core of a star is extremely hot, extremely dense, and under extreme pressure.
– Nuclear fusion takes place in the core of a star.– Fusion combines the nuclei of hydrogen atoms into
helium.– When two particles fuse, energy is released.
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The Universe Section 1
Visual Concept: Nuclear Fusion
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The Universe Section 1
What Are Stars? continued
• Energy moves slowly through the layers of a star.
– Energy moves through the layers of a star by convection and radiation.
– During convection, hot gas moves upward, away from the star’s center, and cooler gas sinks toward the center.
– During radiation, atoms absorb energy and transfer it to other atoms in random directions. Atoms near the star’s surface radiate energy into space.
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The Universe Section 1
Structure of the Sun
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The Universe Section 1
Visual Concept: Structure of the Sun
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The Universe Section 1
Studying Stars〉How can we learn about stars if they are so far away?
〉The telescope allowed astronomers to study stars in more detail for the first time.
• Some stars appear brighter than others.– The brightness of a star depends on the star’s
temperature, size, and distance from Earth.– The brightest star in the night sky, Sirius, appears so
bright because it is relatively close to Earth.
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The Universe Section 1
Studying Stars, continued
• We learn about stars by studying energy.
– Stars produce a full range of electromagnetic radiation, from high-energy X-rays to low-energy radio waves.
– Scientists use optical telescopes to study visible light and radio telescopes to study radio waves emitted from astronomical objects.
– Earth’s atmosphere blocks some wavelengths, so telescopes in space can study a wider range of the spectrum.
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The Universe Section 1
Studying Stars, continued
• A star’s color is related to its temperature.
– Hotter objects glow with light that has shorter wavelengths (closer to the blue end of the spectrum).
– Cooler objects glow with light that has longer wavelengths (closer to the red end of the spectrum).
– Hot stars emit more energy at every wavelength than cooler stars do.
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The Universe Section 1
Starlight Intensity Graph
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The Universe Section 1
Studying Stars, continued
• Spectral lines reveal the composition of stars.
– The spectra of most stars have dark lines caused by gases in the outer layers that absorb light at that wavelength.
– Each element produces a unique pattern of spectral lines.
– Astronomers can match the dark lines in starlight to the known lines of elements found on Earth.
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The Universe Section 1
Visual Concept: Constellation
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The Universe Section 1
The Life Cycle of Stars〉What natural cycles do stars go through?
〉 In a way that is similar to other natural cycles, stars are born, go through various stages of development, and eventually die.
• The sun formed from a cloud of gas and dust.– The sun formed about 5 billion years ago.– The sun was “born” when the process of fusion began
in the core.
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The Universe Section 1
The Life Cycle of Stars, continued
• The sun has a balance of inward and outward forces.– The fusion reactions in the core of the sun produce an
outward force that balances the inward force due to gravity.
– Over time, the percentage of the sun’s core that is helium becomes larger.
– Scientists estimate that the sun can continue nuclear fusion for another 5 billion years.
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The Universe Section 1
• The sun will become a red giant before it dies.– As fusion slows, the outer layers of the sun will expand.– The sun will become a red giant.
• red giant: a large, reddish star late in its life cycle
– When the sun runs out of helium, the outer layers will expand and eventually leave the sun’s orbit.
– The sun will become a white dwarf.
• white dwarf: a small, hot dim star that is the leftover center of an old star
The Life Cycle of Stars, continued
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The Universe Section 1
• Supergiant stars explode in supernovas.– Massive stars evolve faster, develop hotter cores, and
create heavier elements through fusion.– The formation of an iron core signals the beginning of
a supergiant’s death.– Eventually the core collapses and then explodes in a
supernova.
• supernova: a gigantic explosion in which a massive star collapses and throws its outer layers into space, plural supernovae
The Life Cycle of Stars, continued
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The Universe Section 1
• Some supernovas form neutron stars and black holes.– If the core that remains after a supernova has a mass
of 1.4 to 3 solar masses, the remnant can become a neutron star.
– If the leftover core has a mass that is greater than three solar masses, it will collapse to form a black hole.
• black hole: an object so massive and dense that not even light can escape its gravity
The Life Cycle of Stars, continued
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The Universe Section 1
• The H-R diagram shows how stars evolve.– The vertical line on an H-R diagram indicates
brightness in absolute magnitude.– The horizontal line on the H-R diagram indicates
temperature.– Most stars appear in a diagonal line called the main
sequence.– As stars age and pass through different stages, their
positions on the H-R diagram change.
• The sun is currently a main-sequence star.
The Life Cycle of Stars, continued
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The Universe Section 1
H-R Diagram
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The Universe Section 1
Visual Concept: Types of Stars
https://www.youtube.com/watch?
v=FCH2s-4b1mM