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Unit 2 Lesson 3 The Sun
Copyright © Houghton Mifflin Harcourt Publishing Company
Here Comes the Sun
Copyright © Houghton Mifflin Harcourt Publishing Company
What do we know about the sun?
• The sun is a hot ball of gas composed mostly of the elements hydrogen and helium.
• The sun formed about 4.6 billion years ago.
• Of the light emitted from the sun, 41 percent is visible light, 9 percent is ultraviolet light, and 50 percent is infrared radiation.
• Without the sun, there would be no life on Earth.
Unit 2 Lesson 3 The Sun
What is the structure of the sun?
• The sun is a spherical body with a layered atmosphere and an interior composed of layers.
• Energy is produced in the core (or middle) of the sun and is transported to the surface through the radiative zone and the convective zone.
• The sun’s atmosphere has three layers: the photosphere, the chromosphere, and the corona.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
What is the structure of the sun?
• The sun’s surface is the photosphere. Energy escapes the sun from this layer.
• The middle layer of the sun’s atmosphere is the chromosphere, and its temperature rises with distance from the photosphere.
• The sun’s outer atmosphere is the corona, which extends millions of kilometers into space.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
What is the structure of the sun?
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
• What are the layers of the sun and its atmosphere?
Let’s Get Together
Copyright © Houghton Mifflin Harcourt Publishing Company
How does the sun produce energy?
• Matter can change into energy according to the equation E = mc², where E is energy, m is mass, and c is the speed of light.
• The sun generates energy through the process of nuclear fusion.
• Nuclear fusion is the process by which two or more low-mass atomic nuclei fuse to form another, heavier nucleus.
Unit 2 Lesson 3 The Sun
How does the sun produce energy?
• Nuclear fusion takes place in the core of stars.
• In stars with core temperatures similar to the sun’s, the fusion process starts with the fusion of two hydrogen nuclei.
• In older stars with hotter cores, helium fuses into carbon.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
How does the sun produce energy?
• In the sun’s core, hydrogen nuclei sometimes fuse to form a helium nucleus in a three-step process.
• In the first step, two protons collide to form a nucleus of deuterium, which has one proton and one neutron.
• Deuterium is a form of hydrogen.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
How does the sun produce energy?
• Next, a deuterium nucleus collides with another proton to form a variety of helium called helium-3.
• In the third step, two helium-3 nuclei collide and form a helium-4 nucleus that has two protons and two neutrons.
• Two protons are released.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
How does the sun produce energy?
• The entire chain of fusion reactions requires six hydrogen nuclei and results in one helium nucleus and two hydrogen nuclei.
• Approximately 1038 collisions between hydrogen nuclei take place in the sun’s core every second.
• These reactions keep the sun shining.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
Mixing It Up
Copyright © Houghton Mifflin Harcourt Publishing Company
How is energy transferred to the sun’s surface?• Energy is transferred to the sun’s surface by two
different processes.
• Energy is transferred from the sun’s core through the radiative zone by radiation.
• Energy is transferred from the top of the radiative zone through the convective zone to the photosphere by convection.
Unit 2 Lesson 3 The Sun
How is energy transferred to the sun’s surface?• Energy travels through the radiative zone in the
form of electromagnetic waves.
• The radiative zone is densely packed with particles such as hydrogen, helium, and free electrons.
• Electromagnetic waves are repeatedly absorbed and re-emitted by particles until they reach the top of the radiative zone.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
How is energy transferred to the sun’s surface?• In the convective zone, energy is transferred by
the movement of matter.
• Hot gases rise to the surface of the sun, cool, and then sink back into the convective zone.
• This process, called convection, takes place in convection cells, which form granules on the sun’s surface.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
How does the sun rotate?
• Because it is a giant ball of gas, the sun rotates faster at its equator than it does at higher latitudes.
• This kind of rotation is called differential rotation.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
How does the sun rotate?
• Near the equator, the sun rotates once in about 25 days, but at the poles it rotates once in about 35 days.
• The sun’s interior does not rotate in the same way as the surface.
• The sun’s core and radiative zones rotate together, at the same speed.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
How does the sun rotate?
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Unit 2 Lesson 3 The Sun
• At which point does the sun rotate fastest?
The Ring of Fire
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What is solar activity?
• Solar activity refers to variations in the appearance or energy output of the sun.
• Solar activity on the sun’s surface includes sunspots, solar flares, and prominences.
Unit 2 Lesson 3 The Sun
What is solar activity?
• Dark areas that form on the surface of the sun are called sunspots. They are about 1,500 °C cooler than the areas that surround them.
• Sunspots range in width from a few hundred kilometers to 10 to 15 times the diameter of Earth.
• Sunspot activity occurs on average in 11-year cycles, in which the activity increases and then decreases.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
What is solar activity?
• A solar flare is an explosive release of energy that can extend outward as far as the sun’s outer atmosphere.
• During a solar flare, the sun ejects large numbers of high-energy particles, along with radiation from across the entire electromagnetic spectrum.
• Temperatures within solar flares reach millions of degrees Celsius.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
What is solar activity?
• Huge loops of relatively cool gas that extend from the photosphere thousands of kilometers into the outer atmosphere are called prominences.
• Several objects the size of Earth could fit inside a loop of a prominence.
• Prominences generally last from several hours to a day, but some can last for several months.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
What is the structure of the sun?
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2 Lesson 3 The Sun
• Identify sunspots, solar flares, and prominences in this image of the sun.