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Explore the Sun’s size, heat, and layers, and learn how it generates energy through fusion. Discover the features of the Sun, including sunspots, solar winds, and auroras, and understand planetary movement and retrograde motion. Delve into the history of observing the Solar System and the geocentric model.
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Chapter 26 The Sun & The Solar System
Chapter 26.1 The Sun’s Size, Heat, and Structure
The Sun’s Size • Diameter of about 1,400,000 kilometers • Could fit around 1 million Earths inside the Sun • Not a large star compared to other stars
The Sun’s Energy • All stars get their energy from fusion • Fusion = the combining of the nuclei of lighter elements to form heavier elements • E=mc2 (energy is equal to mass times the speed of light squared) • Means that matter can be converted into energy, which happens during fusion
The Sun’s Energy • Stars have such intense heat and pressure that atoms are torn apart into nuclei and electrons • Hydrogen and Helium exist as plasma • Plasma = a fourth state of matter consisting of charged particles
The Sun’s Energy • The nuclei are moving at such great speeds and under intense heat that they will fuse • When the nuclei fuse, it creates energy
Describe in your own words how the Sun generates so much energy.
The Sun’s Layers • The Core • Consists mostly of hydrogen and helium ions in a plasma state • 100 times as dense as water • Temperature : 15,600,000 oC
The Sun’s Layers • Radiative Zone • Layer of plasma that lies around the core • Temperature: cooler than the core • 8,000,000 oC near the core • 2,000,000 oC near the convection zone
The Sun’s Layers 3. Convection Zone • Rising and falling currents of plasma carry energy to the sun’s surface, where it is radiated out into space as sunlight • Temperature: 1,500,000 oC
The Sun’s Layers 4. Photosphere • The visible surface of the sun • Tops of the currents form structures called granules • 1,000 km wide and last for 20 minutes • Temperature: 6,000 oC
The Sun’s Layers 5. Chromosphere • Inner layer of the Sun’s atmosphere • Extends thousands of kilometers above the photosphere • Temperature : 20,000 oC • Hydrogen within emits a distinctive reddish light • Solar prominences: dense clouds of material that can erupt and extend into space
The Sun’s Layers 6. Corona • Thin outer atmosphere • Million times less bright than the photosphere • Temperature: 1,000,000 oC to 3,000,000 oC
Sunspots • Dark spots on the photosphere • Range in size from barely visible to four time larger than Earth’s diameter • Very hot and bright • Look dark because the surrounding photosphere is so much hotter and brighter • Magnetic field is 1,000 times stronger than the surrounding photosphere
Sunspot Movement • Move from left to right across the sun’s surface • Indicates that the sun rotates on an axis • The sun is not a solid so the rate of rotation varies from place to place • Equator = 25 days • Poles = 34 days • 11 year cycle of peak activity
Solar Winds • Produced by a constant stream of electrically charged particles given off by the corona • Travel through space at speeds of about 450 km per second • Earth’s magnetic field deflects most solar winds
Auroras • As solar wind blows by past Earth, some particles interact with Earth’s magnetic field and upper atmosphere • Causes displays of color and light in the upper atmosphere • Called northern lights because they occur in regions near Earth’s magnetic poles
Mars has either no magnetic field or a very weak one. Why does this fact make it unlikely that life exists at the present time on the surface of mars?
Observing the Solar System: A History Chapter 26.2
The Movement of Planets and Stars • For thousands of years people believed that Earth stood still in the center of the universe • Geocentric Model = Earth – Centered Model
Star Movement? • As long as 6,000 years ago, astronomers were recording the movement of the stars • Imagined that stars were like holes in a solid celestial sphere that surrounded the Earth
Star Movement? • Beyond the sphere, was an intense light that shone through the holes • Concluded that the stars moved around Earth as the sphere rotated
Draw a picture of a geocentric model with the celestial sphere of stars
Constellations • Early astronomers noticed that the same constellation, or groups of stars, became visible at the same time every year. • Many cultures used the changing of constellations as a basis for a calendar
Planetary Movement • Early astronomers noted that not all points of light in the sky are fixed in constellations • Some wander across the sky, changing position over the course of days, weeks, and months • Inferred that these points of light were other planets that are closer to Earth than the stars are
Retrograde Motion • Early astronomers observed that most of the time planets moved eastward relative to the background of constellations EAST WEST
Retrograde Motion • Periodically the planets stopped moving eastward and moved westward for a few weeks, then resumed their eastward paths • This pattern of backward motions is called Retrograde Motion
What is retrograde motion? What do you think is causing this phenomenon?
Ptolemy’s Geocentric Model • Greek astronomer who lived in Egypt in 200 A.D • Developed a model that could be used to predict the location of the planets • Ptolemy’s model was used by astronomers until the 16th century
Ptolemy’s Geocentric Model • Each planet moves on small circular orbits called epicycles • The center of each small orbit moved around Earth on a larger circular orbit called a deferent
Ptolemy’s Geocentric Model • Retrograde motion occurred when the planet moved along the part of the epicycle that an observer on Earth could see. • However, Ptolemy’s model didn’t work perfectly. Observations did not always correlate with the models predictions
How did Ptolemy account for retrograde motion in his model of the solar system?
Copernicus’s Heliocentric Model • Polish Astronomer - 1473-1543 • Proposed a Heliocentric Model: Sun – centered solar system • Suggested that Earth was a rotating planet that revolved around the Sun
Copernicus’s Heliocentric Model • Retrograde Motion is a result of planets orbiting the Sun counterclockwise at different distances and speeds • Example: • Earth orbits faster than Mars • When Earth overtakes and begins to pass Mars, it make Mars appear to move backward • After Earth has fully passed, Mars’s normal motion appears to resume
Retrograde Motion Video • http://www.youtube.com/watch?v=72FrZz_zJFU
Use a Venn diagram to compare and contrast Ptolemy’s Model and Copernicus’s Model?
Tycho, Kepler, & Planetary Motion Tycho Brahe: Danish astronomer in the 16th Century • Studied the movement of moons and planets throughout their entire orbit • Discovered unexpected occurrences within the orbits • His record were the most precise before the invention of the telescope
Kepler’s Laws • Johannes Kepler - Tycho’s assistant • Discovered that the unexpected occurrences could be explained if the planets’ orbits were elliptical, rather than round • Developed 3 Laws of Celestial Mechanics
1st Law of Planetary Motion • Planets travel in elliptical orbits with the sun at one focus • An ellipse has two foci on opposite side of the center • Since the Sun is located at one focus of the ellipse, a planet’s distance from the sun will change throughout its orbit
2nd Law of Planetary Motion • Equal Area Law: each planet moves around the sun in such a way that an imaginary line joining the planet to the sun sweeps over equal areas of space in equal periods of time • Means that the speed at which a planet travels around the sun is not constant • Planets travel faster when they are closer to the Sun
3rd Law of Planetary Motion • Harmonic Law: The period (P) of a planet squared is equal to the cube of its mean distance (D) from the Sun. P2 = D 3 • The farther the planet is from the sun, the longer its period of revolution
Isaac Newton and the Law of Gravitation • English scientist and mathematician 1642-1727 • Developed an explanation for what kept the planets in motion
Law of Gravitation • Every mass exerts a force of attraction on every other mass
Law of Gravitation • Every mass exerts a force of attraction on every other mass • The strength of that force is proportional to each of the masses
Law of Gravitation • Every mass exerts a force of attraction on every other mass • The strength of that force is proportional to each of the masses • The strength of that force is inversely proportional to the distance between them