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Ch. 28 Sec. 1

Ch. 28 Sec. 1. Formation of the Solar System. Section 28.1. Formation of the Solar System. The solar system formed from the collapse of an interstellar cloud. Review Vocabulary. focus: one of two fixed points used to define an ellipse. I. Formation Theory. NASA Cassini.

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Ch. 28 Sec. 1

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  1. Ch. 28 Sec. 1 Formation of the Solar System

  2. Section 28.1 Formation of the Solar System The solar system formed from the collapse of an interstellar cloud. Review Vocabulary focus: one of two fixed points used to define an ellipse

  3. I. Formation Theory NASA Cassini • Direct observation & data from probes • Explanation of observations • 1. Shape of the solar system • 2. Differences among the planets • 3. Nature of asteroids, meteorites, and comets

  4. II. Collapsing Interstellar Cloud • Nebula • 1. Exist in space between the stars • 2. Hydrogen and helium gas • 3. Small amounts of other elements and dust

  5. B B. Radiate & reflect light 1. Dust blocks light (dark) 2. Starlight illuminates dust 3. Stars heat cloud (glow) Eagle Nebula Eagle Nebula

  6. C. Density of interstellar gas is low 1. Gravity slowly draws matter together 2. Pressure balances gravity

  7. D. Collapse • Begins slowly • Gradually accelerates • Cloud becomes much denser at its center • If rotating, the cloud spins faster as it contracts, due to centripetal force

  8. E. Collapse accelerates As a collapsing interstellar cloud spins, the rotation slows the collapse in the equatorial plane, and the cloud becomes flattened. Eventually, the cloud becomes a rotating disk with a dense concentration of matter at the center.

  9. The interstellar cloud that formed our solar system collapsed into a rotating disk of dust and gas. When concentrated matter in the center acquired enough mass, the Sun formed in the center and the remaining matter gradually condensed, forming the planets.

  10. F. Matter condenses • Temperature varied greatly with location • a. Inner planet – rocky • b. Outer planets – gas & ice

  11. III. Planetesimals & Planets • Nebula begins to collapse • Rotation begins • Dust combines to form planetesimals • More dust collects • Collision of planetesimals forms planets

  12. A. Gas giants form • Jupiter • a. Merging of icy planetesimals that contained mostly lighter elements • b. Gravity attracted additional gas & plantesimals • c. Disk in equatorial plane formed rings and satellites • 2. Saturn and the other gas giants formed similarly

  13. B. Terrestrial planet formation • Composed primarily of elements that resist vaporization • No satellite formation

  14. C. Debris • Icy objects known as comets • Rocky planetesimals known as asteroids

  15. Section 28.1 IV. Modeling the Solar System • Geocentric theory : Earth-centered • 1. Earth spins on its axis • 2. Explains appearance of celestial motions • a. Sunrise in east, etc. • 3. Could not readily explain retrograde motion

  16. The apparent backward movement of a planet is called retrograde motion. The changing angles of view from Earth create the apparent retrograde motion of Mars. Fig. 28.4 page 799

  17. B. Heliocentric model • Nicolaus Copernicus – 1543 • Explained retrograde rotation • Inner planets move faster than outer planets due to gravity

  18. Which observation provided evidence for the heliocentric model of the solar system? a. the nightly motion of the stars b.the rising and setting of the Sun c.the retrograde motion of planets d.the occurrence of meteor showers

  19. C. Kepler’s first law of Planetary Motion 1. From 1576–1601, before the telescope was used in astronomy, Tycho Brahe, a Danish astronomer, made accurate observations to within a half arc minute of the planets’ positions.

  20. 2. Kepler used Brahe’s observations 3. First Law – planet’s orbit is an ellipse a. Foci b. Major axis (semimajor axis) c. Astronomical unit (AU) – average distance from Earth to Sun

  21. Each planet has its own elliptical orbit, but the Sun is always at one focus. For each planet, the average distance between the Sun and the planet is its semimajor axis.

  22. 4. Earth’s semimajor axis is a unit used to measure distances within the solar system. Earth’s average distance from the Sun is 1.496 × 108 km, or 1 astronomical unit (AU).

  23. 5. The shape of a planet’s elliptical orbit is defined by eccentricity, which is the ratio of the distance between the foci to the length of the major axis.

  24. D. Kepler’s second law states that planets move faster when close to the Sun and slower when farther away. This means that a planet sweeps out equal areas in equal amounts of time.

  25. E. In Kepler’s third law, he determined the mathematical relationship between the size of a planet’s ellipse and its orbital period. This relationship is written as follows: P2= a3 P is time measured in Earth years, and a is length of the semimajor axis measured in astronomical units.

  26. F. Galileo • Used telescope a. Discovered 4 of Jupiter’s moons b. Lunar mountains & craters c. Sunspots d. Phases of Venus 2. Favored sun-centered theory

  27. The English scientist Isaac Newton described falling as a downward acceleration produced by gravity, an attractive force between two objects. He determined that both the masses of and the distance between two bodies determined the force between them.

  28. Newton’s law of universal gravitation is stated mathematically as follows: F is the force measured in newtons, G is the universal gravitation constant (6.6726 × 10–11 m3/ kg•s2), m1 and m2 are the masses of the bodies in kilograms, and r is the distance between the two bodies in meters.

  29. Which scientist first observed the moons of Jupiter with a telescope? a. Nicolaus Copernicus b.Tycho Brahe c.Isaac Newton d.Galileo Galilei

  30. V. Gravity A. Gravity and orbits Newton observed the Moon’s motion and realized that its direction changes because of the gravitational attraction of Earth. In a sense, the Moon is constantly falling toward Earth.

  31. B. Center of mass Newton determined that each planet orbits a point between it and the Sun called the center of mass. Just as the balance point on a seesaw is closer to the heavier box, the center of mass between two orbiting bodies is closer to the more massive body. Fig. 28.9 page 803

  32. VI. Present-Day Viewpoints Recent discoveries have led many astronomers to rethink traditional views of the solar system. Some already define it in terms of three zones: Zone 1, Mercury, Venus, Earth, and Mars; Zone 2, Jupiter, Saturn, Uranus, and Neptune; andZone 3, everything else, including Pluto.

  33. Examine the illustration. What relationship exists between the areas of the segments of the planet’s orbit?

  34. Answer: Kepler’s second law states that a planet sweeps out equal amounts of area in equal amounts of time. Therefore, each segment of the planet’s orbital ellipse has the same area.

  35. The solar system formed from the collapse of an interstellar cloud. • A collapsed interstellar cloud formed the Sun and planets from a rotating disk. • The inner planets formed closer to the Sun than the outer planets, leaving debris to produce asteroids and comets.

  36. Copernicus created the heliocentric model and Kepler defined its shape and mechanics. • Newton explained the forces governing the solar system bodies and provided proof for Kepler’s laws. • Present-day astronomers divide the solar system into three zones.

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