Ch. 5 The Universe and Solar System

1. Ch. 5 The Universe and Solar System Pg 124-147

2. Origin and Structure of the Universe • The Universe Defined • The universe consists of all the matter, energy, and space that have existed since the beginning of time. • Most of the distance between stars is empty space. • Universe consists of empty space, stars, planets, satellites, asteroids, comets, & meteoroids. • Interstellar gas & dust, H & atomic particles.

3. Galaxies • Galaxies are clusters of stars and stars and galaxies aren’t evenly distributed in space. • 3 Types of Galaxies: • Spiral: shaped like a flat disk or pinwheel with a bright, bulging central core. • Elliptical: shaped like an ellipse or sphere. • Irregular: oddly shaped and resembles an explosion frozen in time.

4. Spiral Galaxies • Central core contains older stars. • Spiral arms radiate outward from center and wrap around the galaxy. • Arms contain numerous young stars and interstellar gas and dust. • Shape comes from their rotation.

5. Elliptical Galaxies • Contains older stars and lacks the interstellar gas and dust needed for new star development. • Most large galaxies are spiral galaxies but, elliptical galaxies seem to be more numerous.

6. Irregular Galaxies • Contain a large amount of interstellar gas and dust which indicates young star development. • Only a small percentage of all known galaxies are irregular galaxies.

7. The Milky Way Galaxy • 1780 Sir William Herschel was able to use observations and calculations to show that the Earth and the Sun are located in a disk shaped group of stars called a galaxy. • Our galaxy is the Milky Way galaxy and it is a spiral shaped galaxy. • We reside in an arm of our galaxy and the bright band in the sky is the galaxy itself.

8. Distances in Space • AU—astronomical unit: 150,000,000km; the distance between our planet and the sun. • Light year—LY: 41,000,000,000,000km or 41 trillion km. • A light year is the distance light travels in 1 year, about 9.46 trillion km. • The nearest star is 4.3 light years away.

9. Origin of the Universe: The Big Bang Theory • Scientists think that nearly 15 billion years ago the universe was created. • Think it was an explosive event which produced all the matter and energy in the universe. • We call it the Big Bang Theory and there’s a lot of evidence to support this but there still are unanswered questions and unknown details.

10. Big Bang Theory • Suggests that all matter and energy that exist today in the universe was concentrated in a very small dense object. • For some reason it began to expand, creating time and space. • Lighter elements formed, followed by heavier elements and stars began to evolve.

11. Big Bang Theory • Proof: 1929 Edwin Hubble observed that galaxies are moving away from each other—that the universe is expanding. • Red shift—means movement is away. • Proof 2: 1965 Arno Penzlas and Robert Wilson discovered background radiation—a remnant of the Big Bang. It is evenly distributed. • Proof 3: 1995 NASA discovered deuterium (heavy isotope of H) scattered throughout the universe.

12. Alternative Theory: The Oscillating Universe • Some scientists think the universe will not continue to expand indefinitely. • Expansion will be reversed by the gravitational attraction of all the matter in the universe. • This is the pulsating or oscillation universe theory. • Weak evidence in support of this theory.

13. Another Alternative Theory: The Steady State Universe • Steady State Universe Theory was proposed in the late 1940s. • Suggests that the universe is unchanging and never had a beginning and will never have an ending. • New matter is created to fill voids in space and to maintain a consistent density of galaxies. • Ruined in 1965—Background radiation as proof of the Big Bang Theory.

14. Classification of Stars • Stars vary in color due to the wavelength of light they give off. • Red light = cool stars. • Blue light = hot stars. • Stars vary in brightness, or magnitude. • Apparent magnitude is how bright a star appears to be when seen from the Earth. • Absolute magnitude is how bright the star really is.

15. Classification of Stars • Apparent magnitude is a function of the star’s absolute magnitude and its distance from the Earth. • Ex: faint star looks bright because it is close to the Earth. • Ex: brighter star looks faint because it is so much farther away from the Earth than the faint star in the 1st example.

16. Classification of Stars • EjnarHertzsprung and Henry Norris Russell recognized the relationship between the absolute magnitude and the temperature of stars by plotting the data from many stars on a graph. • This graph is the Hertzsprung-Russell Diagram or H-R Diagram. • It shows that stars fall into groups related to their temperature and brightness.

17. Classification of Stars • Main sequence: The majority of stars plot in this band, ranging from cool dim stars to hot bright stars. • Giants: above the main sequence is this cluster of bright cool stars. • Supergiants: Above the giants is this cluster of very bright cool stars. • White dwarfs: Below the main sequence is this group of hot dim stars.

18. Classification of Stars • The H-R Diagram suggests that all stars pass through a series of stages in their life cycles.

19. Classification of Stars • Life stages of a star: • Gas & dust particles come together & compact. • Increase in pressure & temperature by becoming more dense & compact. • Stars to emit radiation. • If star is hot enough, nuclear fusion takes place taking 4 H nuclei & releasing 1 He nucleus, 2 positrons, & energy. • Star is stable.

20. Classification of Stars • Life stages of a star: • As energy is depleted, nuclear fusion stops and the star collapses, generating lots of heat. • The heat causes the star to rapidly expand and becomes a red giant or supergiant star. • It collapses and explodes, losing its outer layers. • This flare up of a star is called a nova or supernova. • The dying star shrinks into a white dwarf and becomes dull and cold.

21. Classification of Stars • The length of a star’s life cycle depends on how much gas and dust was present in the initial cloud and on how massive the star became.

22. Our Sun: An Average Star • The Sun is a stable, average size yellow star in the main sequence. • Has a surface temperature of 5500°C. • Largest object in our solar system—a million Earths could fit inside it. • Light takes 8 minutes and 20 seconds to reach the Earth. • Much of what we know about the Sun has been learned by analyzing the light from it.

23. Our Sun: An Average Star • Like other stars, complex processes in the sun produce other elements. • H & He combine to form other heavier atoms. • Does this under high pressure and temperature. • More than 60 elements have been identified in the sun’s gases. • 75% of the sun’s mass is H, 24% is He, the rest is made up of other elements.

24. Earth and Our Solar System • Formation of the Solar System • Scientists think the expanding clouds of dust & gas from the Big Bang gradually condensed to form galaxies filled w/stars. • Our Sun began 5 billion years ago and accounts for 99% of all the matter in our solar system.

25. Earth’s Position in the Solar System • Ptolemy: 150 AD, Egyptian astronomer Ptolemy developed a Geocentric model of the solar system. • Copernicus: Early 1500s, Polish astronomer Nicolaus Copernicus proposed a Heliocentric model of the solar system. • It explained and predicted the motion of the planets better but, it wasn’t accepted at the time.

26. Earth’s Position in the Solar System • Brahe: Late 1500s, Danish astronomer Tycho Brahe built an observatory and made observations and calculations on the movement of the planets. • Kepler: 1600, German astronomer Johannes Kepler became Tycho’s assistant and used and studied Tycho’s records to describe planetary motion with mathematical laws.

27. Earth’s Position in the Solar System • Galileo: 1609, Italian astronomer Galileo Galilei built a telescope and was the 1st scientist to study the sky. • He discovered the 4 biggest moons of Jupiter & the phases of Venus. • He accepted Copernicus’s Heliocentric model of the solar system but, it wasn’t accepted at the time. (He was persecuted for this).

28. Gravity: A Universal Force • Every object in the universe exerts a gravitational pull on every other object. • Trend: The greater the masses, the greater the gravitational force and the farther apart the objects, the weaker the gravitational force. • Gravity is responsible for the spherical shape of large objects in the universe.

29. Placing a Satellite in Orbit • Orbit: is the path of a body revolving around another body. • For a satellite to orbit the Earth, the forces created by the satellite’s orbital speed and the Earth’s gravitational pull must be in balance. • Greater gravitational force of the Earth = satellite will fall to the Earth; greater orbital speed of the satellite = satellite will go into orbit higher above the Earth.

30. Kepler’s 3 Laws of Planetary Motion—Early 1600s • 1. The Law of Ellipses. The orbit of each planet is an ellipse. • 2. The Law of Areas. An imaginary line connecting a planet to the sun sweeps out equal areas in equal amounts of time. • 3. The Harmonic Law. p^2 = d^3; where p is the period of revolution in years and d is the distance from the sun in AUs. (pg 144-math).

31. Orbits within Our Solar System • All objects that revolve around the sun are influenced by the sun’s gravitational pull. • Orbits of planets, asteroids, comets, and etc. are elliptical. • Perihelion: is an object’s closest point to the sun. January for the Earth. • Aphelion: is an object’s farthest point from the sun. July for the Earth.

32. Orbits within Our Solar System • Most asteroids are located between the orbits of Mars and Jupiter and have orbits similar to the planets. • Asteroids have elongated orbits that take them from a position close to the sun to a position beyond Jupiter’s orbit. • The orbits of comets are the most elongated.