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Ch 28-31

Ch 28-31. Earth’s Role as a Body in Space. Lesson 1. Earth’s Position and Movement Through Space (You Are Here ). Earth’s Position in Space. What is Earth’s position within the hierarchy of the universe?. A. Earth’s Position in the Universe. Earth’s Position in the Universe… Earth 

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Ch 28-31

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  1. Ch 28-31 Earth’s Role as a Body in Space

  2. Lesson 1 Earth’s Position and Movement Through Space (You Are Here )

  3. Earth’s Position in Space What is Earth’s position within the hierarchy of the universe?

  4. A. Earth’s Position in the Universe Earth’s Position in the Universe… • Earth  • Solar System (3rd planet from Sun)  • Milky Way Galaxy (the Orion Arm)  • Local Group (about 40 galaxies) • Supercluster • Universe! http://www.atlasoftheuniverse.com/

  5. Earth’s Motion through Space How is Earth’s motion related to the origin of the galaxy and its solar system?

  6. The Origin of Our Expanding Universe 1. The Big Bang Theory • the universe began as a point and has been expanding ever since Notice how the galaxies in each successive picture are moving apart from the singularity? en.wikipedia.org

  7. The Origin of the Milky Way 2. Astronomers hypothesize that the galaxy began as… A rotating, spherical cloud in space … a. Our solar system continues to orbit the center of the Milky Way because… it developed in the plane of the disk around the central nuclear bulge http://www.google.com/imgres?imgurl=http://casswww.ucsd.edu/archive/public/tutorial/images/mw.jpg&imgrefurl=http://casswww.ucsd.edu/archive/public/tutorial/MW.html&usg=__

  8. The Milky Way • http://www.atlasoftheuniverse.com/

  9. The Milky Way • http://www.astropix.com/HTML/D_SUM_S/MILKYWAY.HTM

  10. b. A Diagram – Milky Way Galaxy Formation • http://lcogt.net/education/article/milky-way-galaxy • http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT423/HTML/AT42304.htm

  11. The Origin of the Solar System 3. Our solar system began when… …a rotating, interstellar cloud of gases (nebula) collapsed b/c of gravity to form a central protosun and orbiting planets a. Earth orbits the Sun because … it was located outside the center of the spinning nebula

  12. The Eagle Nebula • A solar nebula is… • A disk of dust and gas that can form a star and planets http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-astro-nebula.html

  13. A Diagram - Origin of the Solar System • http://csep10.phys.utk.edu/astr161/lect/solarsys/nebular.html

  14. Star formation has NEVER been observed! (just hypothesized!)

  15. Lesson 2 Kepler’s Laws and Earth’s Orbit

  16. Think About It… How would Earth be different if its orbit was more oval than circular?

  17. Focus Question How do Kepler’s laws describe Earth’s orbit?

  18. Kepler’s Laws (Introduction)… Johannes Kepler, working with data painstakingly collected by Tycho Brahe (from 1576-1601) without the aid of a telescope, developed three laws which described the motion of the planets across the sky. http://www.nmspacemuseum.org/halloffame/images.php?image_id=131 Unless otherwise noted, the info on the slides on Kepler’s laws was taken from the following website: http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html

  19. 1. Kepler’s First Law… The Law of Orbits: All planets move in elliptical orbits, with the sun at one focus. a. An ellipse is … an oval shape centered on two points instead of a single point. b. The orbital period of a planet is … the length of time it takes for it to travel a complete orbit around the sun. c. We call this a year!

  20. Examples of Ellipse Eccentricity Planetary orbit eccentricities

  21. 2. Kepler’s Second Law… The Law of Areas: A line that connects a planet to the sun sweeps out equal areas in equal times. • When the planet is closer to the sun, it moves faster, sweeping through a longer path in a given time. (to conserve angular momentum) • So a planet is moving fastest when it is closest to the Sun. http://www.mathacademy.com/pr/prime/articles/kepler/index.asp

  22. 3. Kepler’s Third Law… The Law of Periods: The square of the orbital period of any planet is proportional to the cube of the semimajor axis of its orbit. a. P² = a³(P = orbital period = unit of time in Earth yrs, a = length of the semimajor axis) • If you know the distance of a planet to the Sun, you would be able to figure out its… orbital period. • Basically… The closer a planet is to the Sun, the shorter its orbital period is.

  23. Kepler’s Third Law • Another way of thinking about this is that …The closer a planet’s orbit is to the Sun, the shorter its year will be. • For Examples: Appendix J on p. 921… • Mercury’s year is 88 (Earth) days • Venus’ year is 224 (Earth) days • Earth’s year is 365 (Earth) days • Mars’ year is 686 (Earth) days • Neptune’s year is 60,189 (Earth) days!!

  24. Kepler’s Laws Short Video http://www.youtube.com/watch?v=dRT3m2Wzyh4

  25. Practice! Orbit Eccentricity • The eccentricity of an ellipse can be defined as the ratio of the distance between the foci to the major axis of the ellipse. • The more eccentric an orbit, the more of an oval it is. • The eccentricity is zero for a circle. • Of the planetary orbits, only Pluto has a large eccentricity. http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=175

  26. Mini-Lesson 2: Barycenter The True Center of the Solar System!

  27. Mini Lesson 2: Barycenter and Earth’s Orbit… Barycenter is …the center of mass between a planet and the Sun. 1. The law of universal gravitation states that… • every pair of bodies in the universe attracts each other with a force related to… • …mass (the more mass they have, the stronger the pull) AND • …distance (the farther apart they are, the weaker the pull)

  28. Barycenter, Universal Gravitation, and the Wobbling Sun • The Sun wobbles around in its orbit because… • … the 8 planets are pulling on it as they orbit it!

  29. Barycenter and Earth’s Orbit… 2. A planet, such as Earth, actually orbits… its barycenter with the Sun 3. The Sun orbits … the barycenter of the solar system. (It is NOT stationary in the sky as planets orbit it.) 4. Draw this! See next slide. http://www.barewalls.com/pv-605547_Barycenter-Diagram.html

  30. Modeling Barycenter • http://spaceplace.nasa.gov/barycenter/

  31. Lesson 3 Earth’s Rotation Day and Night Earth’s Slightly Squashed Shape

  32. Think About It… How would Earth’s day be different if it did not rotate on its axis?

  33. Focus Questions… What causes the day and night cycle? What motion and force causes Earth’s slightly squished shape?

  34. Earth’s Rotation Causes Day and Night 1. Earth’s axis is… • … the imaginary line that goes through the N and S poles. 2. Day and night are caused by… • … the rotation of Earth on its axis - spinning towards and away from the Sun. (23.9345 hrs) 3. When the Sun “rises” … • … we are actually spinning TOWARDS it 4. When the Sun “sets” … • … we are actually spinning AWAY FROM it

  35. Think About It… Why are there 24 hours in a day? Earth spins… 15 degrees each hour There are 360 degrees in a circle (the circumference of Earth). 360 divided by 15 is 24 so there are 24 hours in a day! http://huntingtonastro.wikispaces.com/file/view/earth-rotation.png/199559520/earth-rotation.png

  36. Still Thinking About It… The exact amount of time it takes Earth to spin one time on its axis is… • 23.9345 hours (Write this in the margin!) If an Earth day was 5832.5 hours long (like that of Venus!) then… • It would take 243 days for Earth to spin one time on its axis! • Our day and night would be much longer! (And it would get really hot and really cold!)

  37. 1. What motion causes Earth to take the shape of an oblate spheroid? Earth’s rotation 2. What force causes the Earth’s mass to move outward from its center at the equator as Earth rotates? centrifugal force Earth’s Rotation Causes Its Slightly-squished Shape…

  38. Earth’s Rotation and Its Shape… http://www.cleonis.nl/physics/phys256/equatorial_bulge.php

  39. Earth’s Rotation Causes Its Slightly-squished Shape… 3. There is a slight bulging at the equator and a slight squishing at the poles. 4. This causes the circumference at the equator to be slightly larger than that of the poles.

  40. Earth’s Rotation and Its Shape… 5. Draw this  Notice the equatorial diameter is 42 km more than the polar diameter! Simulation: http://www.cleonis.nl/physics/phys256/equatorial_bulge.php

  41. Lesson 4 The Seasons

  42. Think About It… During which month is Earth closest to the Sun?

  43. Focus Question (and Answer!)… What causes the seasons? The tilt of the Earth on its axis as it revolves around (orbits) the Sun.

  44. Earth’s Orbit and Seasons… 1. The ecliptic is… • …the plane on which Earth orbits around the Sun http://en.wikipedia.org/wiki/Ecliptic

  45. Earth’s Orbit and Seasons… 2. The tilt of Earth’s axis relative to the ecliptic is 23.5 degrees. http://republicanredefined.com/2010/03/02/chile-quake-shifted-earths-axis-and-made-days-shorter/

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