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For Wednesday, Feb. 12

For Wednesday, Feb. 12. Reading: Section 3.3 Assignments: Mini-Project #2 (due Wed. Feb. 12) Homework #2 (due Tue. Feb. 11 – 3 pm) QUIZ #1 FRIDAY FEB. 14 Planetarium shows this week (see Blackboard announcement) Telescope session Wednesday at 6 pm?. For Review Thought Questions:.

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For Wednesday, Feb. 12

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  1. For Wednesday, Feb. 12 Reading: Section 3.3 Assignments: Mini-Project #2 (due Wed. Feb. 12) Homework #2 (due Tue. Feb. 11 – 3 pm) QUIZ #1 FRIDAY FEB. 14 Planetarium shows this week (see Blackboard announcement) Telescope session Wednesday at 6 pm?

  2. For Review Thought Questions: ClassAction site: http://astro.unl.edu/classaction/

  3. Kepler 11 Planet System:

  4. How Does the Solar System Work? What clues can tell us how the planets actually move? Distances to planets and Sun helped settle whether Earth or Sun was at the center of everything… GEOCENTRIC MODEL HELIOCENTRIC MODEL

  5. Mission to Pluto

  6. Finding Planets • Jupiter • white; very bright • Saturn • yellow; medium bright • Mars • noticeably red • Venus • often brightest “star” when visible; only seen around sunrise or sunset • Mercury • difficult to see; always close to Sun in sky

  7. Planet Motions • OVER MANY NIGHTS:slowly move through constellations (usually W to E) • planets stay near ecliptic • (Sun’s path through zodiac constellations) DURING ONE NIGHT: move E to W across sky (due to Earth’s rotation) VIEW FROM EARTH W E E S W

  8. “Inferior Planets”: Mercury, Venus VENUS VENUS • always near Sun in sky • best seen just before sunrise or just after sunset • never seen at midnight MERCURY MERCURY LOOKING EAST AT SUNRISE LOOKING WEST AT SUNSET

  9. “Superior Planets”: Mars, Jupiter, Saturn • sometimes seen high overhead at midnight • usually move W to E relative to stars: “prograde motion” • sometimes move E to W relative to stars: “retrograde motion” Mars in prograde motion (compared to stars) E W Mars in retrograde motion

  10. Thought Question: Where would planet A be seen in the sky from Earth at sunset? A

  11. Thought Question: At roughly what time would the planet at position 5 be highest above the horizon? (Remember that Earth rotates counterclockwise from this point of view.) • 3 am • 9 am • 3 pm • 9 pm • It is not possible to tell from the diagram

  12. Thought Question: At roughly what time would planet A be seen highest above the horizon? (Remember that Earth rotates counterclockwise from this point of view.) • 3 am • 9 am • 3 pm • 9 pm • It is not possible to tell from the diagram A

  13. Retrograde Motion → happens when Earth catches and passes a superior planet

  14. Kepler’s Laws of Planetary Motion Discovered after years of trial and error… Kepler’s First Law: (SHAPES OF ORBITS) All planet orbits are ellipses with Sun at one focus eccentricity flashlet applet

  15. Ice Dwarfs Eris MAP OF PLUTO:

  16. Ice Dwarfs ERIS SEDNA PLUTO • orbits more elliptical than Pluto’s ERIS

  17. For Friday, Feb. 14 QUIZ #1 – BRING A CALCULATOR Assignments: Mini-Project #2 (due today) Planetarium shows this week (see Blackboard announcement) Telescope session Wednesday at 6 pm

  18. Comets Orbit

  19. Ellipses semi-major axis (A): half length of long side → average distance from Sun eccentricity (e): center Sun c A rP rA aphelion: farthest point from Sun perihelion: closest approach to Sun Sun A SPECIAL CASE: CIRCLE (e=0) semi-major axis (A) equals radius

  20. Thought Question: NASA wants to launch a spacecraft to go from Earth’s orbit to Mars’ (outer) orbit and immediately come back. Which of the pictured orbits is possible according to Kepler’s first law? B. A. C. Earth orbit Mars orbit D.

  21. Thought Question: Put the four orbits pictured below in order from least eccentric to most eccentric. (Enter the order of the 4 letters, then hit send.)

  22. Thought Questions: NASA wants to launch a spacecraft to go out to the planet Mars (without stopping there), and then come back. If the spacecraft follows the orbit below (dotted line), • What are the aphelion and perihelion distances? • What is the semi-major axis of the orbit? • How eccentric is the orbit? • (Enter the numerical answer for the last question on the clicker.) 1 AU 1.5 AU

  23. Comets Orbit

  24. Kepler’s Laws of Planetary Motion • Kepler’s Second Law: (SPEED DURING ORBIT) A line connecting Sun and planet sweeps out equal areas in equal times. A1 flashlet A2 CLOSER TO SUN → GREATER SPEED applet

  25. Kepler’s Laws of Planetary Motion • Kepler’s Second Law: (SPEED DURING ORBIT) In a short time t, the planet sweeps out a triangle: d: distance from Sun θ: angle between direction of motion and direction of arrow pointing from Sun to planet A2 from Sun If Kepler’s 2nd Law is true, for triangles made with the same t, the product

  26. Thought Questions: NASA wants to launch a spacecraft to go out to the planet Mars (without stopping there), and then come back. If the spacecraft follows the orbit below (dotted line), • What is θ at aphelion and perihelion? • What is the ratio of perihelion speed to aphelion speed? • (Enter the numerical answer on your clicker.) 1 AU 1.5 AU

  27. Kepler’s Laws of Planetary Motion • Kepler’s Second Law: Compare aphelion and perihelion: A2 If Kepler’s 2nd Law is true, the triangle areas are equal, so

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